Lab – Page 6 – ITP Physical Computing

Lab: DC Motor Control Using an H-Bridge

In this tutorial, you’ll learn how to control a DC motor’s direction using a DC Motor Driver.

Introduction

In this tutorial, you’ll learn how to control a DC motor’s direction using a DC Motor Driver.

To reverse a DC motor, you need to be able to reverse the direction of the current in the motor. The classic way to do this is using an H-bridge circuit. Though most motor driver chips these days are not in fact H-bridge circuits, the term still persists. This tutorial uses a Toshiba motor driver, the TB6612FNG, which can actually drive two DC motors. Both Sparkfun, Adafruit, and Pololu make breakout boards for the motor driver, though the Sparkfun one is shown in the examples below.

At the end of the lab, an alternative motor driver, the L9110H, is shown. This motor driver can only drive one motor at a time, unlike the TB6612FNG, but it’s more inexpensive than the TB6612FNG.

If you simply want to turn a motor on and off, and don’t need to reverse it, for example if you’re controlling a fan, try the tutorial on controlling high current loads with transistors.

What You’ll Need to Know

To get the most out of this lab, you should be familiar with the following concepts. You can check how to do so in the links below:

Things You’ll Need

Photo of an Arduino Nano 33 IoT module. The USB connector is at the top of the image, and the physical pins are numbered in a U-shape from top left to bottom left, then from bottom right to top right. — Arduino Nano 33 IoT

Photo of flexible jumper wires. These wires are quick for breadboard prototyping, but can get messy when you have lots of them on a board. — Arduino Nano 33 IoT

Prepare the breadboard

Connect power and ground on the breadboard to power and ground from the microcontroller. On the Arduino module, use the 5V or 3.3V (depending on your model) and any of the ground connections, as shown in Figures 10 and 11.

Figure 10 shows an Arduino Uno on the left connected to a solderless breadboard, right. The Uno’s 5V output hole is connected to the red column of holes on the far left side of the breadboard. The Uno’s ground hole is connected to the blue column on the left of the board. The red and blue columns on the left of the breadboard are connected to the red and blue columns on the right side of the breadboard with red and black wires, respectively. These columns on the side of a breadboard are commonly called the buses. The red line is the voltage bus, and the black or blue line is the ground bus.

Arduino Nano on a breadboard. — Figure 11. Breadboard view of an Arduino Nano mounted on a solderless breadboard.

As shown in Figure 11, the Nano is mounted at the top of the breadboard, straddling the center divide, with its USB connector facing up. The top pins of the Nano are in row 1 of the breadboard.

The Nano, like all Dual-Inline Package (DIP) modules, has its physical pins numbered in a U shape, from top left to bottom left, to bottom right to top right. The Nano’s 3.3V pin (physical pin 2) is connected to the left side red column of the breadboard. The Nano’s GND pin (physical pin 14) is connected to the left side black column. These columns on the side of a breadboard are commonly called the buses. The red line is the voltage bus, and the black or blue line is the ground bus. The blue columns (ground buses) are connected together at the bottom of the breadboard with a black wire. The red columns (voltage buses) are connected together at the bottom of the breadboard with a red wire.

Images made with Fritzing

Add a Digital Input (pushbutton or switch)

Connect a pushbutton to digital input 2 on the Arduino. Figure 12 shows the schematic, Figure 13 shows the breadboard view for the Uno, and Figure 14 the breadboard view for the Nano.

Schematic Diagram of a pushbutton attached to an Arduino as a digital input. The pushbutton is connected to pin 2, and to Vcc. A 10-kilohm resistor connects from the pushbutton to ground. — Figure 12. Schematic Diagram of a pushbutton attached to an Arduino as a digital input. A 10-kilohm resistor connects from the pushbutton to ground.

Breadboard Diagram of a pushbutton attached to an Arduino Uno as a digital input. The pushbutton is connected to pin 2, and to Vcc. A 10-kilohm resistor connects from the pushbutton to ground. — Figure 13. Breadboard view of a pushbutton attached to an Arduino Uno. The Arduino is connected to a breadboard as described in the image above. A pushbutton is mounted in across the center section of the breadboard. A red wire connects from the left side voltage bus to the lower right pin of the pushbutton. A blue wire connects the upper left pin of the pushbutton to digital pin 2 on the Arduino. A 10-kilohm resistor connects the upper right pin of the pushbutton to the ground bus on the left side of the board.

Breadboard Diagram of a pushbutton attached to an Arduino Nano as a digital input. The Nano is mounted across the center of the breadboadd with the USB connector facing upward. The pushbutton also mounted is connected to pin 2, and to Vcc. A 10-kilohm resistor connects from the pushbutton to ground. — Figure 14. Breadboard view of a pushbutton attached to an Arduino Nano 33 IoT.

As shown in Figure 14, the Nano is mounted across the center divide of the breadboard with the USB connector pointing up. A pushbutton is mounted in across the center section of the breadboard. A red wire connects from the left side voltage bus to the lower right pin of the pushbutton. A blue wire connects the upper left pin of the pushbutton to digital pin 2 on the Arduino. A 10-kilohm resistor connects the upper right pin of the pushbutton to the ground bus on the left side of the board.

Find a motor

Find yourself a DC motor that runs on low DC voltage within the range of 3 – 15V. This one works well for this, or this one or this one. Discarded toys and printers can be good sources of these also. The ITP free store is almost always a goldmine for discarded motors and fans. Asking classmates and second years is another good approach.

Solder leads to the motor’s terminals. The motor’s direction depends on the polarity, so it’s helpful to use different colors so you know which way the motor will turn when you hook it up.

Optional: Consider testing your motor with a bench power supply from the equipment room. Ask a teacher or resident if you need help setting one up. Begin by adjusting the voltage on the bench power supply and observe its effects. Take note of its speed at different voltages without dipping to low or too high.

Safety Warning: Running a motor at a voltage much lower or much higher than what it’s rated for could potentially damage or permanently destroy your motor. When the motor doesn’t spin, the voltage is too low. When the motor runs hot, or sounds like it’s straining, the voltage is too high.

Powering Your Motor

If your motor can run on 5V (if you’re using an Uno) or 3.3V (if using a Nano 33 IoT ) and less than 500mA, you can use the Arduino’s USB voltage. Most motors require a higher voltage and higher current draw than this, however, so you will need an external power supply. You can use any DC power supply or battery up to 15V with this motor driver as long as your motor can run at that voltage, and as long as the supply can supply as much current as your motor needs. However you choose to power this circuit, make sure the power source is compatible with your motor. For example, don’t use a 9V battery for a 3V motor.

The diagrams below show how to power the motor from an external power supply. To power directly from the Arduino’s V_cc, connect the V_MOT pin of the motor driver to the V_cc pin on the Arduino (5V on Uno, 3.3V on Nano)

Set up the Motor Driver

This tutorial uses a Toshiba motor driver, the TB6612FNG, which can actually drive two motors.There’s a Sparkfun breakout board, an Adafruit breakout board, and a Pololu breakout board for this part as well.

How The Motor Driver Works

The TB6612FNG can handle a motor supply voltage up to 15V, and it operates on a logic voltage of 2.7–5.5V. It can control an output current of 1.2A. It has two motor driver circuits, each with two logic inputs and two motor outputs. Each motor driver has a PWM input, because they are expected to be used for speed control for the motor by pulse width modulating this pin. There’s also a Standby pin that you have to connect to voltage through a 10-kilohm pullup resistor to activate the motor driver circuits.

The motor driver has the following pins. The pin numbers shown here are for the Sparkfun breakout board. The order of the pins will be different for the Adafruit and Pololu boards. The Pins are numbered here in a DIP fashion, in a U-shape from top left to bottom left, then bottom right to top right.

V_MOT – motor voltage supply input, up to 15V.
V_cc – logic voltage supply input, 2.7-5.5V
Gnd – ground
AO1 – A channel output 1. This is the first motor terminal for the first motor driver
AO2 – A channel output 2. This is the second motor terminal for the first motor driver
BO2 – B channel output 2. This is the second motor terminal for the second motor driver
BO1 – B channel output 1. This is the first motor terminal for the second motor driver
Gnd – ground
Gnd – ground
PWMB – B Channel PWM Enable. This pin controls the speed for channel B, regardless of the channel’s direction
BI2 – B channel input 2. This controls B channel output 2. To control that pin, take this pin HIGH or LOW.
BI1 – B channel input 1. This controls B channel output 1. To control that pin, take this pin HIGH or LOW.
Stdby – enables both drivers when you take it HIGH and disables them when you take it LOW
AI1 – A channel input 1. This controls A channel output 1. To control that pin, take this pin HIGH or LOW.
AI2 – A channel input 2. This controls A channel output 2. To control that pin, take this pin HIGH or LOW.
PWMA – A Channel PWM Enable. This pin controls the speed for channel A, regardless of the channel’s direction

Figure 15 shows the Sparkfun board, and Figures 16 and 17 show the Pololu board front and back. The Pololu board is labeled on the back. You can see that both boards have the same pins, even though the layouts are different.

Photo of a Motor Driver (H-bridge), model TB6612FNG — Figure 15. Motor Driver (H-bridge), model TB6612FNG

Photo of a motor driver, Pololu's TB6612FNG Dual Motor Driver Carrier (front view of the board) — Figure 16. Pololu’s TB6612FNG Dual Motor Driver Carrier (front view of the board)

Photo of a motor driver, Pololu's TB6612FNG Dual Motor Driver Carrier (back of the board) — Figure 17. Pololu’s TB6612FNG Dual Motor Driver Carrier (back of the board)

You can change the direction and speed of the motor using the motor driver. The truth table below shows how the motor driver works.

AI1	AI2	PWMA	Effect
H	L	H	Motor turns one direction
L	H	H	Motor turns the other direction
L	L	–	Motor stop
H	H	–	Motor stop
–	–	L	Motor stop

For this lab, the PWMA pin connects to a digital pin on your Arduino so you can send it either HIGH or LOW and turn the motor ON or OFF, or pulse width modulate it to control the speed. The motor logic pins are also connected to designated digital pins on your Arduino so you can set them HIGH and LOW to turn the motor in one direction, or LOW and HIGH to turn it in the other direction. The motor supply voltage connects to the voltage source for the motor, which is usually an external power supply.

Connect the motor to the Driver

Connect the motor to the driver as shown in Figures 18 – 20. Figure 18 shows the schematic, Figure 19 shows the breadboard view for an Uno, and Figure 20 shows the breadboard view for a Nano.

Figure 18. Schematic diagram of an Arduino connected to a motor driver to control a DC motor. The Arduino and switch are connected as described in the drawing above. A motor driver has been added, and is connected as follows: PWMA is connected to the Arduino’s digital pin 5. AIN1 is connected to digital pin 4. AIN2 is connected to digital pin 3 on the Arduino. AO1 and AO2 are connected to the DC motor’s two connections. The ground pins are connected to ground. V_MOT is connected to the positive terminal of a DC power source for Arduino and the motor. The power source’s negative terminal is connected to ground. The motor driver’s V_cc pin is connected to the Arduino’s voltage output (5V or 3.3V depending on your model). The Standby pin is connected to voltage through a 10-kilohm resistor. The rest of the driver pins are unconnected.

Breadboard diagram of an Arduino Uno connected to a motor driver to control a DC motor. — Figure 19. Breadboard drawing of an Arduino connected to a motor driver to control a DC motor. The Arduino and switch are connected as described in the breadboard drawing above. A motor driver has been added, straddling the center of the breadboard. PWMA is connected to the Arduino’s digital pin 5. AIN1 is connected to digital pin 4. AIN2 is connected to digital pin 3 on the Arduino. AO1 and AO2 are connected to the DC motor’s two connections. The ground pins are connected to ground. V_MOT is connected to the V_IN terminal the Arduino, and the Arduino should be powered through its DC power jack. The power source’s negative terminal is connected to ground. The motor driver’s Vcc pin is connected to the Arduino’s voltage output (5V for the Uno). The Standby pin is connected to voltage through a 10-kilohm resistor. The rest of the driver pins are unconnected. A 100-microfarad capacitor has been added connecting the voltage and ground buses close to the motor driver, to act as a decoupling capacitor.

Figure 20. Breadboard drawing of an Arduino Nano connected to a motor driver to control a DC motor. The Arduino and switch are connected as described in the breadboard drawing above. A DC power jack has been added, connected to the Nano’s ground and V_in pin (pins 14 and 15, respectively). A motor driver has been added, straddling the center of the breadboard. PWMA is connected to the Arduino’s digital pin 5. AIN1 is connected to digital pin 4. AIN2 is connected to digital pin 3 on the Arduino. AO1 and AO2 are connected to the DC motor’s two connections. The ground pins are connected to ground. V_MOT is connected to the Nano’s V_in pin, which is connected to the positive terminal of the DC power source for the motor. The power source’s negative terminal is connected to ground. The motor driver’s Vcc pin is connected to the Arduino’s voltage output (3.3V). The Standby pin is connected to voltage through a 10-kilohm resistor. The rest of the driver pins are unconnected. A 100-microfarad capacitor has been added connecting the voltage and ground buses close to the motor driver, to act as a decoupling capacitor.

Note on decoupling capacitors

If you find that your microcontroller is resetting whenever the motor turns on, add a capacitor across power and ground close to the motor. The capacitor will smooth out the voltage dips that occur when the motor turns on. This use of a capacitor is called a decoupling capacitor. Usually a 10 – 100uF capacitor will work. The larger the cap, the more charge it can hold, but the longer it will take to release its charge.

Program the microcontroller

Program the microcontroller to run the motor through the driver. First set up constants for the switch pin, the two motor driver pins, and the PWM enable pin of the motor driver. Use pin 5, one of the pins that can produce a PWM signal using analogWrite(), for the PWM enable pin.

const int switchPin = 2;    // switch input
const int motor1Pin = 3;    // Motor driver leg 1 (pin 3, AIN1)
const int motor2Pin = 4;    // Motor driver leg 2 (pin 4, AIN2)
const int pwmPin = 5;       // Motor driver PWM pin

In the setup(), set all the pins for the motor driver as outputs, and the pin for the switch as an input. Then set the PWM enable pin high so the driver can turn the motor on.

void setup() {
    // set the switch as an input:
    pinMode(switchPin, INPUT); 
 
    // set all the other pins you're using as outputs:
    pinMode(motor1Pin, OUTPUT);
    pinMode(motor2Pin, OUTPUT);
    pinMode(pwmPin, OUTPUT);
 
    // set PWM enable pin high so that motor can turn on:
    digitalWrite(pwmPin, HIGH);
  }

In the main loop() read the switch. If it’s high, turn the motor one way by taking one motor driver pin high and the other low. If the switch is low, reverse the direction by reversing the states of the two pins.

void loop() {
    // if the switch is high, motor will turn on one direction:
    if (digitalRead(switchPin) == HIGH) {
      digitalWrite(motor1Pin, LOW);   // set leg 1 of the motor driver low
      digitalWrite(motor2Pin, HIGH);  // set leg 2 of the motor driver high
    }
    // if the switch is low, motor will turn in the other direction:
    else {
      digitalWrite(motor1Pin, HIGH);  // set leg 1 of the motor driver high
      digitalWrite(motor2Pin, LOW);   // set leg 2 of the motor driver low
    }
  }

Once you’ve seen this code working, try modifying the speed of the motor using the analogWrite() function, as explained in the Analog Lab. Use analogWrite() on the PWM enable pin of the motor, and see what happens as you change the value of the analogWrite().

An Alternative Motor Driver

If you don’t have a TB6612FNG motor driver, or if you want something simpler and less expensive, the L9110H driver will also control a DC motor’s direction and speed. It can handle and input voltage of 2.5V-12V at 800mA of current. It can drive only one motor, unlike the TB6612FNG, and it can’t control stepper motors like that driver can. But it is inexpensive.

THe L9110H comes in an 8-pin DIP package. There are two inputs, labeled the A and B channels, and they are connected to two outputs, also labeled A and B. Your motor connects to the outputs and your control pins connect to the inputs. V_cc connects to the motor supply and GND connects to ground. Its pins, numbered from top left in a U shape as usual, are as follows:

OA – output for the A channel
V_cc – motor supply voltage
V_cc – motor supply voltage
OB output for the B channel
GND – ground
IA – input for the A channel
IB – input for the B channel
GND – ground

Figure 21 shows the schematic, and Figures 22 and 23 show it connected to an Uno and a Nano 33 IoT, respectively.

Schematic view of an L9110H H-bridge motor driver and a pushbutton connected to an Arduino. — Figure 21. Schematic view of an L9110H H-bridge motor driver connected to an Arduino. A pushbutton is connected to pin 2 of the Arduino as shown in the circuits above. An external DC power supply is connected to the Arduino and the motor as shown in the circuits above as well, along with a 100-microfarad decoupling capacitor. A DC motor is connected to pins OA and OB of the H-bridge. Pins Vcc are both connected to the DC power supply and pins GND are connected to ground. Pin IA is connected to pin 5 of the Arduino, and pin IB is connected to pin 6 of the Arduino.

Breadboard view of an L9110H H-bridge motor driver and a pushbutton connected to an Arduino Uno. — Figure 22. Breadboard view of an L9110H H-bridge motor driver connected to an Arduino Uno. A pushbutton is connected to pin 2 of the Arduino as shown in the circuits above. The L9110H straddles the center divide of the breadboard with pins 1 and 8 facing the top of the diagram. The Arduino should be powered through its DC power jack. The V_in pin of the Arduino connects to the L9110H’s Vcc pins (physical pins 2 and 3). The motor is connected to the L9110H’s OA and OB pins (physical pins 1 and 4). A 100-microfarad decoupling capacitor is connected to the voltage and ground buses on the breadboard. Pins GND (physical pins 5 and 8) are connected to ground. Pin IA (physical pin 6) is connected to pin 5 of the Arduino, and pin IB (physical pin 6) is connected to pin 6 of the Arduino.

Figure 23. Breadboard drawing of an Arduino Nano connected to a L9110H H-bridge motor driver to control a DC motor. The Arduino and switch are connected as described in the breadboard drawing above. A DC power jack has been added, connected to the Nano’s ground and V_in pin (pins 14 and 15, respectively). The L9110H straddles the center divide of the breadboard with pins 1 and 8 facing the top of the diagram. The V_in pin of the Arduino connects to the L9110H’s Vcc pins (physical pins 2 and 3). The motor is connected to the L9110H’s OA and OB pins (physical pins 1 and 4). A 100-microfarad decoupling capacitor is connected to the voltage and ground buses on the breadboard. THe L9110H’s ins GND (physical pins 5 and 8) are connected to ground. Pin IA (physical pin 6) is connected to pin 5 of the Nano, and pin IB (physical pin 6) is connected to pin 6 of the Nano.

To control the motor, you take one input high and the other low, just like with the previous motor driver. Since this driver has no PWM pin, you have to pulsewidth modulate the high input to manage speed control, though.

The program below controls the L9110H, setting the speed to about half the maximum whenever you push the button. To make a variable speed you could add a potentiometer and change the value of the speed variable using the potentiometer.

const int switchPin = 2;  // pushbutton input
const int motor1Pin = 5;  // H-bridge leg 1 (pin 6, 1A)
const int motor2Pin = 6;  // H-bridge leg 2 (pin 7, 2A)
 
// speed of the motor (0-255):
int speed = 127;
 
void setup() {
  // set the pushbutton as an input:
  pinMode(switchPin, INPUT);
 
  // set all the other pins you're using as outputs:
  pinMode(motor1Pin, OUTPUT);
  pinMode(motor2Pin, OUTPUT);
}
 
void loop() {
  // if the pushbutton is high, motor will turn on one direction:
  if (digitalRead(switchPin) == HIGH) {
    // set leg 1 of the H-bridge low:
    digitalWrite(motor1Pin, LOW);
    // set leg 2 of the H-bridge high:
    analogWrite(motor2Pin, speed);
  }
  // if the pushbutton is low, motor will turn in the other direction:
  else {
    // set leg 1 of the H-bridge high:
    digitalWrite(motor1Pin, speed);
    // set leg 2 of the H-bridge low:
    digitalWrite(motor2Pin, LOW);
  }
}

Get creative

Motors can be used to make things move, vibrate, rise, fall, roll, creep, or whatever you can think of, in response to user input from a digital input device (switch, floor sensor, tripwire, etc). Look inside moving toys, you’ll find a number of excellent motors and gears you can re-purpose. See the innards of a cymbal monkey below as an example. Perhaps you can re-design the user interface to a toy, using the microcontroller to mediate between new sensors on the toy and the motors of the toy.

If you used a motor in this lab, consider any toys you have that have a motor you could take control over. Charley Chimp™ has a motor that’s easy to control from an Arduino, for example.

Photo of a toy monkey. The back has been removed to reveal the inner gear mechanism that plays the cymbals. At the center of a mechanism is a DC motor. Wires have been attached to it to run the motor from an H-bridge. — Figure 21. The guts of a Charley Chimp™ cymbal-playing monkey.

You could also consider simple movements in the work of artists like Jennifer Townley, Johannes Langenkamp (instagram), Nick Yulman, or Lu Lyu.

Lab: Using a Transistor to Control High Current Loads with an Arduino

In this tutorial, you’ll learn how to control a high-current DC load such as a DC motor or an incandescent light from a microcontroller.

Introduction

In this tutorial, you’ll learn how to control a high-current DC load such as a DC motor or an incandescent light from a microcontroller. Microcontrollers can only output a very small amount of current from their output pins. These pins are meant to send control signals, not to act as power supplies. The most common way to control another direct current device from a microcontroller is to use a transistor. Transistors allow you to control the flow of a high-current circuit from a low-current source.

Video: Transistor Schematics
Video: Meet the motors
Video: Pulse-width modulating a transistor to to control a fan motor
Video: NPN Transistors
Video: Darlingtons and MOSFETs

What You’ll Need to Know

To get the most out of this Lab you should be familiar with the following concepts beforehand. If you’re not, review the links below:

What is a microcontroller
Beginning programming terms
What is a solderless breadboard and how to use one
Digital Input and output
Analog Output
Basic Electronics
Safety Warning: This tutorial shows you how to control high-current loads. This comes with a higher danger of injury from electricity than the earlier tutorials. Please be careful and double-check your wiring before plugging anything in, and never change your wiring while your circuit is powered.

Things You’ll Need

Photo of flexible jumper wires — Arduino Nano 33 IoT

Prepare the breadboard

Figure 11 shows an Arduino Uno on the left connected to a solderless breadboard, right. The Uno’s 5V output hole is connected to the red column of holes on the far left side of the breadboard. The Uno’s ground hole is connected to the blue column on the left of the board. The red and blue columns on the left of the breadboard are connected to the red and blue columns on the right side of the breadboard with red and black wires, respectively. These columns on the side of a breadboard are commonly called the buses. The red line is the voltage bus, and the black or blue line is the ground bus.

As shown in Figure 12, the Nano is mounted at the top of the breadboard, straddling the center divide, with its USB connector facing up. The top pins of the Nano are in row 1 of the breadboard.

Images made with Fritzing

Add a potentiometer

Connect a potentiometer to analog in pin 0 of the module as shown in Figure 13 through Figure 15:

Schematic view of a potentiometer. First leg of the potentiometer is connected to +5 volts. The second leg connected to analog in 0 of the Arduino. The third leg is connected to ground. — Figure 13. Schematic view of a potentiometer connected to analog in 0 of the Arduino

Breadboard view of a potentiometer. First leg of the potentiometer is connected to +5 volts. The second leg connected to analog in 0 of the Arduino. The third leg is connected to ground. — Figure 14. Breadboard view of a potentiometer connected to analog in 0 of an Arduino Uno. The potentiometer is mounted in three rows of the left center section of the breadboard. The two outside pins of the potentiometer are connected to the voltage and ground bus rows, respectively. The center pin is connected to analog in 0 of the Uno.

Figure 15. Breadboard view of a potentiometer connected to analog in 0 of an Arduino Nano. The potentiometer is mounted in three rows of the left center section of the breadboard below the Nano. The two outside pins of the potentiometer are connected to the voltage and ground bus rows, respectively. The center pin is connected to analog in 0 (physical pin 4) of the Nano.

Connect a Transistor to the Microcontroller

The transistor allows you to control a circuit that’s carrying higher current and voltage from the microcontroller. It acts as an electronic switch. You can use a bipolar Darlington transistor like the TIP120, or you can use a MOSFET like the IRF520 or FQP30N06L for this lab. All three will work the same way and use the same circuit. See Figures 16 through Figure 19 for the drawings and schematic symbols of the transistors.

Pinout drawing of a TIP-120 transistor. It is facing forward with the heat sink tab at the top and the bulging side of the component facing you. From left to right the legs are labelled 1. base, 2. collector, 3. emitter. — Figure 16. Pinout drawing of a TIP-120 transistor. From left to right the legs are labelled 1. base, 2. collector, 3. emitter.

The schematic symbol of an NPN transistor where B is the base, C is the collector, and E is the emitter. — Figure 17. The schematic symbol of an NPN transistor. B is the base, C is the collector, and E is the emitter.

NPN Transistor and N-Channel MOSFET side by side. The physical packages of the transistor and MOSFET are nearly identical. The pin out of the N-channel MOSFET is comparable to the transistor, where G of the MOSFET is the gate (equivalent of base of the transistor), D is the drain (equivalent of the collector) and S is the source (equivalent of the emitter). — Figure 18. NPN Transistor and N-Channel MOSFET side by side with a schematic diagram of the MOSFET. G is the gate (equivalent of base), D is the drain (collector) and S is the source (emitter).

Another version of the schematic symbol of an N-channel MOSFET, where G is the gate (equivalent of base), D is the drain (collector) and S is the source (emitter). — Figure 19. Schematic symbol of an N-channel MOSFET, where G is the gate (equivalent of base), D is the drain (collector) and S is the source (emitter).

The IRF520 MOSFET has the same pin configuration as the TIP120, and performs similarly with a 5V gate voltage. The FQP30N06L MOSFET has the same pin configuration, and operates on as low as 1.0V, and works well for 3.3V applications. MOSFETs can generally handle more amperage and voltage, and switch a little faster (the difference is in microseconds, so you won’t notice), but they are more sensitive to static electricity damage. They are grouped into N-Channel and P-Channel, which are equivalent to NPN and PNP bipolar transistors.

All three transistors mentioned here are designed for switching high-current loads. All of them have built-in protection diodes. Each has three connections Table 1 below details their connections.

Bipolar Transistor	MOSFET	Connection
Base	Gate	Connects to microcontroller output
Collector	Drain	Connects to power through load
Emitter	Source	Connects to ground

Table 1. Names of the pins on the bipolar transistor and the equivalent names on the MOSFETs

The datasheets for each of the recommended transistors can be found below:

TIP120 Bipolar Darlington Transistor
IRF520 MOSFET – good for 5V control
FQP30N06L MOSFET – good for 3.3V control

Here’s the main operating principle of using a transistor as a switch: When a small voltage and current is applied between the base (or gate) and the emitter (or source), the transistor allows a larger current to flow between the collector (or drain) and emitter (or source).

Figures 20 through 22 show how to connect the transistor.

Figure 20. Schematic view of a potentiometer and transistor connected to an Arduino. First leg of the potentiometer is connected to +5 volts. The second leg connected to analog in 0 of the Arduino. The third leg is connected to ground. The base (or gate) of the transistor is connected to digital pin 9 of the Arduino through a 1-kilohm resistor. The emitter (or source) is connected to ground.

Figure 21. Breadboard view of a potentiometer and transistor connected to an Arduino. First leg of the potentiometer is connected to +5 volts. The second leg connected to analog in 0 of the Arduino. The third leg is connected to ground. The base (or gate) of the transistor is connected to digital pin 9 of the Arduino through a 1-kilohm resistor. The emitter (or drain) is connected to ground.

Figure 22. Breadboard view of a potentiometer and transistor connected to an Arduino Nano. First leg of the potentiometer is connected to +3.3 volts. The second leg connected to analog in 0 of the Arduino. The third leg is connected to ground. The base (or gate) of the transistor is connected to digital pin 9 of the Arduino through a 1-kilohm resistor. The emitter (or drain) is connected to ground.

Connect a Motor and Power Supply

Attach a DC motor to the collector (or drain) of the transistor as shown in Figures 23 through 25. Most motors will require more current than the microcontroller can supply, so you will need to add a separate power supply as well. If your motor runs on around 9V, you could use a 9V battery. A 5V motor might run on 4 AA batteries (6V). You could also use a 12-volt DC wall adapter and a 5-volt regulator. A 12V battery may need a 12V DC wall adapter, or a 12V battery. The ground of the motor power supply should connect to the ground of the microcontroller on the breadboard.

Add a 1N400x power diode in parallel with the collector and emitter of the transistor, pointing away from ground. The diode protects the transistor from back voltage generated when the motor shuts off, or if the motor is turned in the reverse direction. Used this way, the diode is called a protection diode or a snubber diode. You can omit the diode if you don’t have one, as the transistors recommended here all have a built-in protection diode

Figure 23. Schematic view of a potentiometer connected to analog in 0 of the Arduino. A transistor is connected to Digital Pin 9. A DC motor connects to the transistor and a DC jack. The DC jack connects its positive wire to the first wire of the DC motor. The negative wire of the DC jack connects to ground. The second wire of the DC motor connects to the collector (or drain) of the transistor. A 1N400x diode’s anode is connected to the collector (or drain), and its anode is connected to ground.

Figure 24. Breadboard view of an Arduino connected to a potentiometer, a transistor, a DC motor, and a DC jack. A transistor is connected to Digital Pin 9. A DC motor connects to the transistor and a DC jack. The DC jack connects its positive wire to the first wire of the DC motor. The negative wire of the DC jack connects to ground. The second wire of the DC motor connects to the collector (or drain) of the transistor. A 1N400x diode’s anode is connected to the collector (or drain), and its anode is connected to ground.

Figure 25. Breadboard view of an Arduino Nano connected to a potentiometer, a transistor, a DC motor, and a DC jack. A transistor is connected to Digital Pin 9 through a 1-kilohm resistor. A DC motor connects to the transistor and a DC jack. The DC jack connects its positive wire to the first wire of the DC motor. The negative wire of the DC jack connects to ground. The second wire of the DC motor connects to the collector (or drain) of the transistor. A 1N400x diode’s anode is connected to the collector (or drain), and its anode is connected to ground.

Be sure to add the diode to your circuit correctly. The silver band on the diode denotes the cathode which is the tip of the arrow in the schematic, like so in Figure 26:

Schematic representation and physical representation of a diode. The schematic form shows an equilateral triangle with a line bisecting the triangle equally from one point to and through the middle of the opposing flat side. There is also a line perpendicular to the other line that also intersects the triangle at its bisected point. The cathode is represented by the side of the schematic with the line. The drawing of the physical form of the diode looks like a black resistor with only a single grey stripe on one side. The side with the stripe represents the cathode — Figure 26. Schematic representation and physical representation of a diode. The silver band on the diode indicates the anode end.

Connect a Lamp Instead of a Motor

You could also attach a lamp using a transistor. There are many 12V incandescent lamps, designed for use in track lighting, gallery lighting, and so forth. Nowadays, there are many 12V DC LED equivalents of the 12V AC lamps as well. Here are a few examples:

Bi-Pin Socket for GU5.3/G4/GX5.3/GY6.35/GZ4 Base Bulbs – This socket works with the lamps below, and many others.
GY6.35 LED Landscape Light Bulb – 40 Watt Equivalent – Bi-Pin LED Bulb – 450 Lumens
GY6.35 LED Landscape Light Bulb – 40 Watt Equivalent – Bi-Pin LED Bulb – 275 Lumens
MR16 LED Single Color Landscape Light Bulb – 30 Degree – 35W Equivalent
12V LED strip light, 19 in.

The lamp circuit in Figures 27 through 29 assumes a 12V lamp. MOSFETs are generally best for switching incandescent and LED lamps, so the circuit below uses a MOSFET. In the lamp circuit, the protection diode is not needed, since there’s no way for the polarity to get reversed in this circuit.

Figure 27. Schematic view of a potentiometer, MOSFET, and lamp connected to an Arduino. The gate of a MOSFET transistor is connected to Digital Pin 9 of the Arduino. A 12V lamp connects to the drain of the transistor and a DC jack. The DC jack connects its positive wire to the first wire of the lamp. The negative wire of the DC jack connects to ground. The second wire of the lamp connects to the drain of the transistor. The source of the transistor connects to ground.

Figure 28. Breadboard view of a potentiometer, MOSFET, and lamp connected to an Arduino. The gate of a MOSFET transistor is connected to Digital Pin 9 of the Arduino. A 12V lamp connects to the drain of the transistor and a DC jack. The DC jack connects its positive wire to the first wire of the lamp. The negative wire of the DC jack connects to ground. The second wire of the lamp connects to the drain of the transistor. The source of the transistor connects to ground.

Figure 29. Breadboard view of a potentiometer, MOSFET, and lamp connected to an Nano. The gate of a MOSFET transistor is connected to Digital Pin 9 of the Nano. A 12V lamp connects to the drain of the transistor and a DC jack. The DC jack connects its positive wire to the first wire of the lamp. The negative wire of the DC jack connects to ground. The second wire of the lamp connects to the drain of the transistor. The source of the transistor connects to ground.

Program the microcontroller

Write a program to test the circuit, whether it’s a motor or a lamp. Your program should make the transistor pin an output in the setup method. Then in the loop, it should turn the motor on and off every second, just like the blink sketch does.

const int transistorPin = 9;    // connected to the base of the transistor
 
 void setup() {
   // set  the transistor pin as output:
   pinMode(transistorPin, OUTPUT);
 }
 
 void loop() {
   digitalWrite(transistorPin, HIGH);
   delay(1000);
   digitalWrite(transistorPin, LOW);
   delay(1000);
 }

Now that you see it working, try changing the speed of the motor or the intensity of the lamp using the potentiometer.

To do that, read the voltage of the potentiometer using analogRead(). Then map the result to a range from 0 to 255 and save it in a new variable. Use that variable to set the speed of the motor or the brightness of the lamp using analogWrite().

const int transistorPin = 9;    // connected to the base of the transistor
 
 void setup() {
   // set  the transistor pin as output:
   pinMode(transistorPin, OUTPUT);
 }
 
 void loop() {
   // read the potentiometer:
   int sensorValue = analogRead(A0);
   // map the sensor value to a range from 0 - 255:
   int outputValue = map(sensorValue, 0, 1023, 0, 255);
   // use that to control the transistor:
   analogWrite(transistorPin, outputValue);
 }

For the motor users: A motor controlled like this can only be turned in one direction. To be able to reverse the direction of the motor, an H-bridge circuit is required. For more on controlling DC motors with H-bridges, see the DC Motor Control lab.

Come Up with an Application

Now that you’ve got motor or lamp control, come up with an application.

If you used a motor in this lab, consider any toys you have that have a motor you could take control over. Charley Chimp™ has a motor that’s easy to control from an Arduino, for example.

You could also consider simple movements in the work of artists like Jennifer Townley, Johannes Langenkamp (instagram), Nick Yulman, or Lu Lyu.

You’ve got the beginnings of a good desk lamp or table lamp, if you chose to use a light bulb in this lab. How will you control it? How will you mount the switchor the dimmer knob? You might also want to consider a gooseneck pipe to mount your socket on, and a socket that goes with it. Here are a few inspirations:

Heng Balance Lamp
LZF Swirl
Rux Designs Stickbulb
Lyn Godley’s Crinkle Lamp and wineglass chandeliers
Julio Leparc

Lab: Soldering

In this tutorial you’ll learn the basics of soldering for electronics.

Introduction

If you’re going to do any electronics work, you’re going to have to do some soldering, or have someone help you do it. Many people fear it before they’ve done it, but it’s really pretty simple to do. This exercise will show you how to solder a DC Power connector to a set of wires for a breadboard.

In order to get the most out of this tutorial, you should have a basic understanding of electrical circuits, so you understand why you’re soldering, and you should know what a solderless breadboard is.

You might also find this video on soldering by Andy Sigler and this video on desoldering helpful.

Soldering is a process in which you use a metal alloy with a low melting point to fuse together two other pieces of metal. It’s used in electronics all the time, because it ensures a mechanically solid connection between two materials that’s also electrically conductive. To do this, you heat the alloy, called solder, until it melts, and let it run across the two metal pieces you’re attempting to join.

There are many different ways to solder, but the most common for hobbyists uses a handheld soldering iron and a reel of solder wire. That’s the process that’s demonstrated here.

Things You’ll Need

Photo of a solderable DC power jack. It is shown disassembled, with the metal insides separate from the plastic insulator sleeve — Figure 1. Solderable DV power Jack. You can find this particular model on Jameco.com

Photo of breakaway header pins. There are 20 pins in one row. The pins are all 0.5 inch (1.3cm) long, and separated by 0.1 inch (2.5mm) plastic spacers. The plastic is scored so that the pins can be broken off one at a time. — Figure 2. Breakaway header pins

Photo of helping hands tool. The tool has a metal base witha swivel joint at the top. The swivel joint holds a metal bar approximately 6 inches (15cm) long. Each end of the bar has another swivel joint with a metal clip mounted on it. — Figure 3. Helping hands tool

Photo of a soldering iron. The base of the iron is approximately 5 inches (13cm) on a side. The left side is reaised and has a power switch and a temperature knob on the front. The right side has a metal coil, and the iron itself is inserted in the coil. The iron is approximately 8 inches (20cm) long, metal with a plastic handle. The handle has a thick wire coming out of the back that attaches to the base below the temperature knob. — Figure 4. Soldering iron

Photo of a roll of solder wire. The wire is thin, approximately 0.05 inches (1mm) in diameter. It is quite soft, and breaks easily. — Figure 5. A roll of solder wire

Photo of two pieces of 22AWG hookup wire. The wire is approximately 0.05 inches (1mm) in diameter, and clad in a plastic insulation. These two wires have red and black insulation, respectively. — Figure 6. 22AWG hookup wire

Photo of a hot glue gun. — Figure 7. Hot glue gun

Wire strippers. The jaws of this wire stripper have multiple hole sizes so that it can strip wires of variable sizes. — Figure 8. Wire stripper tool

In the steps that follow, you’ll connect jumper wires to a power connector. When you’re prototyping a circuit, you need all of your parts to have connections that can fit firmly in a solderless breadboard. Many electronic components and connectors don’t have such connections, so you need to solder them on. The DC power jack shown in this exercise is one such connector. It comes with no wires, just connections onto which you’re expected to solder your own wires. You’ll solder wires onto it, and then you’ll solder a pair of stiff header pins onto the ends of the wires.

Preparing the parts

Cut a red and a black wire about four inches (10cm) in length. Strip the ends back about 1/4 of an inch (1/2 cm). Bend a hook on one end of each wire. Unscrew the power jack. As shown in Figure 9, connect the red wire to the hole in the the center tab of the power, and the black to the hole in the outside tab. Use pliers to crimp the hooked wires to their connections on the jack. If the connections aren’t soldered, you’ll get an inconsistent connection at best, and a short circuit at worst.

Photo of a DC power jack with 22AWG wires hooked into its two solder tabs. The wires are not yet soldered. — Figure 9. A DC power jack ready to solder

Heating the Soldering Iron (and the connections)

Heat up your soldering iron. It doesn’t need to be cranked to its maximum heat. For most small jobs like this, 600-700 degrees Fahrenheit (315-370 C) will work just fine. You really only need the iron hot enough to heat the metal connections so that they’ll melt the solder.

The best solder joints are those where the two metal connections to be joined are heated up together, and the solder is then melted by the heat of the connections. That way, all three metals cool down together. As they cool, they contract. You want them to contract together, so there is no cracking of the joint between them.

Make sure the two pieces of metal are touching each other firmly. Use a helping hand or a clamp to hold them in place. When they’re solidly touching, and held firmly by your clamp or helping hands, touch the iron to the joint between the wire and the metal to heat the joint (see Figure 10). Then touch the solder to the joint (NOT to the iron) until it melts. This should make a clean solder with a small blob of solder.

You may find that it takes longer to heat the connection in order for the solder to melt. The larger a connector is, the more time it takes to heat. This is because the metal of the connector is conducting the heat away from the joint. If your connector is too big, you may need to use a mechanical joint, as opposed to a solder joint. The DC power jacks shown in this tutorial will solder just fine, however.

As the solder cools down, its surface will go from shiny to a more matte surface. When it cools down, test the joint by wiggling it to make sure it’s firm.

Repeat the process with the other wire and the other part of the connector.

Photo of a wire hooked into the metal tab of a power connector. Both are held by a pair of helping hands clips. A soldering iron is touched to the joint between the wire and the tab. A piece of solder is touched to the joint, but is not touching the iron directly. — Figure 10. Preparing the solder joint. The solder should be touched to the joint, not to the iron.

Twist the wires together and thread them through the sleeve of the jack.

The result should look like this in Figure 11:

Photo of a soldered power connector. The wires are soldered to the two tabs of the connector, then twisted together before they are threaded into the plastic insulating sleeve of the connector. — Figure 11. The inside of a soldered power connector, with red and black wires twisted together.

Soldering the Header Pins

The two wires are now properly separated inside the connector, but the other ends can move freely. Even though these two ends can fit firmly in a breadboard, it can be dangerous to leave them loose. They might touch each other while you have the connector plugged in, causing a short circuit.

Header pins(Figure 12) are a great way to maintain the spacing between wires that you need to fit into a breadboard. If you solder two of them to the ends of your wires, with the metal spacer still on them, they’ll keep your wire leads safely apart.

Trim the ends of the wires to the same length, and strip them back to about 1/8th of an inch. Break off two header pins and hold them in one clip of a helping hands device. Clip the wires in the other clip, and align them with the header pins like so in Figure 13:

Photo of two header pins held in a helping hands tool. The headers are touching two wires, one red, one black. The wires and the header pins are not soldered together. — Figure 13. Header pins ready to be soldered to the ends of your wires.

Solder the wires to the headers. Move quickly, as the plastic spacer between the headers can melt (that’s another reason not to heat your iron too hot). When you’re done soldering, you should have two separate blobs like this in Figure 14:

Photo of two header pins held in a helping hands tool. The headers are touching two wires, one red, one black. The wires and the header pins are soldered together. — Figure 14. Header pins successfully soldered to wires.

If you can’t see space between the two solder joints, de-solder them and do it again. You need to be sure there’s no connection between these wires that can cause a short circuit, and the best way to do that is to leave space.

Take a hot glue gun and surround the bare connections to insulate them and provide some strain relief. When you’re done, you should have a connection like this in Figure 15:

Photo of an assembled DC power connector. Red and black wires, twisted together, protrude from the connector. They terminate in a pair of header pins, The connection between the wires and the header pins, previously soldered, is hot glued for insulation. — Figure 15. DC power connector assembled, with the wire-to-header connections insulated with hot glue.

Make sure you can tell which pin is connected to the red wire and which is connected to the black.

Testing

Before you connect it to power, take a meter and check the connections for continuity. The center pin should be connected to the red wire, and the outer rim should be connected to black. When that’s good, you’re ready to use it.

What Else Can I Solder?

Any time you have loose mechanical connections, you should solder them if you can. For example, many common potentiometers have ring contacts(Figure 16). If you loop the wires around the rings as shown in Figure 17, you get inconsistent readings from your potentiometer. Solder the leads if they are loose.

Photo of a potentiometer with metal ring contacts. — Figure 16. A potentiometer with ring contacts, ready for soldering.

Photo of a potentiometer with ring contacts. Three wires are soldered to the three contacts, from left to right: black wire, blue wire, red wire. — Figure 17. Potentiometer with wires successfully soldered.

Many breadboard-friendly printed circuit boards come without headers soldered on. One of the most common mistakes beginners make with these boards is to push them into a breadboard using headers, but with no solder. This will also give inconsistent readings. Figure 18 shows an ADXL335 accelerometer module pins are properly soldered.

Figure 18. An ADXL335 accelerometer module. There are six pins along the bottom, labeled GND, Z, Y, X, 3V, and ST (left to right). These pins are properly soldered (You can find this accelerometer on adafruit.com)

When in doubt, if you have loose connections, solder them!

For more on soldering, check out Adafruit’s soldering tutorial.

Digital Input & Output

Introduction

This is an introduction to basic digital input and output on a microcontroller. In order to get the most out of it, you should know something about the following concepts. You can check how to do so in the links below:

These videos will help in understanding digital inputs and outputs:

Digital Inputs

When you’re trying to sense activity in the physical world using a microcontroller, the simplest activities you can sense are those in which you only need to know one thing about the physical world: Whether something is true or false. Is the viewer in the room or out? Are they touching the table or not? Is the door open or closed? In these cases, you can determine what you need to know using a digital input, or switch.

Digital or binary inputs to microcontrollers have two states: off and on. If voltage is flowing, the circuit is on. If it’s not flowing, the circuit is off. To make a digital circuit, you need a circuit, and a movable conductor which can either complete the circuit, or not.

Figure 1. Schematic of a Digital Input to a microcontroller

Figure 1 shows the electrical schematic for a digital input to a microcontroller. The current has two directions it can go to ground: through the resistor or through the microcontroller. When the switch is closed, the current will follow the path of least resistance, to the microcontroller pin, and the microcontroller can then read the voltage. The microcontroller pin will then read as high voltage or HIGH. When the switch is open, the resistor connects the digital input to ground, so that it reads as zero voltage, or LOW.

On an Arduino module, you declare the pin to be an input at the top of your program. Then you read it for the values 1 (HIGH) or 0 (LOW), like so:

void setup() {
 // declare pin 2 to be an input:
 pinMode(2, INPUT);
 declare pin 3 to be an output:
 pinMode(3, OUTPUT);
}
 
void loop() {
 // read pin 2:
 if (digitalRead(2) == 1) {
   // if pin 2 is HIGH, set pin 3 HIGH:
   digitalWrite(3, HIGH);
 } else {
   // if pin 2 is LOW, set pin 3 LOW:
   digitalWrite(3, LOW);
}

Digital output

Just as digital inputs allow you to sense activities which have two states, digital or binary outputs allow you to control activities which can have two states. With a digital output you can either turn something off or on. Figure 2 is the schematic diagram for digital output controlling an LED:

Digital outputs are often used to control other electrical devices besides LEDs, through transistors or relays. For more information on that, see these notes on controlling high-current circuits.

On an Arduino module, you declare the pin an output at the top of the program just like you did with inputs. Then in the body of the program you use the digitalWrite() command with the values HIGH and LOW to set the pin high or low, as you’ve seen above.
Here’s a simple blinking LED program in Arduino:

void setup() {
  pinMode(13, OUTPUT);
}
 
void loop() {
  digitalWrite(13, HIGH);
  delay(1000);
  digitalWrite(13, LOW);
  delay(1000);
}

As inputs, the pins of a microcontroller can accept very little current. Likewise, as outputs, they produce very little current. The electrical signals that they read and write are mainly changes in voltage, not current. When you want to read an electrical change that’s high-current, you limit the current input using a resistor. Similarly, when you want to control a high-current circuit, you use a transistor or relay, both of which allow you to control a circuit with only small voltage changes and minimal current. Related video: Transistor

Lab: Components

In this lab you will learn about some of the components you’ll use frequently when making electronic circuits.

Introduction

In this lab you will learn about some of the components you’ll use frequently when making electronic circuits. For more on any given component, please check out its datasheet. There are no specific activities in this lab other than to examine the components and to familiarize yourself with them.

Video: Schematics 5

A datasheet or spec sheet is a document (printed or .pdf) that describes the technical characteristics of a sensor, electronic component, product, material or other. It includes details on how to use the component in a circuit and other useful design info on how to integrate it into a system together with specifications on performance and other characteristics that are important to know.

Components

Video: Datasheets

Voltage Regulator

5-volt regulator, model 7805. This component has three legs and a tab at the top with a hole in it. If you hold the component with the tab at the top and the bulging side of the component facing you, the legs will be arranged, from left to right, voltage input, ground, and voltage output. — Figure 1. 5-volt voltage regulator, model 7805

Different electronic circuits operate at different voltages. For example, the Arduino Uno operates at 5 volts, while the Arduino Nano 33 IoT and BLE, and the MKR series, operate at 3.3 volts. A voltage regulator takes a range of DC voltage as input and convert it to a constant voltage. For example, this regulator shown in Figure 1, a 7805 regulator, takes a range of 9 – 15 volts DC input and converts it to a constant 5-volt output. Using this regulator, you could power a 5-volt motor or a string of addressable LEDs from a 12-volt power source.

Note the label on the regulator that reads “7805”. This is the part number. Other parts have the same physical form factor, however. The form factor, called the package, is not dependent on what the actual part is. This is a TO-220 package. Many different parts use this same package, for example, and not all of them are voltage regulators. Also, sometimes the same part will come in different packages, so you can use it in different size devices.

The 7800 series regulators come in many different voltages. 7805 is a 5-volt regulator. 7809 is a 9-volt regulator. 7812 is a 12-volt regulator. All the regulators of this family have the same pin connections. In the image above, the left leg is connected to the input voltage. The middle leg is connected to ground. The right leg is the output voltage.

Link to 7805 datasheet

3.3-volt regulator, model LD111733V. This component has three legs and a tab at the top with a hole in it. If you hold the component with the tab at the top and the bulging side of the component facing you, the legs will be arranged, from left to right, ground, voltage output, and voltage input. The back tab is attached to the voltage output pin. — Figure 2. 3.3V voltage regulator

3.3V regulators are also common. Note that not all regulators which share the same package have the same pin configuration. For example, the LD1117V33, a 3.3V regulator shown in Figure 2, comes in the same physical package as a 7805, but its pins are in a different order. The LD1117V33’s pins, from left to right, are ground, output voltage, input voltage.

LED

Figure 3. LEDs. Shown here are four LEDs. The one on the right is an RGB LED. You can tell this because it has four legs, while the others have only two legs.

Solderless Breadboard

Solderless breadboards are reusable prototyping tools for electronics that allow you to build and experiment with circuits simply by plugging components in and out of its rows and columns. They come in different shape and sizes. Figure 4 shows a typical short solderless breadboard. It has two rows of holes on either side of the board, usually used as voltage and ground buses. The board is turned in this photo so that the bus rows are on top and bottom. In the center of the board, there are thirty rows of holes. There is a divider down the center of the board that breaks up the rows of holes into separate rows. There are five holes per row on the center left and on the center right of each row.

Resistors

Resistors resist the flow of electrical current. When placed in series, they reduce the voltage, and limit the current. The bands on a resistor indicate the resistor’s value. Here’s a handy resistor color code calculator. Resistors come in 4-band, 5-band, and 6-band models. In a 4-band resistor, the bands represent the first digit, second digit, multiplier, and tolerance. The resistors shown in Figure 5 are 4-band resistors marked red, red, brown, and gold, for 2, 2, times 10¹, 5%. In other words, these are 220 ohm resistors, +/-5%. The resistor color code calculator explains the bands for 5-and 6-band resistors as well.

Potentiometers

Figure 6. Potentiometer. The one shown here has three legs spaced 0.1 inches apart and can be therefore mounted on a solderless breadboard.

Force Sensing Resistors

Force sensing resistors are sensors that change their resistance in response to force. They’re usually used to make analog alternatives alternatives to buttons. They’re made of a substrate of resistive rubber between two layers of conductive ink on a plastic film. They come in a variety of form factors. Figure 8 shows a pair of force sensors about 2.5cm across, sized for finger presses. There are a few companies who make them, including Interlink, Ohmite, and Tekscan.

Flex Sensors (Flex Resistors)

Flex sensors are similar to force sensing resistors in construction, but they change their resistance as they bend. They are typically about the length of a finger, and they work well for measuring the bend of a finger. Spectrasymbol make these.

Photo of a flex sensor. A plastic strip approx. 0.25 inches wide by 6 inches long, with pins at one end. When you bend the sensor, the resistance between the pins changes — Figure 9. Flex sensor

Force Sensing Potentiometers

Force Sensing Potentiometers, sometimes called SoftPots, are also similar to force sensing resistors. The difference is that a force sensing resistor gives one value wherever you press on it, while a force sensing potentiometer acts like a normal potentiometer: the value changes depending on where along its length you press. They come in linear and round form factors. Ohmite, Interlink, and Spectrasymbol make FSPs.

Light-Dependent Resistors (Photocells)

Photocell, or light-dependent resistor. This component has a round top and two wire legs. You measure the resistance between the two legs and expose the top to a varying light source in order to vary the resistance between the two legs. — Figure 11. Photocell, or light-dependent resistor

Light-dependent resistors, or photocells, are variable resistors whose resistance changes with the intensity of the light falling on the resistor. Photocells, as seen in Figure 11, are made with cadmium sulfide, which is a toxic chemical. Increasingly, they are being replaced in hobbyist kits by phototransistors, which are somewhat less toxic (see below).

Thermistors

Thermistor, or temperature-dependent resistor. This component has a bulbous top and two wire legs. You measure the resistance between the two legs and expose the top to a varying temperature in order to vary the resistance between the two legs. — Figure 12. Themistor, or temperature-sensitive resistor

Thermistors, seen in Figure 12, are variable resistors whose resistance changes as the temperature changes. You measure the resistance between the two legs of the thermistor and expose the top to a varying temperature in order to vary the resistance between the two legs.

Switches

Pushbuttons. These ones are designed to be mounted on a solderless breadboard. They have four legs spaced 0.2 inches apart on both sides of the component. — Figure 13. Pushbuttons, also called momentary switches

Switches are one form of digital input. There are many kinds of switches. The two most useful categories are momentary switches, which remain closed only when you press them, and toggle switches, which stay in place after you switch them.

Pushbuttons are a common type of momentary switch. The pushbuttons in the photo in Figure 13 above are designed to be mounted on a circuit board. They are very small, less than 1 centimeter on a side. They have four pins. When the button is facing you, top two are connected to each other, and the bottom two are connected to each other. Pushing the button connects the top pins to the bottom pins.

Toggle switches (Figure 14) stay in one position when you flip them. Wall light switches are common examples of toggle switches. Unlike a momentary switch, a toggle switch can be used to turn a device on or off, because they stay in one state when you remove your hand. The toggle switches below each have three connectors, also called pins or legs. They’re usually labeled C for common, NO for Normally Open, and NC for Normally Closed. When you switch the switch, it will open the connection between the common pin and the normally closed pin, and close the connection between the common pin and the normally open pin. Switch it the other way, and you will reverse the connection.

Toggle switches. These switches are approximately half an inch (1cm) long, and have a switch on top that moves from one side to the other. They typically have two or three legs. — Figure 14. Toggle switches

Rotary Encoder

A rotary encoder is a sensor that usually looks a bit like a potentiometer. It has a central shaft that you can turn with your fingers, or with an axle. It produces a pair of electrical pulses as you turn the shaft of the encoder, one slightly before or after the other, depending on the direction you are turning the shaft. Unlike a potentiometer, they can turn endlessly. They are used both as tangible controls, when you want a knob that turns endlessly, and as rotary sensors for motors and axles. The encoder in Figure 15 has three pins. The center is connected to ground, and the two side pins produce the pulses. The Encoder library for Arduino is useful for reading these.

Capacitors

Diodes

Transistors

Video: Schematics 3 – Transistors

Transistors act as electronic switches. When you put a small voltage across the base and emitter, the transistor allows a larger current and voltage to flow from the collector to the emitter. The transistor shown above in Figure 21, a TIP120, is a type of transistor known as a Darlington transistor. It is usually used to control high-current loads like motors. Note that it uses the same physical form factor, or package, as the voltage regulator above (the TO-220 package).

The TIP120 shown here is jus one option for controlling high current loads. Metal Oxide Semiconductor Field Effect Transistors, or MOSFETS, are also good for controlling motors, lights, and other high current loads. These two models also come in the same physical package as the TIP120. The IRF510 and IRF520 MOSFETs have the same pin configuration as the TIP120, and perform similarly with a 5V gate voltage. The FQP30N06L MOSFET has the same pin configuration, and operates on as low as 1.0V, and works well for 3.3V applications. MOSFETs can generally handle more amperage and voltage, but are more sensitive to static electricity damage.

Phototransistors

Phototransistors are transistors, but instead of being controlled by electricity, they are controlled by light. The base of a phototransistor is photosensitive. They often look like LEDs. The ones in Figure 15, Everlight model ALS-PT243-3C/L177, have flat tops to differentiate them from LEDs. The short leg of a phototransistor is the emitter, and the long leg is the collector. The lens is the base. To use them in an analog input circuit. emitter goes to voltage and the collector goes to your input pin. A 10-kilohm pulldown resistor connects the input pin to ground, just as it would if you were using a photocell..

Power Jacks

DC Power jacks are used to connect your breadboard to a DC power supply that you can plug into a wall. They’re less common in microcontroller circuits now that USB power connectors and USB wall plugs are common, but they are still very handy when you have only a DC power supply to work with. The one in Figure 22 has screw terminals on the back to which you can connect wires to connect to your breadboard. It is a 2.1mm inside diameter, 5.5mm outside diameter jack, which is a very common size.

Battery Holders

This is a square box that can hold four AA size batteries. There are four columns in the box, each with a spring in it. The negative end of the battery (the flat end) contacts the spring. The positive end of the battery (the end with a small protrusion) connects to the end opposite the spring. The batteries sit parallel to each other, each facing the opposite direction of its neighbors. Two round metal terminals protrude from one corner of the box, one red and one black. These connect to a 9-volt battery — Figure 23. AA battery holder

9V battery snap. This flat component with rounded ends has two round metal mounts on one side. One is slightly bigger than the other, about half an inch (3-2cm) across. They are designed to snap onto a 9-volt battery. There is a pair of wires coming out one end that has a DC power plug attached to it. This can plug into a DC power jack. — Figure 24. 9V battery snap with DC power plug on it.

Battery connectors like the ones shown in Figures 23 and 24 are good for connecting batteries to your project. The one in Figure 20 can hold 4 AA batteries, and has a 9V battery snap on the outside. The one in Figure 21 has a DC power jack on one end, and a 9V battery snap on the other end.

Motors

Servo Motor

Video: Analog Output: Servo

A servo motor is a motor paired with an encoder (e.g. a potentiometer) to provide position/speed readings and control messages in a feedback loop. This loop is used to precisely control of the servo’s degree of rotation. RC servomotors like the one shown in Figure 25 can only turn 180 degrees. They are often used for the rudder control on remote control planes and cars. The plastic bits shown in the photo are called horns, and they attach to the shaft to let you attach the motor to the mechanism that you want to control.

DC Motor

DC toy motor, hobby size. This motor is a metal tube with flattened sides, approximately 2 in. (5cm) long. a thin shaft at one end spins when the motor is on. Two small metal tabs or wires protrude from the other end to connect the motor to your circuit. — Figure 26. Small DC motor, 130 size

Motor Driver

A motor driver, sometimes called an H bridge, is an electronic circuit that enables a voltage to be applied across a load in either direction. They are often used to control the direction of DC motors. The motor driver in Figure 27 is a Toshiba model TB6612FNG. It is a good option for both 5V (from an Arduino Uno) and 3.3V (from a Nano 33 IoT) control of DC motors and stepper motors.

Electromechanical Relay

These components are rectangular, approximately three quarters of an inch long and half an inch tall, with seven pins on the bottom. — Figure 28. Electromechanical relays: top and left views as well as inside.

Like transistors, relays are electronic switches. Electromechanical relays contain a small coil that, when energized, creates a magnetic field that moves a small metal armature to open or close an electrical contact. Relays can handle higher current than transistors and can be used for AC or DC loads. However, because they rely on a physical mechanism, they are slower and more prone to wearing out. If you want to control a relay with the Arduino, you will need to use a transistor as an intermediary because most relays draw more current than the Arduino’s output pins can supply.

Relays come in many packages. The ones shown in Figure 28 are for controlling relatively low power loads. For more on relays, see the Transistors, Relays, and Controlling High-Current Loads topic page.

Screw Terminal

These components have a small round depression on the top, inside of which is a screw. On the side there is a square hole into which you can insert a wire. On the bottom, there is a pin connected to the square socket. There is one screw, socket, and pin per connection. — Figure 29. Two-contact screw terminal

Screw terminals, as seen in Figure 29, are electrical connectors that hold wires in place with a clamping screw. They allow for a more secure connection than female headers and more flexibility than soldering a wire in place. There is one screw, socket, and pin per connection.

Sensor Modules

Increasingly, sensors are no longer just simple components that output a changing resistance or capacitance. Sensor modules are application-specific integrated circuits (ASICs) which read a particular physical property and give you a measurement via a synchronous serial communications channel like I2C.

Figure 30 shows four different I2C sensors: a ten-channel spectrometer, at the top, which measures the intensity of light in ten different frequencies; An accelerometer, on the right (read below for more); a time-of-flight distance ranging sensor, that measures distance using an infrared low-power laser, on the bottom; and a light sensor that functions as both a particle sensor and a pulse oximeter, on the left, by measuring the change in color of your blood through the skin of your finger.

These are only a few of the many sensor modules available that can be connected to a microcontroller via I2C. You’ll see color and gesture sensors, temperature and humidity sensors, and many more. They are often available as breadboard-friendly breakout board modules, like the ones shown here, that are typically a circuit board that’s a few centimeters square, with holes on one side spaced 0.1″ apart so you can attach pins to plug it into a breadboard.

Photo of four different I2C sensor modules — Figure 30. Various I2C sensors

Accelerometer

Accelerometers are sensors which measure a changing acceleration (Figure 31). They are typically part of sensors called Inertial Measurement Units, or IMUs. They are useful for measuring the tilt of a body, or for measuring the force of an impact. They come in both digital and analog forms. A typical accelerometer measures acceleration along three axes, all perpendicular to each other. Accelerometers are increasingly built into microcontroller modules and other electronic devices. There is accelerometer and a gyrometer built into the Nano 33 IoT.

Infrared Distance Ranger

Sharp makes a line of infrared distance ranging sensors that measure distance in about a 1-meter range using infrared light. The one shown in Figure 32 has an analog voltage output.

Photo of an infrared distance sensor. It has two lenses on top, one for the light and one for the sensor, and three pins on the side, to plug into a solderless breadboard. — Figure 32. IR distance ranger

Ultrasonic Distance Ranger

Ultrasonic distance rangers measure distance by emitting pulsed ultrasonic waves and listening for the echo from a distant object. These are sometimes used in cars to aid in detecting the distance of objects behind the rear bumper. The one shown in Figure 33 outputs a digital pulse whose pulse width varies with the distance from the target object.

Ultrasonic sensor model HC-SR04 — Figure 33. An Ultrasonic sensor, model HC-SR04. The sensor has two cylindrical transducers, and four pins at the bottom of the board, labeled from left to right: Vcc, Trig., Echo, Ground.

Temperature and Humidity Sensors

There are dozens of temperature and humidity sensors on the market, with many different interfaces. The one shown in Figure 34, the DHT22, is very popular because it’s simple to use, reliable with a long track record, and inexpensive. It uses a one-wire interface.

Figure 34. a DHT-22 temperature and humidity sensor

Speaker

A speaker is a paper or plastic cone mounted to a coil of wire. The coil is mounted next to a magnet. When a current is passed through the wire, it induces a magnetic field, which attracts or repulses the magnet. This makes the cone vibrate, and produce sound. The speaker shown in Figure 35 is an 8-ohm speaker.