Introduction
In this lab, you’ll control a servomotor’s position using the value returned from an analog sensor. Servos are the easiest way to start making motion with a microcontroller. Even though they don’t turn 360 degrees but only 180, you can use them to create all sorts of periodic or reciprocating motions. Check out some of the mechanisms at Rob Ive’s site for ideas on how to make levers, cams, and other simple machines for making motion.
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:
- What is a Analog Input with Arduino
- What is an Arduino Library
Things You’ll Need
Figures 1-8 below are the parts you’ll need for this exercise. Click on any image for a larger view.
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 9 and 10.
Figure 9. 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.
Figure 10. An Arduino Nano mounted on a solderless breadboard. 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
Connect an Analog Input Sensor and a Servo
Connect an analog input to analog pin 0 as you did in the Analog Input Lab covered previously. A force-sensing resistor is shown in Figure 11-13 below, but you can also use a potentiometer, phototransistor, or any analog input you prefer. Then connect an RC servomotor to digital pin 3. The yellow wire of the servo goes to the pin, and the red and black wires go to +5V and ground, respectively. Related video:Intro to Servo Motors
Note: Most RC servomotors will run on as low as 3 volts, even if they are rated for 4-6 volt input.
Safety Warning! Not all servos have the same wiring colors. For example, the Hextronik servos that come with Adafruit’s ARDX kit use red for +5V, brown for ground, and mustard yellow for control. Check the specifications on your particular servomotor to be sure.
Figure 13. Breadboard view of a servomotor and an analog input attached to an Arduino Nano. 3.3 Volts (physical pin 2) and ground (physical pin 14) are connected to the voltage and ground buses of the breadboard as usual. A force-sensing resistor, or FSR, is mounted below the Nano, in in rows 22-23 of the left center section of the breadboard. a 10-kilohm resistor connects one leg of the FSR to the left side ground bus. A blue wire connects the row that connects these two to analog in 0 on the Arduino Nano (physical pin 3). A red wire connects the other pin to the left side voltage bus. The servomotor’s voltage and ground connections are connected to the voltage and ground buses on the right side of the breadboard. The servomotor’s control wire is connected to pin D3 of the Nano (physical pin 21).
When you attach the servo, you’ll need a row of three male headers to attach it to a breadboard. You may find that the pins don’t stay in the servo’s connector holes. Put the pins in the servo’s connector, then push them down on a table gently. They will slide up inside their plastic sheaths, and fit better in your servo’s connector. Related video: Connect the Servo. Figures 14-16 show steps of this in action.
Program the Microcontroller
First, find out the range of your sensor by using analogRead() to read the sensor and printing out the results.
void setup() {
Serial.begin(9600); // initialize serial communications
}
void loop()
{
int analogValue = analogRead(A0); // read the analog input
Serial.println(analogValue); // print it
}
Now, map the result of the analog reading to a range from 0 to 179, which is the range of the sensor in degrees. Store the mapped value in a local variable called servoAngle.
void setup() {
Serial.begin(9600); // initialize serial communications
}
void loop()
{
int analogValue = analogRead(A0); // read the analog input
Serial.println(analogValue); // print it
// if your sensor's range is less than 0 to 1023, you'll need to
// modify the map() function to use the values you discovered:
int servoAngle = map(analogValue, 0, 1023, 0, 179);
}
Finally, add the servo library at the beginning of your code, then make a variable to hold an instance of the library, and a variable for the servo’s output pin. In the setup(), initialize your servo using servo.attach(). Then in your main loop, use servoAngle to set the servo’s position.
#include <Servo.h> // include the servo library
Servo servoMotor; // creates an instance of the servo object to control a servo
int servoPin = 3; // Control pin for servo motor
void setup() {
Serial.begin(9600); // initialize serial communications
servoMotor.attach(servoPin); // attaches the servo on pin 3 to the servo object
}
void loop()
{
int analogValue = analogRead(A0); // read the analog input
Serial.println(analogValue); // print it
// if your sensor's range is less than 0 to 1023, you'll need to
// modify the map() function to use the values you discovered:
int servoAngle = map(analogValue, 0, 1023, 0, 179);
// move the servo using the angle from the sensor:
servoMotor.write(servoAngle);
}
Related video: Code for the Servo & Turn the Servo
Get Creative
This is just a suggestion for a short project. It’s not a requirement for the class homework.
Servo motors give you the power to do all kinds of things.
They can be used to push a remote control button, in a pinch, as shown in Figure 17.
You can play drums like in this Project by Nick Yulman. You can build a frisking machine like in this Project by Sam Lavigne and Fletcher Bach.
If you’ve got 800 or so of them and a lot of time, you can build a wooden mirror like this Project by Daniel Rozin
Come up with a project of your own that needs a little movement, and see if you can solve the problem with a servomotor.