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Digital Input and Output with an Arduino
In this lab, you'll connect a digital input circuit and a digital output circuit to a microcontroller. Though this is written for the Arduino microcontroller module, the principles apply to any microcontroller.
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For this lab you will need the following parts:
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 and any of the ground connections:
Add a Digital Input (a switch)
Connect a switch to digital input 2 on the Arduino. The switch shown below is a store-bought momentary pushbutton, but you can use any switch. Try making your own with a couple of pieces of metal.
Add Digital Outputs (LEDs)
Connect a 560-ohm resistor and an LED in series to digital pin 3 and another to digital pin 4 of the Arduino.
What happens if you don't include the resistor connecting the switch to ground?
A note on resistor values: if you don't have a 10-kilohm resistor for the switch, you can use any reasonably high value. 4.7K, 22K, and even 1 Megohm resistors have been tested with this circuit and they work fine. As for the resistor on the LED, the higher the resistor value, the dimmer your LED will be. So 220-ohm resistors give you a nice bright LED, 1-kilohm will make it dimmer, and 10K or higher will likely make it too dim to see.
Program the Arduino
Connect the microcontroller to your computer via USB. When you plug the Arduino into your computer, you'll find a new serial port in the Tools-->Serial Port menu (for details on installing the software, and USB-to-serial drivers for older Arduino models, see the Arduino Getting Started Guide). In OSX, the name will begin with /dev/tty.usbmodem- if it's an Arduino Uno later, and /dev/tty.usbserial- if it's a Duemilanove or earlier. In Windows it will start with COM like all the other serial ports.
Write a program that reads the digital input on pin 2. When the switch is pressed, turn the yellow LED on and the red one off. When the switch is released, turn the red LED on and the yellow LED off.
In your setup() method, you need to set the three pins you're using as inputs or outputs, appropriately.
In the main loop, first you need an if-then-else statement to read the switch.
Once you're done with that, you're ready to compile your sketch and upload it. Click the Verify button to compile your code. Then click the Upload button to upload the program to the module. After a few seconds, the following message will appear in the message pane to tell you the program was uploaded successfully.
Binary sketch size: 5522 bytes (of a 7168 byte maximum)
Press the switch and watch the LEDs change until you get bored. That's all there is to basic digital input and output!
This is just a suggestion for a short project. It's not a requirement for the class homework.
Many projects can be made with just digital input and output. For example, a combination lock is just a series of switches that have been switched in a particular sequence. Consider the cymbal-playing monkey below:
His cymbals can be turned into a switch by lining them with tin foil and screwing wires to them:
Come up with your own physical interface for a combination lock.