Arduino - Dimmable LED

Dimmable LED

• this is the fifth project in my arduino tutorial.
• for this project we will control how bright or dim an LED is by using a PWM signal.

Introduction

• so far we have only dealt with basic digital signals, that is, the signal can only ever be either HIGH or LOW (1 or 0)
• to control how birght or dim an LED is, we will require an analog source, or something similar to analog.
  • in our case, we are not going to use analog signals, but something called a PWM signal.
• Pulse Width Modulation(PWM) is a way to mimic analog signals but using purely digital sources.
  • a PWM is created by outputting a square ware but repeatedly switching the signals from on (HIGH) to off (LOW).
    • the signal is turned on for a short duration, then turned off for a short duration, then turned on for a short duration and so forth.
    • the ratio of how long the signal is left HIGH vs how long it is left LOW is called Duty Cycle
      • duty cycle is a very important concept when it comes to PWM signals.
  • for more information on PWM and Duty Cycle, please see wikipedia here.

Materials

• materials needed for this projects are:
  • Arduino
  • BreadBoard
  • wires
  • (one) LED
  • (one) 220 ohm resistor

Circuit

the circuit for this project is fairly simple. here is the circuit diagram

Here is the circuit i built for this project

Things to note:

• we are using pin 6 for our PWM signal.
  • only certain pins on the arduino are set up to output PWM signals.you can check the table here to see a list of avaliable pins on each arduino board.
  • you can also look at the pin numbers on the arduino. pins with PWM capability are ususally marked with a ~

Code

here is a screnshot of the code for this project. as usual, the complete code can be found here.

things to note:

• interestingly,to output a PWM you do not need to use pinMode to set the pin as an output.
• analogWrite()
  • this writes a PWM signal to the given pin
  • duty cycle is controlled by giving a number between 0 (0% duty cycle) and 255 (100% duty cycle).
  • please see here For more on analogWrite()

Results, Conclusions,and Final Remarks

• if all went well, you should have an LED which slowly gets brighter then turns off before slowly getting brighter again.
• PWM signals can also be used to control the speed of DC motors.

More to do

to continue on with this project, here are some more things to do:

• try using diffrent values for duty cycle and see the results.
• try changing the duty cycle and the delay times to get a smoother brightening of the LED
  • hint: it may help to add more calls to analogWrite() and delay()
• try making it so that instead of switching off after 100% duty cycle, the LED slowly dims back to being off.

Thank you for checking out my arduino tutorial. if you have any question, suggestions, or comments, please leave a comment below. And check back again for the next part of this tutorial.