Arduino Function Generator: Square Wave with Variable Duty Cycle

A beautiful but expensive piece of electronic test equipment

Hi! Not everyone can afford the $2000 for a beautiful function generator like this Agilent 33210A, but everyone deserves to have basic function generation capabilities. So, today I’m going to show you how to make a basic function generator using everyone’s favorite microcontroller: an Arduino Uno!

In this post I’m going to go over some basic code, and how to set up an LED to test it out.

Hardware setup

Set up the LED+resistor with positive lead in pin 9 and the negative plugged into ground. Plug the Arduino into your computer.

Yes, I have a genuine Arduino, but knockoffs are fine too! Preferable, even, cause you can break them without feeling bad.

We’ll start with the basics:

Square Wave Generator, 50% Duty Cycle

To use this, just change blinkrate to whatever frequency you’d like the pin to output.

If we just changed after 1 sec/blinkrate, we’d get a square wave of blinkrate/2 Hz. So without using delay, we change the LED after 1 sec/blinkrate/2, since we need to account for both an on and off period. Using LED_state, we track whether the LED is on or off, so we don’t have to worry about if statements and all that jazz.

However, this code is limited, since it only has a duty cycle of 50%. What if we want the LED to be on more than half the time during a cycle?

Duty Cycle

From Wikimedia Commons

Duty cycle is the ratio of on-time to off-time during one cycle of a wave. In the past, it was also called the light-dark ratio, which is a little more intuitive.

To make a wave of n% duty cycle, we can split each cycle of our original function into 100 little pieces, then keep the…