Simple variable square wave generator?

Thread Starter

Al Vince

Joined Feb 24, 2015
Hello, I was wondering if anyone had any suggestions with a simple circuit I am looking to build for a project. I would like to make the circuit as small and simple as possible. I will be using a quality regulated power supply for the input.

- DC input 14volts
- DC output a square wave adjustable up to 12 volts at 1.5A
- Use a pot to adjust frequency output between 30hz to 100hz
- Use a pot to adjust voltage output between 6 volts to 12 volts
- Use a pot to adjust duty cycle output between 10% and 100%

So for example.... say I can set the pots to output at 60hz - 9 volts - 30% duty cycle.

Any help in pointing me in the right direction... maybe there is already a schematic or sample design I can use or modify? I am not an engineer, just a hobbyist.

Thanks in advance!


Joined Aug 1, 2013
A single 555 chip can give you 10% to 99% duty cycle control with only one pot. Or, it can give you a 3.3:1 frequency range control with only one pot. But I don't think it can do both at the same time with one pot for each variable. Two 555's in series can.


ian field

Joined Oct 27, 2012
use a 555 timer and tda2030 amp

The TDA20xx family of audio amplifiers are very similar to power op-amps - of which there are quite a few to chose from.

Its not *THAT* difficult to wire them up as a square wave generator and save the 555.

There's probably an example in the NS appnotes collection - they have several LMxxx parts that are almost identical to the TDA20xx ones.

A simple 2 transistor astable can be made variable frequency by commoning the base resistors to a pot that feeds them Vcc - that uses more components than the 555 option, but the output stage can be as simple as a complementary pair of emitter followers.