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Does anyone know how to build a push/pull oscillator or a similar square wave oscillator?

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The simplest oscillator is just an inverter connected back to itself, but that's too trivial to be an answer. – endolith Sep 29 '10 at 19:23
I would like a nice square wave – Nate Zaugg Sep 29 '10 at 19:26
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@endolith: that would not work. An inverter connected to itself will usually not oscillate, but instead stabilise and waste power. Instead you will need at least 3 in a ring configuration. – Thomas O Sep 29 '10 at 19:43
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@Thomas: Ok, ok, a Schmitt-input inverter. :D electronics-tutorials.ws/logic/log16.gif – endolith Sep 29 '10 at 19:45

4 Answers

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One Schmitt-trigger inverter (74LS14) together with an RC circuit feeding it will do a pretty good job of creating a simple oscillator. Adjust the RC time constant to adjust the frequency.

Schmitt-trigger oscillator

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I think that produces a nice sawtooth wave, which might be good enough. – Nate Zaugg Sep 29 '10 at 21:16
You only need one Schmitt-input inverter, as I linked above, and it should produce a square wave, not a sawtooth. The input of the inverter will be a sawtooth, but the output will be a square. electro-tech-online.com/attachments/… – endolith Sep 29 '10 at 23:16
For some reason in college we chained a few of them together. It might be that we didn't use the RC circuit to create a delay at the time and were instead relying on the propagation delay of each of the gates. I edited my answer. – mjh2007 Sep 30 '10 at 12:46
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I'd use a 555 Timer in an astable configuration feeding a D-type falling edge triggered flip-flop.

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The Kalitron is the classic push-pull oscillator. They aren't used much these days, but were quite popular at one time in the valve era, often using a double-triode valve.

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Going more basic, a positive feedback OP-AMP circuit can be used to build a square wave oscillator.

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