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Project Notes

#668 Code Practice Oscillator

Build and test a simple 2-transistor code practice oscillator.


Here’s a quick demo..



There’s a long history of simple audio oscillator circuits intended to practice morse code.

Some of the circuits found on the internet are from the very early days of vacuum tubes or early transistors. I’ve tried to make a few of those circuits work with little success, and suspect many are no longer a practical designs because of how good our components are these days. A couple of examples…



Circuit Design

The circuit I’ve used here - that does work - is based on Simple Two Transistor Oscillator (

I’ve modified some of the values for a tighter audio range. At 5V it is very loud;-)





Here’s a trace of the oscillator output with R1 in a random mid-position, pitching it at 415Hz. As can be seen, the oscillator is a pretty harsh for an audio tone:

  • square wave
  • unbalanced duty cycle
  • appears to be quite a flyback voltage spike


Credits and References

About LEAP#668 BJTRCOscillators
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This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects, usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting (IMHO!).

The projects are usually inspired by things found wild on the net, or ideas from the sources such as:

Feel free to borrow liberally, and if you spot any issues do let me know. See the individual projects for credits where due. There are even now a few projects contributed by others - send your own over in a pull request if you would also like to add to this collection.