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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

Project Source on GitHub Project Gallery Return to the LEAP Catalog

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. Two main themes have emerged in recent years, sometimes combined:

  • electronics - 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
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.