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Project Notes

#230 MinimalLCOscillator

Test an LC oscillator of just 5 components


I borrowed this idea and circuit design from stoneslice’s 1MHz Oscillator video.

I’m not sure how the circuit fits into the taxonomy of oscillator circuits, but it is similar to a Colpitts oscillator circuit - but one capacitor is replaced with a resistor.

I tried a range of component values on a breadboard. To sustain the oscillation, I found I had to increase the value of the resistor - 4.7kΩ proved good for all cases.

L C frequency
470µH 47pF 1.6MHz
150µH 47pF 2.9MHz
470µH 68pF 1.5MHz
150µH 68pF 2.7MHz

The effect of the resistor seems to alter the resonant frequency of the “impure” tank circuit. For example, I’d expect with 150µH/47pF the frequency to be 1.89MHz when in fact I measure 2.819MHz.

Nevertheless, an interesting self-oscillating circuit.

Soldered on a PCB with 150µH/47pF and a J201 n-FET, there are no issues sustaining an oscillation, however the frequency is not particularly stable and there’s a distinct second harmonic.





The Schematic

The Build

Credits and References

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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. 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.