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Project Notes

#049 BJT RC Oscillator

Demonstrates a simple RC/transistor multistable vibrator

The Build

Here’s a quick video of the circuit in action:



This oscillator is based on coupled RC circuits with associated switching transistors.

The frequency of oscillation is given by

f = 1/(ln(2) * ( R1 * C1 + R2 * C2))

Or in this case with 22kΩ and 22μF, that means about 1.5 Hz.

Note that for the oscillation to work correctly, the components need to be well matched. The first two transistors I stuck in the circuit produced a significantly uneven oscillation. Replacing the transistors with some newish S9013 NPN transistors fixed the problem, and to the human eye at least the circuit now runs completely balanced.

NB: I’m using S9013 but any small-signal NPN transistors will do.


The Breadboard

The Schematic

Credits and References

About LEAP#49 BJTRCOscillators
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This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is my personal collection of electronics 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.