#049 BJT RC Oscillator
Demonstrates a simple RC/transistor multistable vibrator
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.