This harmonic oscillator controlled by crystal was found in an American documentation of the 90's. The circuit uses transistors of the time. Current equivalents can be used.
Found in an Electronic Design from the 90's, this circuit uses common components. The circuit is...
When the sensor receives light, the relay closes its contacts and remains so even after the light...
This circuit produces pulses of 90 V at intervals that can reach 5 minutes. The circuit is from a...