Found in an ancient American documentation, this circuit can generate signals up to 40 MHz for a Z80, microcontroller widely used at the time. The circuit must be powered with 5 V and also serves as a shield.
This circuit adds a beep to turn on with car flashers that do not have this feature. A 47 ohm to...
This 80's circuit uses a small light bulb as an indicator, but an LED with the appropriate resistor...
This circuito from the 1977 GE Semiconductor Manual circuit provides timings from 0 to 90 seconds...