Using the LM358 from Texas Instruments, this circuit uses LED indicators and can be powered with voltages of 5V or according to the analyzed logic.
I found this circuit in a 1986 English magazine. It can still be easily assembled, exchanging Q1...
We found this circuit in an Argentine publication from the 70s. The coil can be made with 80 turns...
Found in General Electric documentation from 1967, this circuit makes use of an unusual...