This circuit is from an American manual from 1975. The transistors are types of the time, but equivalents can be used, as well as the relay that can be according to the supply voltage.
This circuit was obtained from a Radio Electronics in May 1967. The circuit consists of a system...
This simple two-transistor capacitance meter uses a 50 uA microammeter as an indicator instrument. The...
Found in a European magazine from the 90s, this circuit emits beeps that are several seconds apart to...