Found in a 1966 documentation, this “coin finder” uses components from the era operating at 2.1 MHz. The circuit uses an audio amplifier for detection.
This circuit monitors extra-low frequency (ELF) fields. We found it in an American documentation from the...
We can use any type of resistive transducer with central resistance in the range of 10 k ohms to 1...
This circuit controls two lamps so that when one increases in brightness the other decreases. The...