The main feature of this circuit found in an old American publication is that it is powered by the very signal it converts. The transistors are of the time and can be replaced by current types.
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...