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.
We found this circuit in an American documentation from the 60's. The transistors are made of...
The accuracy of this circuit depends on adjustments made with capacitors of small tolerances of known...
The figure shows how to implement an OR function with two inputs, using a relay. The relay...