This is the circuit for the HM-10ª, an instrument sold by Heathkit. The circuit is from a Radio Electronics from May 1963. The indication is by an analog instrument.
Found in a 1966 documentation, this “coin finder” uses components from the era operating at 2.1...
This filter operates in the “opposite” way to the previous one (CIR8814), cutting all signals...
In the figure we have the way to use a stepper motor as an encoder. Operational amplifiers can be of...