With this circuit it is possible to use a frequency meter as a tachometer. The circuit was found in American documentation from the 90s. The phototransistor can be of any type.
This SCS counter circuit was found in a 1964 General Electric documentation. The circuit has a...
This 1 to 40 MHz amplifier is from a 1969 Motorola documentation. The components are of the time...
The figure shows how to implement an R-S flip-flop or bistable reset-Set with an LM3900...