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 circuit was found in an American documentation from the 60's. The transistors are from the...
This oscillator is indicated for the adjustment of FI of FM radios, having its frequency...
This configuration triggers an external circuit or simply an LED for time given by R1 and C1 (T =...