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 simple trigger circuit was found in a 90’s American documentation. The integrated circuit is...
This sensitive circuit was found in the August 1971 issue of Radio Electronics magazine. The SCR...
The varactor or varicap diode tunes the signal for listening to SSB signals on a common receiver. The...