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 uses two transistors and can be powered by just two small batteries. The frequency is given...
This circuit was found in the February 1985 issue of Radio Electronics magazine. It is based on an...
This circuit from Ferranti was released in 1969. It makes use of the company's transistors that admit...