We found this version of the automotive tachometer in a 1980s publication. Variations from other sources appear elsewhere in this section. The indicator is a 0 to 1 mA milliammeter.
The circuit is from a June 1995 Electronics Now. The relay is power-dependent and both R1 and R2...
This circuit for several frequencies was obtained in an American documentation from the 90s. The...
The circuit shown in the figure is suggested by AllegroMicro (www.allegromicro.com) and consists of an...