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.
Found in a Popular Electronics from 1992, this circuit uses a PLL567 in an audio meter bridge that...
This circuit was found in an old European documentation. When R2 is cut off the circuit triggers...
This circuit for the positive front of a rectangular signal was found in an old documentation, but applies...