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.
This circuit is indicated to operation with low intensity sources such as electret microphones and...
Suggested by General Electric in a 1965 publication this circuit uses a light bulb. Can be changed...
Found in Popular Electronics from the 90s, this circuit has LED indicators that show when the...