This 3 and-a-half digit circuit was found in a Teledyne documentation from the 90s. The circuit uses a thermocouple as a sensor. The integrated circuit used is uncommon today.
Circuits like this one, using the LM386 audio amplifier, are available from other sources in this...
This bass and treble control only attenuates the corresponding signals, requiring further...
Using a large inductance, this circuit was found in a Popular Electronics from the 90s. The...