We found this transistorized circuit in a 1985 documentation. The circuit can operate with voltages from 9 to 12 V and the adjustment of the operating point or input sensitivity is done in P1.
The figure shows how to implement an alarm buzzer in an LM3914 to warn about crossing the scale...
This circuit can act as a shield being controlled by a microcontroller by pin 1 or 2. The...
This circuit was obtained from a 1980's QST magazine. The circuit can generate 1 to 15 MHz signals...