The integrated circuits used in this project are uncommon today. It is worth the idea for a microcontrolled project or with equivalents. We found this configuration in an old documentation.
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...