This detector with ultra-low deviation was found in an American documentation from the 90s. Operational amplifiers are from that time. The power supply must be symmetrical.
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...