We found this circuit in the Radio Electronics magazine of February 1993. The main integrated circuit is from that time and the power supply is made with voltages of 6 to 15 V.
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...