Found in American documentation from the 1980s, this circuit uses transistors from that time. It generates increasing and decreasing tones when we press and release the push button.
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...