This circuit was found in Radio Electronics magazine from October 1964. The circuit uses two transistors of the time that require a supply voltage of 9 V. Consumption is 2.5 mA.
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...