This circuit, to control air conditioning systems, was found in July 1984 Radio Electronics magazine. The circuit is for old types of the time that did not have microcontroller control.
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...