In the figure we have the way to control a flip-flop with the 4069 from positive pulses. The circuit can be used as a shield, if powered by 5 V.
The circuit shown is from the National Semiconductor Linear Applications Handbook of 1994. using...
This blocking oscillator configuration was found in a 1964 American book. The circuit can be...
When light fails to focus on the sensor, a common photo-transistor, the relay closes its contacts....