This circuit is from 1980s documentation. The maximum operating frequency is 3.5 MHz. The current of the LED can be from 0 to 100 mA. The integrated circuits used are from that time.
We found this simple protection with zener diode in a 1967 Motorola documentation. The zener diode...
This triac circuit was found in the October 1987 Radio Electronics magazine. The triac is...
This circuit triggers a buzzer or other warning device when the light falling on the sensor is cut...