This circuit uses a resonant reed switch at the trigger frequency. The circuit is from General Electric in a 1966 documentation. This type of component is rare today.
This circuit with the ICL8068 was taken from an article in the February 1981 Radio Electronics magazine....
The National Semiconductor operational amplifier, now owned by the Texas Instruments group, is no...
The Motorola MOC501O optocoupler has a complete amplifier inside the sensor, enabling the...