This triac circuit turns on a load after a time of 8 to 80 seconds adjusted by potentiometer R7. The circuit is from a Radio Electronics from June 1970.
We find this circuit in an American 80's documentation. It makes use of IC sensor which is mounted...
This is a configuration obtained from an old manual, using an operational amplifier of the time....
In the figure we have the way to add hysteresis to an operational amplifier. The relationship...