Found in a Popular Electronics from the 80's, this circuit makes use of a time integrated to control a relay in a timed way. R2 determines the activation time.
This is the basic configuration of an operational amplifier sample & hold circuit. The FET and...
The integrated circuit 4136 consists of operational amplifiers of type 741 in the same enclosure and...
We find this circuit in a 1987 publication. It makes use of comparators constructed around the 741...