This windshield wiper timer was obtained in an 80's Hands On. The transistor can be the BC548 and the relay is 12 V sensitive. The time is set to R3.
This circuit is from a Popular Electronics from the 90s. Its gain is 22 dB and can be used as a...
This circuit was found in an article in Radio Electronics magazine from October 1962. At that...
This circuit can be implemented with other operational amplifiers. The formulas for calculating the...