This circuit triggers a relay when a light beam that hits the phototransistor is cut off. The circuit is from Electronics Now and the supply voltage depends on the relay voltage.
The circuit shown, found in a 2004 documentation, allows the use of a telephone, without the...
This simple circuit needs a high gain stage to compensate for losses. It consists of a passive tone...
The time constant for this circuit found in a 1973 publication is given by R and C. The shot is...