This series and parallel sensor circuit was found in Popular Electronics from the 1990s. Any SCR can be used and the supply voltage depends on the load.
This simple photometer uses a 1 mA milliammeter and a common phototransistor. The circuit has its...
The circuit of the figure allows to implement a multimeter of high sensitivity or even to use a...
This simple circuit must be powered by a voltage of 5 V. The integrated circuit is the 7400, but...