The circuit presented was suggested by Texas Instruments in an opto-electronics manual. The transistor can be the BC548 and the supply voltage depends on the application.
In this circuit the relay triggers on when light falls onto the sensor, a common LDR. Power supply...
This circuit with the 555, was obtained in a 90s American documentation. The signal must be...
This project makes use of a technology without many digital components and that can be easily...