Relays are used to control high voltage loads, a signal of 5vdc can control a 230V load, with the help of relay circuit. In this video I am showing 4 relays circuit assembled on general purpose PCB. Compoenent: General Purpose PCB: 1 No. 12vdc relay : 4Nos. UF4007: 4 Nos. NPN Transistor : 4 Nos. LED 3mm Red: 5. Resistors 15 KOhm: 4 Nos. Resistors 10 KOhm: 4 Nos. Connectors.