I am designing a IR base home light control. for this i use 6 relays and i try to driver it through uln2003. I connect the GND and COM wire with 12 volt power supply and input pins are connect to microcontroller which gives 5 volt supply but OUTPUT will become constant (about 1 to 1.5 voltage) and not change on any logic 0 or 1
The circuit below takes into account the open collector operation of the ULN2003. The diode D1 is to prevent kickback when deactivating the relay. Technically this diode is built into the ULN2003, but it never hurts to have an extra!