Hello friends, I hope you are doing well. In the previous tutorial, we studied the working principle of a relay . Today, we will connect a 12 V relay to a PIC18F4550 microcontroller through a ULN2003A driver. A relay coil needs more voltage and current than a microcontroller pin should provide. It is also an inductive load, so it produces a voltage transient when switched off. The ULN2003A solves these interface problems by providing seven low-side Darlington drivers and seven internal clamp diodes in one package. The key point is that the ULN2003A does not convert a 5 V logic signal into a 12 V output. The 12 V energy comes from a separate 12 V supply. A logic high merely turns on one internal driver, which connects the low side of the relay coil to ground. We will examine that current pa ...