I am using an ESP8285 to make my own wifi relay device. I am using an ULN2003A to drive the relays, I have the 5V relay coil voltage connected to COM and the other coil connected to the output of the ULN2003A. When I send a logic high to the input of the ULN2003A the output should go to logic low and turn on the relay but it is not going to a logic low. It only drops from about 4.98V to 4.18V which is not low enough to turn on the relays. I am not sure why it is not going to logic low when I give a logic high input. I have added the schematic I am using, I apologize if the pic is a little blurry.
Best Answer
You have the diodes backwards, which will likely damage the ULN2003A and the diodes. They are supposed to be reverse-biased when the relay is energized.
You also don't need them, there are diodes in the ULN2003A, which you have correctly connected to +5V via the COM pin (well, it will reduce the loop area a bit if the diodes are very close to the relay, so they're not entirely useless).
It would be a bit more clear if you followed convention in drawing the schematic and had the supply rail at the top.