My design is a remote controlled car. I took a play station controller gutted it and put my own momentary switches in there. When I click a button, the momentary switch connects ground to the circuit and that flags my microcontroller. My microcontroller reads the ground on portC and knows that means we have a button press (after debouncing program confirms). The microcontroller then sets port B to high which is about 5 volts with about 10-20 mA or so. My problem is I can't run a motor with a current that small. So I tried using a ULN2803A to increase the current from portB but that doesn't seem to be working. I did a little research and read that you need to have a relay connected to the output of the darlington pair. I have never used a relay and do not know what it does. Can anyone send me a diagram or a little info on how to get a 500mA output out of the ULN2803A. Ive been trying to figure this out forever by myself and now I'm submitting for help so pleassse do help. thanks and let me know if you need any more information to answer my question properly.

Peter

 

Just hook it up like this

 

Wow thank you so much be80be I had been struggling with this configuration forever. That schematic was simple and clear and now it runs like a charm. I should have known that the motor is an inductive load and therefore needed to hook up the com terminal. Correct me if i'm wrong on the dc motor being an inductive load. I have one question though why does the motor need to be connected to Vcc of microC. I want to understand exactly why its working so I don't need to go through this again haha. thanks again

 

The ground are tied because you using the micro controller to switch the ULN2803A.

If not tied your 5 volt to B1 would look like 0 to ULN2803A