problems using a ULN 2003

hello I was using a ULN2003 to drive 6 dc motors just on and off with the arduino I was using two power adaptors at 7,5 volts but when I change the adaptors to 9 volts just to give speed to the motors the arduino goes crazy. Any help will be more than apreciatted. thanks

Several things come to mind.

You state that the motors are rated for 6 volts, but you’re trying to run them on 9 volts?

I think your first clue may be right there. Trying to run at 150% of nominal is really pushing it!

A DC motors current draw rises as voltage increases. Are you sure you aren’t exceeding the ULNs power rating?

Pushing a DC motor beyond rated RPM also will also dramatically increase the amount of commutation noise, and increase the rate of wear on the commutators.

I would consider using a higher RPM motor, but if you must proceed with this, here are a couple tricks that may help, up to a point.

Solder a capacitor directly to each motor, right where the wires enter the motor. Keep the caps leads as short as possible. Use a cap with a voltage rating of 600 volts or so (yes, the commutation noise can easily reach hundreds of volts). Use a ceramic, non polarized type.

This cap will not only help keep the noise down, but will also help extend the life of the commutators.

Insert a balanced choke between the motor supply and the motors. This will help keep commutation noise from feeding back through the power supplies to your Ardy. (Yes, the noise will pass back through both supplies)

Make sure that the connections from the motor supply to the ULNs ground and diode pins are low resistance. Ideally, you will feed the ULN first, then the motors.

Make sure that the motor supply and Ardy supply have only 1 ground point in common, and make sure that point is as close to the the ULNs ground pin as possible.

Do not in any way shape or form connect the positive supplies together.

Another possibility: if the 9V adapters are rated for less current than the 7.5V ones, the load of the motors may be causing the voltage to sag (if they're unregulated), or shut down (if they are regulated).

Try putting an LED on the Arduino's 5V supply, with a resistor that limits it to 5mA or so: it's likely that you'll see it flickering because the power supply is flaking out.


thanks for the ideas. I "did connect "the positives toguether and fried the arduino I am going to try again. Actually I did not explain well about the motors they are motors that are supposed to receive 12 volts but I always was running them at 6 to low down the Rpms but I am trying to increase them and run them at 9volts. Another thing that is happening is yes the power adaptors are regulated and when the last one enters in contact shuts down the rest. probably is a problem with that adaptor also. one last question sorry about my english what is a " balance choke between the motor supply and the motors" and also wich kind of resistor will limit the 5volts out of the arduino to 5ml a regular 220 ohm will do? thanks

Look at this link:-

make sure you don't over stress the drivers:-

Also you need a protection diode as explained in the link. Decoupling is good as well see this link:-