Arduino and a sn754410 motor driver

Hey guys, just a small question that i think i have the answer to but im not sure.

ooook, I am using a sn754410 motor driver with my arduino. I'm following the tutorial at It's working and i have it setup the same but i'm using a wall wart to power the motor.

The problem i'm having is that the motor is moving very slow. The wall wart puts out 22 volts dc (even tho it says 15 volts on it) and the motor is rated at 5 to 36 volts just like the motor driver. when i measure the voltage at the motor ends on the driver im only getting 5 volts.

Could this be caused by the fact that the wall wart is rated at 15 volts and 500mA? Are the amps too low and the volts are dropping when it runs into the driver?

Any help will be greatly appreciated.

well, are you powering the motor driver from the 5 volt arduino supply?

If you follow the wiring on that site it will only give you 5V on the motor. You need to connect Vcc2 to the 15v external supply and Vcc1 to the 5V arduino supply.

I have it wired just like the site but I do have the 15v supply connected to Vcc2 and 5 volts on Vcc1 from the arduino. I've done this in the past just fine but on batteries. The only thing that's changed is the wall wart

So if you measure the voltage at the motor as 5V what do you measure at Vcc2 at the same time as the motor is on. If this measures 5V also and then goes to 22V when the motor is off then it is indeed the wall wart not being able to delver the current.

ok i get 20 volts at vcc2 when the motors running.

That is odd. Seeing 20V on Vcc2 means that the power supply is OK. So the only thing I can thing is that you haven't got it wired up like you think or you have a faulty 754410.

The thing to try is to see if the other outputs are behaving like this. Connect resistors say 1K to the other outputs with the other end to ground. Then switch them then see you get 0v and 20V across it. Then connect the resistor as if it were the motor, that is each end to an output and measure it. If you haven't been using the other outputs then they should be OK. If not then seriously look at the wiring and the way round you have the chips. Pay particularity attention to the ground connections.

Thanks for the help Grumpy_Mike. I'll look over it again tonight. I'm starting to think the grounds are having problems. I'll check the other side too.