Unipolar Stepper controller problem (ULN2308A)

Projects General Guidance
1

Hello everyone,

So, not very new to the Arduino, yet still a noob in electronics, yesterday I tried to put together a simple Stepper motor driver, the stepper itself being a Velleman ST35 (6 wire), which I should have never have bought in the first place seen there is, to my knowledge, no Datasheet whatsoever available... Anyhow, I have no idea how, but I blew everything up, I mean, the ULN just went poppoppop... with a load of smoke and I'm pretty sure I blew out the Arduino's USB port, can't upload anything : error : programmer is not responding.. Now the thing is, I'm not sure why everything blew (I do know it's not going to be a cheap mistake and I'm kind of pissed, but tis my fault most likely probably definetly.. )..

So here are my questions :

  1. How is it possible that the Arduino drew the leftover electricity out of my laptops battery in a matter of seconds? Would it be possible to prevent this from happening in the future (Not the first time)...
  2. Not sure what went wrong, maybe one of the COM leads wasn't plugged in correctly, but still not sure how all this went down..
  3. How could the 12V battery be responsible for burning out the ULN2803, could the lack of resistors be responsible, is there not a 2.7K resistor built in?
  4. Could it be a malfunctioning Arduino in the first place? It has always been a little faulty, reset button failed etc..

I'm such a noob in electronics, I admit, so no need to point that out.
I had tried the circuit just before with LEDs and resistors, everything worked fine transistor wise, then changed them out for the motor and BOOM..

So I was using an Arduino Uno, ports 5, 6, 7, 8, 9 and 10...
A UL.N2803A..
A 12V2Ah rechargeable Lead-Acid battery..
A couple of connectors..

2

I've used the L298D half bridge before with a couple of DC motors, eventually ended up pulling way to much out of my computer's usb ports causing it to shut down although it's battery is present and cable is plugged in.. Luckfully haven't really damaged my computer, yet...

3

Hmmm, the battery in cycle use is supposedly regulated at 14.4 - 15.0V with an initial current of 0.6A MAX..

4

There are two likely reasons for the catastrophic failure, assuming that the rest of the circuit was correct to begin with:

  1. The battery was accidentally connected backwards

  2. The motor draws too much current for the ULN2308, so it overheated and shorted internally

Either of those situations could have led to damage to the Arduino. It is never a good idea to use parts for which you don't have a data sheet or can't characterize thoroughly, out of the intended circuit. For a motor, one essential piece of information is the resistance in ohms of the motor windings or the stall current. Then you can choose an appropriate motor driver.

5

Testing the ULN seemed to work fine with simple LED's so I'm guessing the second solution is the more probable... Thanks, and I guess I can only advise to not buy components without proper datasheets..