Ok, I'm trying to control a stepper motor (link) through a ULN2004 transistor array. I'm following the circuit diagram on this page, the 4-pin one since mine has 4 coil wires and two common wires. From what I can gather, the white and yellow wires should be common, and the black, red, green, and blue wires are powered in that order to rotate the motor. Originally, I thought it should go black-green-red-blue, but when I manually powered it in that order, it didn't work. When I go black-red-green-blue, I can feel an even rotation in one direction. When I have the yellow and white to +12v, the other four in 16, 15, 14, and 13, (of the array, not the arduino) and gnd of the transistor array connected to the negative battery pole, it functions as expected, sort of. I can connect pins 1, 2, 3, and 4 of the array to +12v sequentially, and each successive coil in the motor activates. The problem is that when I connect the common pin of the array to +12v, as in the diagram, the motor locks up, which I assume means that all the coils are active. My first thought was that perhaps the arduino has to pull each pin successively down to ground to activate that coil, but with pins 1, 2, 3, and 4 all connected to ground, nothing changes. Throwing caution to the wind, I plugged them all to +12v, but still no dice. The other strange thing is that with the common pin disconnected, I can activate each coil by powering pins 1, 2, 3 or 4 to +12v, but connecting one of them to +5v on the arduino does nothing. I thought this transistor could be activated by 5v, no? Anyway, as it stands, I suspect the fault lies with my inadequate understanding of transistors and/or stepper motors. Any help would be greatly appreciated.
You must get the connections correct and only a few of the possible combinations work. Use an ohm meter to figure out which are the common connections and then swap the remaining ones on the driver output terminals. ALWAYS turn off the power when you change connections, or you may destroy the driver. See this site for all the info you need: http://homepage.cs.uiowa.edu/~jones/step/
InventiousTech: Ok, I'm trying to control a stepper motor... Throwing caution to the wind, I plugged them all to +12v, but still no dice.
How/Where does that make any sense?
InventiousTech: Any help would be greatly appreciated.
ULN2803 pin 9 = ULN2003 pin 8 ULN2803 pin 10 = ULN2003 pin 9
"Robotshop" is calling that Unipolar, but it is wired such that it can be configured for either Unipolar or Bi-polar operation.