Hey guys,
I got a question for ya.
I was looking at the circuit for a stepper motor:
And I noticed the 4 pin version of the circuit is really similar to the circuit I'm building to control an array of LEDS:
Hi Res: http://raccoonrocket.com/gb/egbschematic-final.png
With the main difference being that I don't have anyhting connected to Pin 10, which is Com on the 2803A.
Now, as stated in this thread by GrumpyMike, connecting something to that pin isn't necessary with my LEDs:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1269283709/7
But I know that with the motor it is necessary because... well I don't remember the term for it, but when the magnetic field collapses in the motor it creates a high voltage spike, and connecting the positive lead of the power source for the motor to that Com pin (which on my darlington IC is pin 10) will protect my circuit from those spikes. Somehow. I think.
Anyway, so I've got this circuit here, which is the PCB version of the shcematic above with a few modifications. (Shifted the column pins down by one so I could make everything nice and neat, changed a few resistor names to better match the components they go with, added a potentiometer for volume control, and added support for dual 9v batteries in a parallel config.)
Hi Res: http://raccoonrocket.com/gb/egbpkecircuit.png
And I guess this circuit is fine without that pin 10 connected on the 2803A.
But I'm making another circuit, almost identical to this one. One where I'd like to have the option of controlling a unipolar stepper motor with four pins.
The other circuit will have no LED array. Instead, those 8 row pins will be connected to 8 leds which go directly to ground. And the column pins... four of those would be connected to my stepper motor. The other four... I'd like to leave my options open for. Maybe connect some more leds to them.
So my question is this...
Presumably, I want to connect the motor directly to my battery's positive lead, which is +9v. I also want to connect pin 10, aka Com, to +9v as well.
But what if I also want to put some leds on some of those pins. And I want the leds to go to +5v on the arduino for whatever reason, via a resistor.
Will that even work? Or is sinking +5v on some of the pins of the darlington array, and +9v on others, a no-no?
Also, let's say that instead of running a stepper motor, I want to run a servo. To run a servo, I suppose I need to connect the power wire to +9v, and the ground wire to ground... but then there's the signal wire. I'm pretty sure I can't hook that up to the darlington array. That's gotta be pulsed high by the servo lib right? And my darlington array will only pull pins low. So I can't use the same connection for
the servo and the motor.
If I want the option to connect a servo then, and I want to use those same pins the darlington is on, then I guess I gotta have some pads in there on the traces between the arduino and the darlington, to which I'd connect the servo signal wire. I assume that would effectively bypass the darlington array, since while the traces would still go to the inputs, I wouldn't have anything on the outputs for those pins particular pins.
At least that's the theory. What I'm unsure about is if that +9v connection on Com for the motor would somehow feed back through the inputs to the servo or Arduino if I do that... but... I don't think it would. I think there's diodes in there to prevent that. I would like confirmation though.
The reason I'm going to all the trouble to design for both a stepper motor and a servo btw, is because at this time I don't know which I'll need in my final design. Either one could potentially perform the task I need, depending on how I engineer the mechanical connections.