Stepper motor

Forum 2005-2010 (read only) General Frequently-Asked Questions
1

I found this tutorial on a stepper motor:

I see that it says that a ULN2003A driver chip is needed. For testing, however, as I dont have the chip on hand, could I do the following?:

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The diagram above, from another webpage, shows the motor being run with some transistors that run an external current into the motor. Ignoring everything above the transistors in this diagram, I wanted to use the arduino board as the control circuit to power the transistors like switches and connect to the 3.3v out pin from the board to power the motor.

Will this burn the arduino board up?

If this isn't clear enough, let me know and I can physically draw out a diagram of what I'm thinking.

Thanks,

Y-aji

2

Ignoring everything above the transistors in this diagram

Yes you have to as it is just rubbish. All it is is a threshold detector from a pot that turns all the coils on at once.

The only thing in controlling the FETs from an arduino is that I would put a series resistor of 33R or so to protect the arduino's outputs from excessive inrush current of the FET.

Have a look at this:-
http://www.thebox.myzen.co.uk/Workshop/Motors_3.html

3

Cool! That pretty much cleared it up. The reading material really helped. It took me a bit to realize the author was getting his sequence numbers from binary.. When i saw those numbers I scratched my head for a minute as they seem so random at first sight: 3 6 12 9

Now that I realized it was a reference to binary, I put together that he meant it like this:

8 4 2 1

0 0 1 1
0 1 1 0
1 1 0 0
1 0 0 1

Seeing as my stepper motor only has 4 contacts total, I guess I have to do this with 3, right?

4 2 1

0 1 1 = 3
1 1 0 = 6
1 0 1 = 5

It only has 4 contacts, so I'm assuming that one lead has to be used as a power source and i only have 3 left, or can i ground it on something else?

Thanks again!

4

OHHHHH! (read further).. So the whole point of using that ULN2003A driver chip, instead of 3-6 transistors is to reduce the number of pinouts that you are using (and cost) from as many as 6 in some motors down to just 2, one to say which way and the other pin to say when to move forward and how quickly.

I love when things suddenly click like that..

Thanks again for the read.

5

You will not be able to drive those MOSFETs directly with an Arduino output pin. They require 10vdc to saturate fully on and the Arduino can only output 5vdc. You require either logic level MOSFETs or you will have to use driver transistors to switch a higher voltage needed by the MOSFETS.

Lefty

6

I use FET IRFZ34N without any drivers (only gate's resistor about 100 Ohm) to run 60W 24VDC motor from an Arduino output.
Wal

7

Don't forget to put a diode (not less than 2A strong, may be more) in reverce polarity parallel to each coil. To protect transistors.