stepper motor circuit

willy1067

Just got my first Basic Stamp homework board, and put this circuit together from page 264 and other circuits online,· my question is, Will it work?·· I am new at this and would welcome the help.

Can the power supply be 7.5 volts 1 amp, or do this circuit requires more power?

Is this Circuit OK?

T Chap

Why two resistors to the gate? One is sufficient. This circit needs rethinking after looking at it and you could do it much easier, is that a Parallax schematic?

First understand the fundamentals of what needs to happen to spin a unipolar stepper. There are 4 coils. The coils need to be turned on in sequence by the Stamp. The center of each coil goes to +V, that means you have to SWITCH the GND on and off to make it run. This switching is done with the transistor, a diode is used across the coil to prevent the voiltage being "generated" from flowing back to the transistor. There are 9 million stepper circuits on google, maybe you have seen them. Picture in your mind the 4 coils that permanently have the +V to them, and you need to shunt to GND the side left open on each coil. The transistor acts like a relay when a signal is put to it's gate. The gate is just that, a way to allow the current to flow.

Here is a much simpler way to go, with much less parts. There are newer versions of the transistor array, try a ULN2803 which contains 8 darlington transistors and built in diodes. This is just a sample schematic, the lines on pin 2 and 3 do not need to be reveresed on the Stamp.



http://www.doc.ic.ac.uk/~ih/doc/stepper/control2/gif/connect4.gif

Hereis another variation:

http://hades.mech.northwestern.edu/wiki/index.php/Image:Unipolar_stepper_circuit_schematic.png

Post Edited (originator) : 3/10/2007 6:03:19 AM GMT

willy1067

The schematic is from "What is a microcontroller" page 264, there it used 2 resistors at a lower value, but after·chatting from someone here; he sujested increasing the value.· Maybe I missed understood, and he was just·telling me·to add the two values into one?··



Will the ULN2003 be able to handle 5.1 volts at 1 amp?·· I check the URL address you gave me and it saids, that the ULN2003 and 2803 can handle up to 500ma.· that's why I was making this circuit with Radio Shack Mosfet that can handle up to 3 amps.



Post Edited (willy1067) : 3/10/2007 6:01:12 AM GMT

T Chap

I think the 2003 will handle sinking .5 amps, the 2803 may handle .6 if I remember correctly. The volts are not what is going to blow stuff up, it's the current. Many stepper systems have a stepper that is rated at 5volts 2 amps, but they are driven at 24-26 volts easily by doing whats called current limiting" to maintain the 2 amps, which it may be too early for you to think about. Just hook what you have now, deoending on the type of transistor(or mosfet) you decide on, that will affect what the value of the gate resistor is. Honestly, I have no idea how to calculate that stuff. When learning motor, buy extra mosfets!

Here is a suggestion only, the more fundamentals you can get the better. Take the stepper motor, run 5 volts to the center of the coil. Then take one of the other wires (probably 4 wires) and touch one of them to GND. See if you can figure out the sequence to manual get the motor to move in a direction, then, find out how to reverse it. I forget, but with unipolat you may be able to keep it going with only one wire, some parts of the "sequence" may require 2 wires at a time though, find a unipolar single step sequence chart and note what combinations are ON to move it one step. This will help you "see" what is going on.

Personally, I would hook up the motor with one of the schematics I linked, and try it out. Then again, I have blown up a whole lot of stuff. Keep checking the transistors when you first power up a new circuit, they will get very hot early on if there is a problem. Keep one hand on the power just in case.

Post Edited (originator) : 3/10/2007 6:16:57 AM GMT

Chris Savage

This is a duplicate thread, please post only in the original at the following link.

http://forums.parallax.com/showthread.php?p=637017

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Chris Savage
Parallax Tech Support