stepper driver help!

So I've designed a translater using basic 74 series ttl gates. I've designed both a half and full step translater. I finished soldering together the parts and i tested out the four outputs and the full step sequence was correct. However I hooked up the outputs to a ul2003 darlington array chip to the stepper motor and it would not move at all.... I probed the inputs and it looks like the translator output is greatly attenuated. is there a way to keep the origial signal without attenuating? could i just use a 7407 buffer between the driver and translator?

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The ULN2003 darlington array is made to sink current. It needs a power source. If you've got a unipolar stepper with 6 or 8 wires, your wiring could look like this (view in fixed font or M$ Notepad):

| | VCC VCC | + + | | | | ___ | ___ ___ | ___ | .-UUU-o-UUU-. .-UUU-o-UUU-. | | | | | | |2/7 ULN2003| |2/7 ULN2003| | O O O O | / \\ / \\ / \\ / \\ | (___) (___) (___) (___) | | | | | | | (created by AACircuit v1.28.5 beta 02/06/05

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It might help if you describe your stepper motor. Voltage, current requirement, how many wires (4, 6, 8).

Good luck Chris

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Can you put a number on "greatly attenuated"? A 74xx series TTL gate should be able to drive a ULN2003 with no problems (to a couple hundred mA output current anyhow). The input voltage will drop a bit, but probably still more than 2.5V. Are you pulling the supply down?

Best figure out what you are doing wrong first.

Best regards, Spehro Pefhany

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Spehro Pefhany

I have not looked at the scnematic of that driver, but... *If* it is nothing more than a number of darling transistors (as mentioned) and if the emitters go to ground, the bases will not go above (roughly) 1.3V - which is significantly less that an OC TTL output, hence the term "attenuated". Maybe that severe load over-stressed the TTL and so now cannot drive the bases enough to "saturate" the darlingtons?

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Robert Baer

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