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I am using an Easydriver v4 to drive a bipolar stepper motor. The Easydriver works fine, if I wire it up and manually toggle the step pin to 5V/GND it steps as intended.

Now I connected both the step and the dir pins to my Arduino. The problem is that apparently the Easydriver pulls 70mA through the stepper pin (which exceeds the maximum current of the Arduino) in turn making the voltage drop to about 2V instead of 5V. The consequence is that the motor does not step when controlled by the Arduino.

I wired everything up just like in the image below:

Wiring

I both tried powering the Arduino through USB and from the 5V current that is conveniently supplied by the Easydriver.

Any ideas what I might be doing wrong?

Edit: I just discovered that the behaviour is the same whether or not the EasyDriver is powered or not. Do not know if that makes any difference ...

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    \$\begingroup\$ That doesn't seem right - the board schematic shows direct and only connection to A3967 input pin, and the datasheet thereof specifies 20 micro amps maximum draw. Is this true of both pins? Do you have SJ2 closed misconfiguring the board for 3.3v in? How exactly did you measure the current draw? \$\endgroup\$ – Chris Stratton Oct 22 '14 at 18:09
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    \$\begingroup\$ Are you absolutely sure you don't have the ground connection accidentally tied to the 5V pin of the arduino, rather then the ground connection? \$\endgroup\$ – Connor Wolf Oct 22 '14 at 18:16
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    \$\begingroup\$ If only one pin is doing it, it suggests it might be solder bridged to something else (step is adjacent to a motor output, but dir is not), or it could have suffered damage from electrostatic discharge (or previous mis-connection). \$\endgroup\$ – Chris Stratton Oct 22 '14 at 18:21
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    \$\begingroup\$ Ok, so it's not that. What current draw do you see if you connect the pin to VCC (which apparently works), through the multi-meter? \$\endgroup\$ – Connor Wolf Oct 22 '14 at 18:21
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    \$\begingroup\$ Careful - the inputs can reasonably be connected to the logic supply, but not to the motor supply. \$\endgroup\$ – Chris Stratton Oct 22 '14 at 18:46
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I just contacted the creator of the EasyDriver via e-mail and he answered me that he has heard about these symptoms and that - at least in some cases - it could be traced back to an over-voltage on this pin (likely an ESD).

The solution he advises is to either replace the IC (requires soldering skills) or to just get new EasyDrivers.

This is kind of sad, because the units still seem to work if supplied with a high enough current through the "step" pin. A possible solution might be to use transistors to switch current from the Arduino's +5V pin (or the EasyDriver's 5V output) to the step pin.

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