What should "Opto-com" connect to?

[phantomcow2]

I have three of these stepper drivers, which I have soldered up and all:
http://www.bright.net/~agarb/STMD/AVR_STMD.html

I ran them in test mode, and it worked. So I am pretty sure all is well.

I am now trying to get some motors to run. I have a logic input of 14v, which gets reduced to 5. It calls for 9-20v input. I have a motor input of 28v, this has a max of 48 I think.

So I have it so that my pin 2 if X step, pin 3 X dir. Pin 4 is y step, and pin 5 is y direction.
But theres also this connection, "opto-com". What is this supposed to connect to? I can't figure that out. Kcam is the only thing that seems to run on my laptop, so I have that setup. When I connect the opto-com to the ground pin (25) on my breakout board, I get no movement at all. For some reason, I connected opto-com to the same pin as step. Well, it works....in one direction. So I can get my motors to rotate one way only. Does anybody know how to rectify this?

[CJL5585]

When I connect the opto-com to the ground pin (25) on my breakout board, I get no movement at all. For some reason, I connected opto-com to the same pin as step. Well, it works....in one direction. So I can get my motors to rotate one way only. Does anybody know how to rectify this?
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Per the schematic Opto_com is NOT hardwired to the 5 Volt logic supply ground. This point is the (Cathode) or the ground end of the LED inside the optocoupler. The 5 Volt signal which comes from the parallel printer port to the breakout board goes to the (Anode) or positive side of the LED inside the optocoupler. So, when a positive 5 Volt signal is applied to the step or direction input pin the appropriate LED will illuminate internal to the optocoupler and create a signal path.

In this configuration the Opto_com connection requires a connection to the ground pin (25) on the breakout board.

In order for the system to work as designed, the software you are using must be set-up for the Outputs to be set to Active High. This means that a 5 VDC signal pulse is present with each step of the motor, and that when 5 Volts is present at the direction pin the motor steps in one direction, and when the direction pin sees 0 VDC the movement is in the opposite direction.

Looking at the schematic, I believe that you will have to have 5 VDC on the Enable pin in order to have an output. I did not see anything that would explain how you had movement with the Opto_com signal to the step pin. Under normal conditions the unit would not allow movement with the step pin pulled low and remaining low. (It could have allowed movement, however, if the direction pin was the one held low.)

EDIT:
If you can, verify that the output voltages from the parallel printer port are near 5 Volts DC when a logic 1 or "HIGH" output is sent. If you are using a laptop, some output the logic 1 levels at around 3 Volts DC which will not switch logic levels designed for 5 Volts DC.

Hope this helps.
Jerry