Parallel isolation board for CNC

[Sparkey_500]

I would like to show off a project i've been working on, it's a inline plug in isolation board for the parallel interface.

The circuit consists of optoisolators with selectable inverting or non-inverting outputs via solder bridges and component placement.

So far i've got it working on direct 5v inputs, but sadly it doesn't seem to want to work on the parallel port. I think the problem has to do with the resistor values and the maximum current supply of the parallel port.

Sadly I known just enough electronics to build stuff but not enough to work out whats causing the issue.

[Sparkey_500]

Here is a picture of the board, I got it made by breadboardkiller

[awallin]

especially on laptops the parallel port voltages can vary a lot - try to measure it with an oscilloscope. if you think the high-state is 5V it may actually be 3V or 2.7V or something like that. also depending on the port it may require a pull-up resistor.

[dadler]

In what way does it not work on the parallel port?

Exactly which PC817 opto are you using?

[Sparkey_500]

I'm using a standard atx motherboard which has 4.35v (not 5v  ) on the parallel bus.
I changed the settings in the software to active high (from active low) and i'm getting some signals out the other side.
I also noticed that the X axis data gets through but the Y axis data doesn't, So i probed the Y axis signal and it's half the voltage of the X Axis.

My CNC works fine without the isolator board in place, so i guess the computer and CNC side isn't the problem.



I used optoisolators since they are 10c each and are simple to use. and my system only runs at 33KHz