Sticking Home/Limit Switches - Please help

andypugh wrote:

So, the voltages at the screw terminals behave correctly, but the values on the parallel port pins don't.
How curious.

You could try measuring the voltages on each side of the opto-couplers (input and output pairs)

Clive wrote:

I am away for a few days. But I take it you are using a correct type of PP cable as they are not always pin to pin. Try another one.

tommylight wrote:

That is a 5V BOB, so nowhere shout it have 9V.
Remove the step down converter from 12V to 5V, that might be the problem ( i can bet my pinky it is), some do the switching on the negative side so having both grounds together makes some trouble,
Get a USB cable, insert it on the motherboard and to the BOB, remove the step down converter, all should be good, although the optos might have gone the way of the DODO!

Todd wrote:

It seems to me like when you have more than a couple of the inputs active the voltage there is dropping below a critical level for them.

Would it be too much trouble for you to test the board with more than a 12v supply (closer to the 24v). (It might be that an additional external pull-up might be nessisary when using the minimal 12v supply.)

tommylight wrote:

Had 2 of them, they have finicky inputs and highly sensitive to interference, so i added some more pull up resistors and they are still working on plasma cutters, but i can not recall in any way or form it mentioned anything other than 5V anywhere, except on the relay output.
Then again, reading through a Chinese manual is like .......add your own comment here...... .
Comes to think of it, they do have a jumper for choosing the USB or terminal power. Did you check that?