Trouble receiving inputs over parallel port

Currently, If I put a probe between those pins (sensor input and ground) and close the switch I'm reading a drop from 24V to 0V across the screw terminals. Doesn't seem to trigger the optos though. I'm reading no change on their output and if I probe the pins on the bobs paraport out I'm just getting a constant 4.7V out of pins 11,12, 13... etc

I'll add resistors as described and see if that solves my problem.

I tried a range of resistors and no joy.

The input is already being pulled to 0V on the machine side of the optos when an input is triggered.

I don't see any change on the computer side of the optos. Both the collector and emitter pins read 0v when referenced to ground. The paraport pins on the bob that connect the input signals to the computer are always reading 4.7V. They should be being pulled low when the switch is triggered I'd imagine but no.

Starting to think the optocouplers are just borked. Any other clues about the probelm given the symptoms?

Dang! Well I just tried this. Looks like my on board parallel port card and the additional one I've installed are both goosed.

Shorting the input pins to ground didn't result in a signal being received when watching the pins in hal.

Are there any other settings in software, bios or elsewhere that I can check before resorting to new hardware?

Also, it seems unlikely that both these ports were defective, with the same problem of working outputs and broken inputs. I'm guessing I've caused the fault if it is a hardware problem. What could I have done to fry the inputs? So far as I can tell the bob just sinks them to ground when a switch is triggered it doesn't have any way to cause damage to the PC hardware.

Before you give up on your existing ports. Try shorting one of the output pins to one of the inputs. Then open the parallel port tester in Linuxcnc and press the button to trigger the output you shorted to and see if the input changes. (Assuming you've defined the port address correctly. )

Also, it seems unlikely that both these ports were defective, with the same problem of working outputs and broken inputs. I'm guessing I've caused the fault if it is a hardware problem. What could I have done to fry the inputs? So far as I can tell the bob just sinks them to ground when a switch is triggered it doesn't have any way to cause damage to the PC hardware.

Just throwing this in. The PP cable is a 25pin cable with all 25 pins connected have you verified that.?

If you re-read my original post, sorry I know it was information dense, I mentioned that I already tried this:

"I tried "piping" this signal back in to one of the input pins to see if it would change it's state when I triggered the output but all pins remain active."

Was just clutching at straws when I tried it but it seemed like a logical enough thing. No change is state of the input pins in paraport tester though.Good to know it's actually a viable diagnostic technique though.

I'm pretty certain I've defined the ports correctly I wouldn't be getting step and dir signals to my motors otherwise, right?

Clive wrote:

Also, it seems unlikely that both these ports were defective, with the same problem of working outputs and broken inputs. I'm guessing I've caused the fault if it is a hardware problem. What could I have done to fry the inputs? So far as I can tell the bob just sinks them to ground when a switch is triggered it doesn't have any way to cause damage to the PC hardware.

Just throwing this in. The PP cable is a 25pin cable with all 25 pins connected have you verified that.?

Now that's something I've not checked. Just assumed that the cable would be wired 1-1 2-2 etc and all pins would be connected. Are there cables out there that don't have all 25 pins connected to their corresponding pins on the other side of the cable?

F4br1c4t3D wrote:

Clive wrote:

Just throwing this in. The PP cable is a 25pin cable with all 25 pins connected have you verified that.?

Are there cables out there that don't have all 25 pins connected to their corresponding pins on the other side of the cable?

Yes there are.