How did you wire your Mesa 7i37 Limit Switches??

[torinwalker]

Hey guys,

After weeks and weeks of research, accumulating parts, building an enclosure, and wiring the whole mess together, I finally tuned and moved my z-axis up and down at 225 ipm! It's a beautiful thing! (I still have a following error when I let go of the mouse, but that's a different story.)

Anyway, I'm having a helluva time getting my Mesa 7i37 IO card to detect a change in the limit switches (or any circuit closure for that matter), and I would like to know how you wired your 7i37 to cause your limit switches to work.

I know the card is working because when I apply a +5V signal, for example from my amplifiers' fault lines, I get the reading as one would expect.

I even went so far as to try to force the GPIO as an input using the is_output false directive with no change.

Anyway, what I'm trying to do is wire the switches in a normally closed (NC) configuration so that they ground (pull the signal low) until tripped. When the switch is tripped at its limit, the circuit will open allowing the 5i20's weak pullup to raise the signal to +5V, in turn causing EMC to detect the limit.

The really odd part here is that when I close the switch, nothing happens. I've confimed it several times with a DMM and have even installed a jumper between the two pins with no change in the outcome.

I'm sure I'm doing something wrong, and I'll figure it out eventually, but I would really like to confirm this one thing:

--> If I put a wire, or close a switch across the IBIT0+ and IBIT0- pins, should it not pull the signal low??

Thanks, everyone... anyone...


Torin...

[unterhaus]

I haven't done this yet, I'm about to get started on my mill again so I'll be able to help you in a week or so. You would think that shorting the two pins would be enough. However, it looks to me that you have to supply your own voltage. It would make no sense to supply an internal voltage to an isolated input. As I read the manual, the resistor is in series with the optoisolator to provide over-current protection, not as a pull-up.

Now that I read your post again, this is your problem. You need to supply a voltage (through a resistor to protect the power supply) to pull the optoisolator high.

[torinwalker]

I originally got the idea from a variety of posts that shorting these pins would pull the signal low. You are correct. I should have read the manual a little more closely. Peter Wallace from Mesa set me straight this morning.

I am now wiring 5V to the common of all switches and returning each NO output through a separate line to the IBITx+ input, then routing the IBITx- back to the ground pin from whence the 5V+ signal came. I'll then then use the in_not value from the mesa card to feed to each limit/home switch.

Hopefully, I'll have the limits wired by this evening, then I'll continue tuning PID and servo loops throughout the week. By the weekend, it's homing time.