7i77 input protection

Hello

So I'm having some annoying problems where my 5i25 and 7i77 looses contact with each other and I have to restart linuxcnc.
It usually happens during a toolchange (relays and voltage spikes?) but also when cutting and sometimes even when the machine stands idle with the machine disabled.
And I've just bought an Emcoturn 340 slantbed lathe witch is going to be retrofitted with Linuxcnc using 5/6i25+7i77. But I was wondering if I need to build in some sort of input/output protection to get rid of this problem?

Something like:
Inputs
Machine sensor > optocoupler > 7i77
and outputs

7i77 > optocoupler > transistor > relay > machine actuator
or just
7i77 > TTL MOSFET > machine actuator

Thoughts?

The basic problem is there is likely a ground loop in your system that introduces enough high frequency ground current noise in the 7I77 --> 5I25 cable that it generates more than a 1.4V drop along the cable and disrupts serial communications. This is made worse by the fact that there is a bug in error handling in the firmware/linuxcnc in LinuxCNC 2.7.0 to 2.7.3 that causes some single errors to be fatal.


There have been two recent changes that address this issue:

1. In LinuxCNC 2.7.4, the sserial error handling has been fixed so that single errors are not fatal

2. The 5I25/6I25 SSerial firmware has been updated to have better noise immunity (better noise spike rejection)

As a first step, I would update to LinuxCNC 2.7.4 and update the 5I25 firmware (from the 5i25.zip file at mesa)

Note that isolation of the digital I/O will make no difference (its already isolated)

Thanks!

I updated the 5i25 bitfile and linuxcnc to 2.7.4, so far so good. I haven't used the machine yet it just stands idle while I tear the lathe to bits