Can the supply for several inputs be connected together to monitor several contact closures? For example, pins 2, 4, 6 connected together and to the “common” terminals of three SPST switches and the NO terminals connected to pins 1, 2, 5 respectively. This would permit the use of four conductors instead of six.
That is a good question - The specification show this is non-isolated, which would mean all the supply pins should be connected internally. However, this is usually shown on the wiring diagram and it doesn’t show that, so I am not 100% certain, only 99% certain.
If you have the module, you could check it with a voltmeter to see if they are isolated or not - I don’t have one with me at the moment to check myself.
To Opto22: the wiring diagram for the digital input modules really could use an update to clarify this - these ones don’t even have pin numbers (on the GRV-IDCSW-12) on them and it would be nice if it showed the internally connected pins like the datasheets for other modules. Opto22 - 2236 groov 10–30 VDC Input Modules Data Sheet
I perhaps should have posted that I have reached out to the hardware guy that designed this thing and am waiting to hear back… Its a great question, one I have not thought of, but makes sense.
I’m really slammed on a big project and am out of the office delivering it next week, so don’t have a sec to find a module and run the test… Lets wait and see what the hardware engineer says.
Ok, we have an answer @James_R_Talich
Short answer: No. You cant.
Long answer. Each and every output is current limited, when you join them up as you propose, you might get some circulating current is not intended, you also might end up with more current flowing over one or more of the switch lines than you expect.
On the input side, you might also have some issues if one of your ‘group’ is the only closed switch, it might be sinking more current than it was designed to sense / manage.
Bottom line, each output and input is designed to be an isolated matched pair.
Interesting - if he used an independent DC supply would he be okay?
No. The module has the DC-DC converters that are current limited for each channel.
As soon as you hooked up the external DC supply, you would have the ground loop problem I described?
I understood what you wrote to be an issue with the independent channel DC-DC supplies causing unintended/unbalanced current between channels. An external supply wouldn’t have that issue.
I mean, sure, drop using the switch module, use a DC supply and a DC input module.
Problem solved.
You can group what you need over what ever wire count.
It would be on you to ensure any shorts are current controlled and the whole thing fused.