Help with I/O Ports

staticattic

I have an NI-3100 and am trying to use the I/O ports to verify if an A/B switch is in position A or B. When the switch is in A, the status pin puts out 0VDC with respect to ground. When the switch is in the B position, the status pin puts out 5VDC with respect to ground. I have taken the status pin wire and ran it to I/O 1. I took the ground wire and ran that to the ground I/O pin. The I/O never does anything. I have a multimeter and can verify the voltage is there. I have gone through the AMX manuals and on paper, everything is connected properly. What am I doing wrong? Thanks.

ericmedley

There are a couple of things in this situation but I'll skip to the end.

I've found that (in general) it is a good practice to keep such things separate when possible. If it were me, I'd put a relay on the output of the switch your speaking of and then use the contact closure of the relay to connect to the I/O of the AMX master.

This does a couple things:

1) it physically separates the master from the switch circuit. Not that anything might happen but I've personally been bit in the rear end by stuff like this when it fails or whatnot. I just don't like the idea of sending voltage from another device into my boxes. (albiet even low voltage...)

2) it simplifies your use of the I/O port. I've found that the I/O ports can be somewhat fussy about sensing voltages. It seems simple enough but I've found that input/output impedences can get screwy between the AMX and whatever else and it results in strange behavior. However, if the voltage is used to charge an electromagnet in a relay it seems to work more reliably.

Now, it does introduce another component and the possibility of failure there too. But, I've found this to be a non-issue. Use a high quaility relay and you should be fine.

That's my 2 cents...
e

staticattic

Thanks. I am a fan of relays myself. I always put relays in my car stereo system between the power wire that runs form the head unit back to the amp that powers on the amp when the head unit powers on. I do it for the same reason as what you said. It might be overkill, but I sleep better at night knowing it is there.
I was trying to make this project work with what I was given. I guess I need to take a trip to Radio Shack and pick up a few relays. Thanks again.

ericmedley

staticattic wrote: »

I guess I need to take a trip to Radio Shack and pick up a few relays. Thanks again.

Hey, I'm always looking for an excuse to hit 'The Shack' whenever possible.

DHawthorne

So you understand why what you tried didn't work, IO ports have a nominal voltage present in the normal state (5V), and are triggered "on" by a voltage drop ... usually by completing a circuit to ground. 0-1.5V registers as a PUSH, and 3.5-5V as a release. When used as an output, they complete a circuit to ground when turned "on." But what you did was to provide 5V to attempt to trigger it, which resulted in exactly nothing, since the port was already at that state. They can be programmed to work as you hooked it up by reversing the logic with the SEND_COMMAND "SET INPUT # HIGH," with # being the port number. If you do that, it disables it's ability to be used as an output though.

But Eric's point is a very good one, and what I consider best practice. By directly connecting and outside voltage, you run the risk of blowing the TTL that drives the IO port. In my experience, that can mean anything from that particular IO not working to none of them working ... and losing the 12V output as well. In extreme cases, you can blow the whole controller chassis (happened to me once, but that was enough). Isolating your input with a relay is highly recommended. The one exception I would make to that is when using an AMX device like the VSS2 or PCS, which were specifically designed for that purpose.

TurnipTruck

ericmedley wrote: »

Hey, I'm always looking for an excuse to hit 'The Shack' whenever possible.

Are they still selling parts? I thought is was all cell phones and satellite systems these days.

Check out: www.radioshackcatalogs.com for some nostalgia.

ericmedley

There's one store nearby us that we call The Shack "Classic" that still does. They keep warning us that they're going the way of cell phones, radio controlled toys and weather radios, but they haven't pulled the switch yet. I know that day is coming, however.

We also still have a good old fashioned electronics parts store complete with shirtsleves, hoorned rimmed glasses and pocket protectors. That too is going the way of the Wooly Mammoth. Ha! remember when those were roaming around free on the plains! I do. Those were the days those were the days...... zzzzzzzzzzzzzzzz uprphmph ah did is doze off?

TurnipTruck

One of my first jobs was in a Radio Shack repair center fixing consumer electronics. I repaired audio amplifiers, TVs and VCRs. I don't think anyone fixes this stuff anymore.