Re : Re: Re : How do I enable DIO with a high in Test Panel?

[Microtweet]

Using Digital I/O in Measurement Explorer Test Panel

This is going to be very elementary for most of you, but I am having a heck of a time. All I want to do is set DIO Input line #0 to low and activate it with a 5V high. I am using a 6062E DAQMx PCMCIA card. I've tried both BNC2110 and BNC2120 input devices. When I set the DIO lines as inputs in test panel, I cannot reset the lines to zero, and therefore applying a 5V high has no effect since they are all already high. I read about a pulldown resistor and high impedance power-on states, but it doesn't seem to help me. I cannot change the state of any digital line by applying a high. Thanks!

[JB]

What happen if you connect the DI to the GND ? The state should change to the low level.

[Microtweet]

Of course it goes low when I apply a digital ground. I want to bring an external line in from say a PLC. And I want to see the state change in Test Panel when that line goes high.

[JB]

I recommend to use this interface to isolate the PLC from the expensive DAQ board. Adapt the value of R6 if the output level of the PLC is not 24V (eg 330R for 5V).



PLC high (24V) --> DI high
PLC low (0V) --> DI low

Am I missing something ?


Message Edité par JB le 03-28-2008 06:00 PM

[Microtweet]

I appreciate the opto-isolator interface, but still doesn't answer my question. It's much simpler than that - I think. I want to see the light come on in Measurement Explorer's Test Panel DIO tab when I apply a 5V signal to any one of the eight digital IO channels on the BNC 2110 or BNC 2120. By default, the DIO lines are all "high" in Test Panel, so you have to apply a low to see a response. Do I need to have some additional hardware configuration that allows me to pull all of the DIO inputs low - so that all of the lights go out, that will allow the DIO Input channel lights to light or activate when I apply +5V to any of digital input lines on the BNC 2110 or BNC 2120? I don't know how to explain it any simpler than this.

[Dennis_Knutson]

The DIO is correctly reporting when an input is at +5V and correctly reporting when an input is at gnd. Is your question about how to detect when nothing is connected?

[Microtweet]

I appreciate all of the responses, but I don't know how to make the question any plainer. With nothing connected to the DIO's, the status of all DIO inputs is high in the Measurement Explorer Test Panel. When you connect a 5V signal to the Digital input, obviously nothing happens, since it is already high. If I apply a digital ground to the Digital input, the level goes low. How do I get the test panel DIO inputs to read "low" when nothing is connected, and high when +5V is applied? I guess it's really not an elemenatary question for all of you experts out there after all.

[AnalogKid2DigitalMan]

Microtweet:

You had the answer in your own original post- pulldown resistors.

[Dennis_Knutson]

Well, in my opinion, you kept asking the wrong question since it was correctly detecting the presence of +5V and gnd. This is the very first time you said you have an issue where nothing is connected.

The card has an internal pullup so seeing a logic 1 when nothing is connected is expected behavior. Some of NI's cards have the ability to change from a pullup to a pulldown. I don't know if your board has that capablity. If it doesn't, you would need to provide an external pulldown.

[Microtweet]

In the original question, it was clearly stated that by default, the inputs were high, and then applying 5V obviously had no effect. If it injures your pride that I suggested you misunderstood the question, then I apologize; you were right, I was wrong. The manual lists values and a diagram for using pull-up resistors, but I don't see how that would help, since I need to pull down the input, until a 5V signal is actually applied (interpreted as a voltage potential of +5V DC with respect to ground on an actual wire inserted into the DIO connector ) - and I obviously haven't figured out how to do that yet.