Trouble generating digital output pulses

[edmiles55]

I am trying to create a multiplexing setup to measure an array of SET's but cant seem to manipulate the digital outputs to cycle through the channels on the multiplexer. I am using a 16 channel multiplexer which requires five timing signals to cycle though all the channels. The output pulse allows for two signals as does the analog output. Using the digital channels would be best but I cant generate the signal I need. I am connected to the DIO channels in the break out box and have the express DAQ VI using the corrisponding port/line channels for output. Sampling is on demand. Help generating these digital signals would be great.

[Ed W]

Hi edmiles55,

Thanks for your post!

Use a counter signal to generate the clock signal of your fastest output.  Write the following patterns to your digital output lines:

line1 - 01

line2 - 0011

line3 - 00001111

line4 - 0000000011111111

line5 - 00000000000000001111111111111111

This pattern will cycle through all of the possible configurations for your mux.  There is an example that already does this exact same thing, but in continuous rather than finite mode.

In the Example Finder in LabVIEW, look for Hardware Input and Output >> DAQmx >> Digital Generation >> Cont Write Dig Port-Ext Clk.vi

I hope this helps!

Ed W.

Applications Engineer

National Instruments

[edmiles55]

I understand the signal I need to use to cycle through the mux. My problem is getting the DAQ to send that signal through to the breakout box.  The problems I am having are
1. How do the port channels corrispond to the Digital I/O channels
2. All digital channels see only a 5V signal.
I am trying to keep the VI limited to the express VI's so that it is easier other in the lab to interpret and change, but even the examples that you pointed out wont run. I recieve an error message saying that I cant select sample clock. I am only allowed to select on demand. If you have some ideas as to what I am doing wrong it would help greatly.

[Ed W]

Hi edmiles55,

The port is a group of I/O channels.  You can find out which ports correspond to which digital lines in the pinout of your device.  This can be found in Measurement & Automation Explorer (MAX) by right-clicking on your device and selecting Device Pinout.

Have you tried testing your output lines in MAX.  There are test panels that you can use in MAX to test the digital outputs.  You can change the value of the outputs here and test whether the +5V signal changes to 0V.

Let me know the results of these tests and how that example program worked for your needs.  From your description, it sounds very close to what you’re looking for.

Ed W.

Applications Engineer

National Instruments