Digital I/O Channels on myDAQ

[jay.shah]

Hi,

I have a my DAQ device on which I am trying to send some signals and testing them out through a multimeter. I am trying to send a digital high command to one of the digital output ports, but on the multimeter I am reading 0V, instead of 5V. I tried sending the command using the test panels of the myDAQ device, and also using a python script. The script is as follows:

import nidaqmx

task1 = nidaqmx.Task()
task1.do_channels.add_do_chan('myDAQ1/port0/line0')
task1.start()
task1.write(True)
task1.stop()
task1.close()

The code runs successfully without any error.

On a video tutorial online, I saw that the guy was reading the values directly out of the digital output pins of the USB device without any external pull up resistors. But I suspect myDAQ device might require external pull-up resistors. Some clarification on this might help me a lot. Thanks.

[Apex_Waves]

Hi there, 

You want to make sure you have the multimeter leads connected properly. The HI (red) should be connected to the left red jack on the multimeter. The right is for measuring current. Make sure you have a good connection to port 0 of the DIO and DGRND.

You will also want to make sure that you are on the first setting in NI ELVISmx for DC voltage. You can test the multimeter by measuring the last port labeled 5V to DGND- it should always read 5V. However, the voltage from the digital out will only be 3.3V when switched to the HI position.

The code works correctly.

Hope this helps!

[jay.shah]

Hi @Apex_Waves,

Thanks for your response. The multimeter leads were measuring the voltage as I was measuring voltages at other places too. I am able to read a voltage when I used a pull-up resistor. I did not know that these pins did not have an internal pull-up resistor. Nevertheless, it is working now.