Digital input maintains at 5V

[Shazlan]

Hi all,

I have experience a scenario where the digital input channel on my DAQ card is giving 5V when I measure between the channel and ground. As a result, I was not able to read the digital signal. This happned in the past, a few months ago and my work around it is to change to another channel. This time, I'm experiencing the same using my FlexRIO + NI 1483 module. There are four DIO channels and I've configured them so that 2 channels are input and 2 channels are output. Initially, everything worked fine but somehow, last two days, I was not able to read from the DI channels. Upon inspection, we found out that the DI channels (at NI 1483) are giving us 5V. 

I hope somebody could shed some light on why this happens.

Please advice.

Shazlan

[Henrik_Volkers · Accepted solution]

have a look at the spec, maybe a pull up resistor?

[PBP · Accepted solution]

Hi,

This may be due to inside pullup resistor. You may need to give GND to DI pin to get digital input.

Check TTL input connection.

[Shazlan]

Hi guys,

Thank you for your feedback. You are right, when we connect the port to a digital signal (originating from another instrument), the 5V is gone. What makes me wonder is why wasn't this behavior appear at the very beginning, when we first wire everything? It was initially 0V when nothing was connected. 

Shazlan