Issue with Setting and Reading Digital I/O Pin on MCC USB-2408-2AO DAQ Device

[Mahendra Gutti]

Hello Everyone,

I am currently using the MCC USB-2408-2AO DAQ device in conjunction with an ECU. I've encountered an issue where setting a digital I/O pin to '0' results in the pin reading back as '1'. We are performing this operation using a Python module we developed with the mcculw library.

Our specific use case involves attempting to wake up the ECU using the DIO_2 pin, which is connected to a relay controlling VBATT. Despite our efforts to set the pin to '0', it consistently reads back as '1'. Additionally, we have turned ON VBATT in Dasylab and tried reading the value using the Python module, but it reads '0'.

Has anyone experienced similar issues or have insights on what might be causing this discrepancy? Any suggestions or troubleshooting tips would be greatly appreciated.

Thank you!

 

 

Edited July 24 by Mahendra Gutti

[Fausto]

Hello @Mahendra Gutti.

The USB-2408-2AO is behaving as expected.  Unconnected digital inputs are pulled high by default to +5 V using internal 47 kΩ resistors through jumper J6 on the circuit board.  Each DIO channel is an open-drain, which, when used as an output, is capable of sinking up to 150 mA for direct drive applications. 

When you configure DIO0 as an input and DIO2 as an output, and wire the two terminals together, you allow the circuit to pass from the internal +5V pull-up to ground when DIO2 is set HI, resulting in a LO reading for DIO0.  However, if you set the DIO0 channel as an input and wire it to the +5V screw terminal, it will read HI.  If you then move the wire over to the DGND terminal, it will read LO.  Thus confirming the digital I/O terminals can detect the state of any TTL-level input. 

Regards,

Fausto

[Mahendra Gutti]

Hello Fausto,

Thank you for the detailed explanation. We will proceed with configuring the DAQ device as you suggested and verify.