PCI-6232 DAQ - DIO Question

[SGC]

Hi,

     I am using the DIO lines on a 6232 DAQ card to drive a ULN2003.  I have 5V powering VCC on the DAQ and the DIO port GND connected to the circuit GND.  With the DIO output line connected to nothing, when I toggle the DIO line high I see 5V as expected.  However when I tie the DIO line to the ULN2003 Input the voltage drops to 3.8V and VCC to the DAQ is still at 5V.  The current draw is only 2mA and I tried a simple resistor load and I get the same voltage drop.  Has anyone expierenced this before and know what I may be doing wrong?  Thanks

Scott 

[tnek]

Hi Scott,

Does this voltage drop change when you increase or decrease the load? In addition is there enough current going to the Vcc pin? One reason for this behavior is the fact that this board uses Darlington drivers for the digital output. There will be a voltage drop associated with this. Here is an article which documents similar behavior. The numbers may be different due to the actual hardware used.

Regards,

Kent

Applications Engineer