Can I use a NI-USB 6343 as a grounded input to trigger an injector?

[Brown@KTR]

I know that I checked this problem as solved but I would like to reopen it if that's possible.  I have a ULN2003A chip now but I can't get the injector driver to fire the valve.  There must be a problem with my connection to ground or I don't have the circuit set up properly.  I've attached a schematic and a picture of my setup. 

I have double checked that I'm getting a clean TTL output signal from the USB-6343.  From my understanding of the ULN2003, when the TTL signal is high the circuit is completed from the output (of the corresponding pin) to the ground pin on the ULN2003.  Therefore, shouldn't the input trigger to the P&H driver be sent to the building ground (via the negative terminal of the battery) when the TTL signal is high?  Or should I bypass the battery and connect the GND (pin 😎 of the ULN2003 directly to the building ground? 

I come from a math/mehcanical engineering background and I don't have much experience with electrical applications.  I'm learning as I go so I appreciate any help I get.

Thanks,

Mike

[johnsold]

Mike,

The building ground is not particularly important in this situation.  What is important is the the digital ground (D GND) of the USB-6343 needs to be connected to the battery negative and the ground of the ULN2003.

Lynn

[Brown@KTR]

That makes way more sense when I look at it now.

Thank you very much.  Everything is now working as it should be.

Cheers,

Mike