It depends on whether you want your default state to be logic high or low.
Use a pull up resistor. Wire one end of the resistor to the center pin of the BNC connector. Wire the other end to a 5V rail. This will come from an external power supply.
Use a pull down resistor. Wire one end of the resistor to the center pin of the BNC connector. Wire the other end to the ground on the BNC connector.
Let me know if you need clarification on this.
Actually, you don't need to use resistors at all. Your M-series device supports programmable power-up (default) states. See the following KB on how you can set the default sate of the Digital I/O lines on your device.
Thanks for that inbelievable quick reply 🙂
Though, I think I do need some kind of proper grounding because I'm experiencing some problems with my triggering. I'm using a counter to watch for a trigger on a line, and I notice it sometimes sees a trigger for no apparent reason. I suspected grounding issues?
I'll check the default state of the digital line tomorrow. There is a chance it is indeed not set to low. I'm indeed looking for a rising edge of a TTL pulse. I remember checking the trigger signal and it's a perfect 5V pulse if I remember right. I'll recheck all those things tomorrow at work and I'll report back.
Just to be sure: I only have to set the default state to 0 and connect the inner pin of the BNC connector to the particular line. I do not connect the outside of the BNC to anything...?
Thanks and 'till tomorrow.
I don't know exactly what you mean with:
Ideally you would find a BNC cable which would provide a perfect connection for you (with ground referencing).
The connection on the device that is generating the trigger is a BNC connector.
The device I'm triggering (as in controlling with my DAQ card) has also a BNC connector, but that is another story. I suspect I'd apply the same technique to both, so lets just stay with the problem above for now 🙂
No apologies necessary. I never explained it very well , so
... there is no BNC terminal on the USB-6251 . Or it must be very well disguised 🙂
I guess I'll connect the center pin of my BNC connector to the line I'm using to watch for a trigger. The outer shell to the Digital Ground. Correct me if that's not the way to go.