How to generate a ttl pulse with a NI 9401

[Humada33]

Greetings All-

I have a camera that I intend to trigger when the voltage of a device reaches a certain limit.  I am using a 9127 USB chassis for measurements and a 9401 for the trigger output.  I have not had much luck actually I have not been able to generate an output signal at all. 

I am using Labview 8.5 but I was using signal express to see if I could generate the signal.  This seems to be a straightforward problem. Does any have any advice?

[Brandon_B]

Hello Whistler24,

You mentioned that you were using a 9127 USB chassis but I think you meant a 9172 cDAQ chassis with a 9401 module.  Also, you said that you would like to set a trigger once the voltage went above a certain level, so I am assuming that this is an analog input voltage that you are taking.  If so, what module are you using to take the input voltage?  The 9401 is a digital I/O module, so are you using this to trigger the camera?  Depending on what module you are using for the input voltage, we can determine whether it supports analog reference triggering, and if not, we can come up with a different method to implement your application.

Regards,

[Humada33]

Brandon,

Thank you for the reply.  You're correct in that I am using a 9172 cDAQ chassis with a 9401 module. I am measuring analog voltage with a 9219 module on 4 channels. When Channel 0 reads a certain voltage I would like to trigger the camera to begin recording.  The camera has a low value TTL input which is why I am using the 9401 module.

Chris

[Brandon_B]

Hello Whistler24,

I would suggest using a case structure to compare the value of AI0 on the 9219 to your specified voltage.  You can use a greater than or equal to comparator and wire this to the case structure.  This will result in two cases; the first is if it is not greater than or equal to your specified voltage you will just pass the wires through the case structure with no operations happening.  The second, is if it is greater than or equal to your specified value then you can use a DAQmx Write VI to write your TTL value from the 9401.  Please let me know if you have any further questions regarding this program implementations.

Have a nice day,