How to use GPS to trigger analog input acquisition with cFP?

[TheNet]

The issue is pretty much explained in the subject line.
How can I use the PPS signal coming out of the GPS in order to trigger
acquisition of an analog input (cFP-AI-110)?
I'm quite stuck here, I would appreciate your help...
Thanks!

The Net

[Mike S. @NI]

FieldPoint modules do not currently support hardware triggering. You will have to poll for the signal in your program and read the FP module when the trigger occurs. To minimize this delay, you could run an embedded LabVIEW Real-Time application on your cFP-20xx module.

Regards,
Michael Shasteen
Applications Engineering
National Instruments
www.ni.com/ask
1-866-ASK-MY-NI

[TheNet]

> FieldPoint modules do not currently support hardware triggering. You
> will have to poll for the signal in your program and read the FP
> module when the trigger occurs.

That would be a great solution. Let me see if I get this right. I can
read the analog PPS (Pulse Per Second) signal from the GPS through the
local cFP com port and use it to master the analog input module
acquisition. Now the issue is how to implement it.
My first question is: how to poll such a PPS value continously, that
is not sampling it but waiting for the trigger level to arrive?
Then, once I do that, how to use the trigger signal to get a single
sample from the input channels?

Thanks for your reply,
Nicola

[Mike S. @NI]

I did not realize that your GPS device sent signals through RS-232; many of the ones I have seen use a TTL signal. Since it is serial, you can use the serial (non-VISA) VIs in a while loop. You would of course need to ignore errors when there is no data received. When data is received, you could use a case structure to compare it to the expected results and determine whether or not to run FP Read.vi to read the AI channel.

[TheNet]

> I did not realize that your GPS device sent signals through RS-232;
> many of the ones I have seen use a TTL signal.

Mine is a Garmin GPS25-HVS, which has "two birectional RS-232 serial data
ports". I don't think it has TTL signal/logic.

> Since it is serial,
> you can use the serial (non-VISA) VIs in a while loop. You would of
> course need to ignore errors when there is no data received. When
> data is received, you could use a case structure to compare it to the
> expected results and determine whether or not to run FP Read.vi to
> read the AI channel.

When you say "when data are received", you're talking about the PPS data or
the GPS position and time signal?
Note that I'm both interested in the PPS and location signal coming fro
m the
GPS. Location signal would provide positioning information, PPS would
trigger AI acquisition.
But since the flow along different wires, how can I input both of them into
the cFP com port if I only have one RX wire on it? Should I use two
different com ports (I have cFP-2020)?

Sorry for the bothering questions, you can certainly tell I'm totally new to
cFP and labview in general...

Regards,
Nicola

[Mike S. @NI]

You should use both com ports on your 2020. You can monitor PPS to trigger AI and also read location to use however you wish.

[TheNet]

> You should use both com ports on your 2020. You can monitor PPS to
> trigger AI and also read location to use however you wish.

Cool! But if I do that, wouldn't I consider the PPS signal as a binary
signal? It is not clear how to keep the output of the com port analog and
how to get the trigger signal (which would be on the raising edge of the PPS
square wave) for the analog acquisition...
I don't want to bother, I would be more than happy if you could point me to
some online resources that can help me...

Regards,
Nicola