External trigger based data acqusition using USRP N200

[Rydaholic]

I want to acquire a analog video signal based on external trigger which is  a digital signal.

Digital trigger parameter:

Pulse Width= 1 uS

Pulse Duration= 1.6 mS

Using USRP example EX Rx Continuous Async, I have acquired the signal continuously but I want to acquire the specified no. of samples on every positive edge of the trigger i.e for 1uS only. I have no idea where to input the external trigger signal in USRP, read somewhere that PPS In can do the job but not sure and dont know how to do that. If any one have customized VI for this purpose please share or atleast guide me to how to do that.

[Jorr-El]

Hi Rydaholic,

Just a couple of clarifying questions,

What version of LabVIEW are you using? If you are not using LabVIEW, what software are you using to interface with your N200 USRP?

What daughterboards are you using with your N200?

If you're not using NI Drivers to interface with your USRP (niUSRP) you may have better luck by looking in the Ettus Stack Exchange for USRP or by emailing Ettus directly for support.

[Rydaholic]

Thanks for the reply.

Labview 2012  and  niUSRP Driver 1.2

USRP firmware is not updated to the latest version that's why stucking to the older versions of Labview and USRP Driver.

LFRX  LFTX.

[Jorr-El]

Hi Rydaholic,

Are you hoping to access the FPGA or just program the USRP using the API? If you're looking to just use the USRP API, I have a couple LabVIEW examples that may be of help to you (see attached).

These examples both use PPS IN on the USRP to read external digital triggers and start acquisition or generation after the digital trigger is received.

[Rydaholic]

Hi Jorr-El,

I have read somewhere that to configure the PPSIN for acting as a digital trigger, you have to edit the FPGA program of the USRP. But don't want to hassle with the FPGA program, I just want to do it by using the USRP API.

Your attached VI version is 14.0 and I have to run it in 12.0 so I have downgraded it by using Labview 2017. But after downgrading, an error occurs (See attached picture).

I have edited it by removing the enabled channel property node and tried to run it (See attached edited VI). But didn't get the required results as I am assuming the acquisition will be started on positive edge of digital trigger and when next positive edge arrives the acquisition restarts again. But it didn't trigger and ran in continuous acquisition mode and give the old result as I mentioned in my first post. Seems like PPSIN didn't sense any pulse.

I have acheived this task by using DAQ card. For a point of reference see the attached VI (DAQmx).

One more thing, I have also tried to input the trigger pulse using RXB of LFRX ( and Analog singal on RXA), because labview acquired the samples by using both channel RXA and RXB and forms I+Q signal, but I only got random noise on RXB, actually I swap both inputs. But didn't get anything from RXB on software.

If you have any questions please ask.

[Jorr-El]

Hi Rydaholic,

Could you point me to where you read that you needed to edit the FPGA program of the USRP?