Webserver client example using LabVIEW instead of browser
Posted: Fri Jul 01, 2016 10:17 amSomething like this may have been posted before, but here's an example (see attached, LV2014 SP1 Home version) of using the built-in LabVIEW HTTP protocol VIs (specifically GET) instead of a browser to interact with the webserver program. This saves having to learn any Java to program a nice UI in a browser, plus you get all the advantages of having a completely stand-alone LabVIEW program. I'm using a RPi 3 rather than a BBB, but the principle is the same. Also, in my program, I just have a digital input rather than an analog temperature input, but again it works fine for the example. My deployed application looks like this:
The only other change I make to the tutorial program is to set the output type for the digital input GET method to 'Text' (see below). This is not critical; it just saved having to do any conversion in the LabVIEW 'Client'.
Note that I found I had to deploy the code above as a 'Run at Startup' program to the RPi, using the instructions in this tutorial. The Webserver option also had to be 'checked' in the build properties. Then I had to close down the project before trying to run the 'client' program, or LabVIEW would continually try to redeploy to the RPi.
The next step was to build the LabVIEW "client". This is a completely stand-alone program, and can be designed separately in its own project. For this example I just used a simple producer-consumer design, with no error handling (so watch out for that). The block diagram is shown below, with the case for setting the LED also shown. It simply uses the HTTP 'GET.vi' function found in LV at 'Data Communication -> Protocols ->HTTP Client'. It just does exactly what the browser was doing in the tutorial, using the exact same text that was entered in the URL bar.
The case where the digital input is read is shown next. Again, it just mirrors what a browser was doing.
Finally, the front panel for the client is below. You need to enter the correct url and port number as dictated by your application. Also, the "body" indicator on the FP shows the result of the digital input when you press the Read Digital In button. It shows simple text because I set it to text in the webserver properties as mentioned above.
- Deployed VI.jpg (45.71 KiB) Viewed 1884 times
The only other change I make to the tutorial program is to set the output type for the digital input GET method to 'Text' (see below). This is not critical; it just saved having to do any conversion in the LabVIEW 'Client'.
- ws_properties.jpg (61.3 KiB) Viewed 1884 times
Note that I found I had to deploy the code above as a 'Run at Startup' program to the RPi, using the instructions in this tutorial. The Webserver option also had to be 'checked' in the build properties. Then I had to close down the project before trying to run the 'client' program, or LabVIEW would continually try to redeploy to the RPi.
The next step was to build the LabVIEW "client". This is a completely stand-alone program, and can be designed separately in its own project. For this example I just used a simple producer-consumer design, with no error handling (so watch out for that). The block diagram is shown below, with the case for setting the LED also shown. It simply uses the HTTP 'GET.vi' function found in LV at 'Data Communication -> Protocols ->HTTP Client'. It just does exactly what the browser was doing in the tutorial, using the exact same text that was entered in the URL bar.
- lv_http_get_bd.jpg (93.53 KiB) Viewed 1884 times
The case where the digital input is read is shown next. Again, it just mirrors what a browser was doing.
- bd2.jpg (29.49 KiB) Viewed 1884 times
Finally, the front panel for the client is below. You need to enter the correct url and port number as dictated by your application. Also, the "body" indicator on the FP shows the result of the digital input when you press the Read Digital In button. It shows simple text because I set it to text in the webserver properties as mentioned above.
- lv_http_get_fp.jpg (89.85 KiB) Viewed 1884 times