waveform display in browser

I'm halfway through doing almost exactly this; a waterfall spectrum display. The data comes from real-time FFT (similar to Jan P's project) and one line is passed every 5ms as JSON into the web browser. The web browser accumulates packets and uses the browser's requestAnimationFrame to get a guaranteed time to render the content before the screen draws. Use the timeline tab in Chrome devtools to see how long your JS invocations are taking, and make sure you're not trying to do too much work in between frames. The animation frame rate will be a fraction of your display refresh interval, often a max of 60FPS, otherwise 30, 15, etc. Both HTML5 Canvas and SVG are fast enough though, if you do it right.

There's a graphic trick to make a continuously sliding waterfall. Mine slides sideways, not downwards, so I made a DIV twice as wide as the frame, and draw every vertical data line twice, separated by the width of the viewport (so one copy is off-screen). slide the underlying window one pixel sideways for each line you draw, until you hit the limit when you jump it back to the start.

I'm not available for this as a consult, and it's not my main project at the moment. But you've seen my impedance nomograph, so you know a little of my capabilities: .

I hope the above helps you. Contract prices for good front-end programmers who are capable of doing this kind of stuff well are pretty crazy.

Clifford Heath.

What's the matter with that?

I think they want to use JavaScript. This is interesting:

An easy method for non-programmer types is this:

Comes in various flavors from free to full bore. A "Shazam!" reaction at a client happened when they found their company logo integrated into the control screen which was no more effort than copy-paste.

There are a bunch of options but unfortunately Javascript seems to be the only one that's actually practicable. Try this:

Den torsdag den 23. juli 2015 kl. 20.18.16 UTC+2 skrev John Larkin:

long time ago when I hacked together the plotting for your cabin temperatures

I used

-Lasse

One approach is a CGI script that runs gnuplot under the covers. IIRC quite a few folks do that. (I'm a static HTML guy myself.)

Cheers

Phil Hobbs

Isn't there an actual oscilloscope display package under Linux? It should be fairly straightforward to drive that from an internet connection. I guess requiring the customer to installing such a package is not preferred.

He is after a browser plugin - something like VNC, the way I do it on our spectrometers (I do not use a plugin but I could if I wanted to).

However this implies a fullblown RFB connection to a stand alone system having its display and GUI locally (within his oscilloscope thing) which is far from being trivial.

Dimiter

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Den torsdag den 23. juli 2015 kl. 20.18.16 UTC+2 skrev John Larkin:

buy a red-pitaya:

it is a zynq running linux and it seem to do exactly what you want

-Lasse

I still log the cabin temps using gnuplot. Did you furnish that script?

Now that looks promising. Thanks.

We're not planning to run Linux on this product; it will be a bare-metal LPC3250 and an FPGA and a bunch of analog stuff.

Serving up the html and javascript doesn't look difficult. The scope display is probably not difficult for people who regularly program this sort of stuff.

I've used a JS graphing package called "flot" that could probably be modified to display scrolling or static waveforms. I think it's based on HTML5 canvas and/or SVG DOM. I made some small tweaks and found it to be well written.

Yeah, I get what he is after, but there is more than one way to skin a cat. Another would be to allow a remote desktop connection. Then no software of any kind is needed for the client other than the RDP app. Still more work on the client end but installing a canned app isn't that hard. Browser based apps can be work to get running on multiple browsers and keep running with browser updates. A friend is in that line of work and there is *soooooo* much work keeping all the different versions working.

Actually, I don't want a plugin, just a way for the browser to display a waveform, using some javascript. We can store any reasonable zipped javascript libraries in our gadget and deliver them to the browser.

The tach box will have no display or GUI, and in fact no official OS.

Den torsdag den 23. juli 2015 kl. 23.22.23 UTC+2 skrev John Larkin:

yes, it is just a tiny bit of php to convert the logfile to data strings in the right format and generate the html with that data and using flot

-Lasse

I am not sure I have seen that done for live graphics - then scaling, perhaps autoranging etc., even if doable it would be a massive pain to support with all browsers as they keep on evolving. Your best bet might be to produce locally a .gif (or .png or whatever) bitmap, maintain it live and persuade the browser to refresh it regularly. Don't know how the latter is to be done though.

Not having a display is not a problem, some of our spectrometers do not have one, they just maintain the display bitmap in system memory - which is viewed via RFB (VNC)(RDP which Rick suggested is very similar, same thing really but over a non-public protocol). Not having an OS - nor a VNC server nor the image to be displayed - obviously makes this impractical in your case.

Dimiter

------------------------------------------------------ Dimiter Popoff, TGI

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We could do that in the FPGA! If nobody murders me for suggesting it.

Lasse also suggested flot. That looks promising.

Wanna help?

If a simple GIF image is good enough, I'm pretty sure you can imbed that in an HTML page that will auto refresh periodically. How often does it need to update?