Low speed O-Scope

Philldapill

I know Parallax has been making a mid-high quality Oscilliscope, and will be selling it soon. I'd love to get my hands on one, but lack the funds at the moment. I'd love to try and build a low quality one for some of my simple purposes, but I don't have a way to output the data to a visual image. I've been tinkering with ADC's and Current Sensors for a while now. I can display the values as numbers on the TV, but I'd like to be able to output a realtime graph of the values. I'm not looking for a 20MHz scope... Just something that can display a realtime graphical display of the data. I'd like to be able to adjust the sweep time, but that is more of a programming thing on my end.

So, what graphics objects would be best for this? My objective is to have a TV output that resembles the screen of a scope, but I'm not worried about it being cute... I just want to update at 30FPS if possible and have it double buffered.

Rayman

You might start with the microphone2vga example... Shouldn't be too hard to convert it to TV.

Or, just use Graphics.spin to plot points...

virtuPIC

Right! microphone2vga is a very good starting point. It's a great demo for non-propelling people. Load it to a demo board without additional hardware and see your voice on a monitor. It tells you about triggering and syncing the screen to the signal. It also shows you how to write a signal curve to a screen. I would also be interested to have it with TV output. Yes, I know, I could do it myself. But I am on other projects currently...

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Ale

Here is my humble FFT demo that also displays the signal.

I'll upload it to the OBEX shortly. As soon as I comment it a bit better and make the MIT license in.

In this case it is all done in one COG. But once the signal has been acquired you can easily use one COG for FFT (if desired) and one to display the signal. You make a copy of some 250 or more points and display them and use more points to calculate FFT (1024 in this case). I can provide more feedback here if you want.

Depending where you are you can get some 320x240 or 640x480 (can be used as 320x240 because the dots are really small) mono LCD that can be conveniently driven with the propeller and use it to display the signal. Here in germany I can get for 10 Euro a mono 640x480 display that can be driven with the prop directly, no extra controller needed. (I posted tis code some time ago).

This works with a 1 Msps ADC. But you may use any ADC you have around. Btw, it is pure pasm

Have fun,

Ale

Edit: rename to .zip in lame OSs

Post Edited (Ale) : 4/30/2009 9:52:44 AM GMT

Danico

Ale,

Very interested in you FFT demo, have been trying to come to terms with it on the wiki, seeing it as an operation program makes things much clearer.
Am working on (yet another!) audio spectrum analyser, for which the FFT routines will be the heart.

Initial question is regarding the ADC used, in your code it says AD9832, but looking at the Analog Devices web site, this is a numerically controller oscillator (DAC), so something not right with the part number?· Am I looking in the wrong place?

Don't want to hijack the thread, but I would like to come to terms with the use of this FFT software.

Thanks,
Dave

Ale

Sorry Danico, I wrote the wrong number :-(, it should have been an AD9283. I'll correct the file.

Edit: Corrected

Post Edited (Ale) : 4/30/2009 9:53:16 AM GMT

Danico

Ah, now that makes more sense!!

Will work my way through the code, and I'm sure many questions to follow.

Thanks for doing all the hard work on this!

D