Zaurus Oscilloscope, using commercial hardware Options

[jfr]

This post is a trawl, to see whether there's any wider interest in an oscilloscope project I've been working on.

The project uses a digital scope manufactured by Syscomp - the DSO-101. It's a two-channel scope, which plugs into a USB port and uses the conputer as its driver and display. You can read lots more about it at Syscomp's web site.

What I've been doing is to port the host software to the Z.

I bought the scope in the first place in connection with a Morse-to-speech project (mentioned before in these forums). I liked the spec and the price, and I particularly liked the fact that the software that runs on the host is open sourced. The software is written in Tcl/Tk, and I've been porting the main functionality to C++/Qt.

The scope hardware is physically bigger than a Zaurus, but not by all that much, so I thought it would be neat to use the Z as a host and thus end up with a pocket-sized oscilloscope system.

I've now got the port working pretty much to my satisfaction (YMMV). The port doesn't have all the advanced features of the original software, but I think it does count as a workable system. My Zauri are still using their original Sharp ROMs, and the program should work on C1000/3000/3100/3200.

(Dis)claimer: When I first bought the scope, I was merely another customer for Syscomp. I then offered them a couple of contributions for the host software, and that progressed to the point where I became a beta-tester for them. From that, I discussed the idea of the Z port and they were immensely supportive, including supplying extra hardware for the purpose. From that, you'll correctly gather that I think these people are Good Guys. But I have no commercial relationship with them - this is an open source project, pure and simple.

Maybe this is just my private toy, but if anyone else would be interested, I'd be happy to share it.

Cheers

John

[Ragnorok]

- Neat! I've been looking for a DSO to do transient capture, but so far I haven't found one that appears to be what I'd need, mainly because the capture buffers are so darned tiny. But I could very well be wrong ... I have a Tektronix lab 'scope I use right now and I'm not so familiar with DSOs.
- I'm very, very interested in two things:

1) Can this DSO do transient analysis even with that tiny 32k sample buffer? At 20MS/s that's a minuscule slice of time, so on the surface it looks inadequate. But it very well could work somehow that I'm not aware of, in which case I'd be very, very interested to hear it.

2) This port. I really like the idea of using the Z as a portable o'scope. Very spiff!!

Details:

- I'm doing work with goto control systems for amateur astronomy, and I'd like to analyze the power rails for transients introduced by the pulse-width-modulation drive for the motors. Some goto mounts are very finicky about supply voltage, and I think it's actually because they put too much noise on the rails. My thought for analysis was not to trap individual transients, but to capture supply voltage and current data (using the two channels) and see where to goto crashes. It's the transient that causes the goto system to wonk out that I need to see. I was hoping a DSO would do the trick but nothing I've read indicates they will because I haven't seen any affordable ones that will capture 20MS/s continuously. They all do it 'til their buffer is full, then you're sunk, or at least that what numerous owner manuals seem to imply.
- I'd love to wrong! I'll buy one of these things, no problem.

- Thanks for your time...

[jfr]

1) Can this DSO do transient analysis even with that tiny 32k sample buffer? At 20MS/s that's a minuscule slice of time, so on the surface it looks inadequate. But it very well could work somehow that I'm not aware of, in which case I'd be very, very interested to hear it.

Sorry for this slow reply - I've been distracted by $DAYJOB.

You can't use the DSO-101 for continuous sampling in the sense I think you mean: you'd have to read a 32K sample set, then tell it to go and get another one, and so on. But what does happen is that while it's waiting for a trigger condition, it will be continuously collecting samples and when the trigger occurs you'll have 16K samples from before the trigger, and 16K after it. In other words, that 32K is a circular buffer, and I think that's the key here.

The issue, then, is how to trigger the scope when the crash happens. You say you want to monitor both supply voltage and current, using the two channels. If you're doing that, then the only way to capture the event is to detect the crash, and send a manual trigger command to the scope when it happens. That would mean modifying the software. To go further with that idea, I'd need to know how you detect that a crash has occurred. As an example, though, I don't think it would be hard to modify the software to accept a signal from another program as a trigger command. The difficulty would be that there would be latency involved in such a system.

But if you were prepared to monitor just one of those variables at a time, then you could monitor it on channel A and trigger from channel B in single-shot mode, if channel B could be connected to some source that would act as a crash detector. That would be my favourite solution.

More generally: if you go to the Syscomp website at <a href="hhttp://www.syscompdesign.com/">http://www.syscompdesign.com/</a> and look in the Downloads section, you'll find a link to my software as an ipk file, together with some descriptions. I haven't yet put the source code on there, mainly because I haven't yet got round to documenting the rather complicated build process. But I do confirm that I'm perfectly willing to share it for free. In fact, if you or anyone else wants to work with it, PM me and I'll send the source to you and work with you on the build process. That way, the documentation will get done. The build is a cross-build on a Linux desktop.

Also, I think if you contact Syscomp directly (the email address is on their website), you're likely to receive informed answers to questions related to (and not of course limited to) astronomy.

Obvious disclaimer: Syscomp are not responsible for any inaccuracies in this post.

Hope that helps.