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Maine
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I'm tired of feeling around in the dark, I need to go about getting an oscillosope and logic analyzer.

I've gone down the sound card oscilloscope path.  It's free, but it's certainly limited.  I was hoping for something a little more sophisticated.

I've looked at scopes and logic analyzers on Ebay.  None of them are tested, none come with probes and the shipping is really expensive.

I've also looked at some USB oscilloscopes and logic analyzers, and I think this is the way to go.  You can get a scope for around $150 it seems, and about the same for a logic analyzer.  The scope has no real requirements.

I'd like to fool around with some audio-related circuits, so I'll need something to visualize that.  It's also just a good thing to have.

I'd like the logic analyzer to have at least 16 channel to see what's going on in some of the computers I have.  I found one really good 8-channel (can't find it at the moment, it had an odd name) for pretty cheap, I might settle for that.

Does anyone own any of these USB scopes or analyzers?  I need some recommendations and direction on getting these tools.

I also thought I might make my own logic analyzer.  It's not that complicated I don't think.  You just need a fast clock source (16MHz or so), a programmable clock divider, a counter and some fast SRAM.  The arduino would control it all, of course.  I'm not sure how it would be triggered, but the clock controls the counter, the write latch on the SRAM and the data pins of the SRAM and connected directly to the probes.  It could work...  and would even be modular.  Each new module adding 8 more probes, requiring only another SRAM chip.  Though it would probably be easier to just buy one..
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I've played with the PoScope a little. It seems pretty useful, especially for microcontroller work.

Once you need to look at signals more than a couple megahertz, it's really inexpensive to pick up a Tek 465B and probes. I got one about 8 years ago for hobby work and it's never let me down. Ok, so storage would be nice, and I use that function of a digital scope at work all the time. It's just the cost issue: 100Mhz analog scope, good condition, $100 range. Good digital scope: order of magnitude more.
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it's really inexpensive to pick up a Tek 465B and probes.
Seconded, its a really good scope. Or go with the 468 which is the 465B with the digital storage option. There is one on ebay here: http://cgi.ebay.com/Tektronix-468-100MHz-Dual-Ch-Storage-Scope-READ_W0QQitemZ250365329008QQcmdZViewItemQQptZBI_Oscilloscopes?hash=item250365329008
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That's a little dinged up compared to how mine arrived...I even had the original manual and spare graticule. But the price + storage function is pretty nice.
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I wonder if you've explored the possibilities of finding a "scrap" scope that would be adequate for your needs?  I'm thinking of the sort of scope that gets routinely thrown out, working, by schools, colleges and businesses due to lack of calibration, lack of interest (!) or after being replaced by a new, shiny scope (that runs Windows, but lets not get into that here).  I've seen many find old scopes that get discarded like this, but are still quite useable for an amateur on something like the Arduino.

Is there a Dorkbot group near you?  Or any kind of Linux or amateur radio or robotics club?  If you can find a group like that, and join in, people will sometimes know where to find just the sort of thing you need.  Even FreeCycle is a possible source of old test equipment.  Don't forget to acquire old signal generators, power supplies, pulse generators, meters and so on, whatever is available!
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Maine
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@mem I'll watch that auction.  It doesn't end for a week, and if the bidding doesn't get too high, I might try to get it.  A tested scope is somewhat rare on Ebay.  Though this one seems a little messed up and comes with no probes.

@Anachrocomputer I have looked into this a bit.  There's not much where I live (in Maine).  There are HAMs around, maybe I'll try contacting them.  There aren't many schools around here that would have that kind of stuff, or businesses for that matter.  I did try FreeCycle once about a year ago, no hits.  I might as well try that again.
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I'm thinking of the sort of scope that gets routinely thrown out, working, by schools, colleges
Speaking as an employee of such an institution, that stuff generally gets surplused (sold at auction in lots).  Those things are expensive when purchased, and expensive things get tracked (long past the point when they still have value, in many cases).  You may have to look for a notice of a sale, buy a box/pallet sized lot, find one that works, then probably get probes somewhere else (since students seem to destroy them at an alarming rate).  Sell the remainder one at a time on ebay, maybe even making a buck along the way.

Businesses, on the other hand, may toss the stuff, or give it to an employee.

I already have a scope, but I'm watching for that US$150 USB logic probe to come out with mac/linux versions of the software.  I've had enough SPI and I2C problems that it may be worth it.

Hackaday has been featuring a few projects with a project known as the "bus pirate" (PIC-based, IIRC).  I haven't looked at it myself, but it could be worth a look if you're in the market for a digital signal analyzer on a budget.

-j
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Maine
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@mem:  I was able to find a reasonably priced, tested, somewhat recently calibrated 465B with probes and no missing dials on ebay.  I guess the stars finally came into alignment in respect to that.  I could have gotten it for a little less, but I used Buy it Now because I didn't want it to get away.

It's 100MHz, dual trace.  I've used a few Tektronix scopes before, these things are tanks!  Next month, I'll pick on a USB logic analyzer and then I won't have to guess what my circuits are doing anymore.
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@uzimonkey: congrats on that scope, it will probably last forever.

If you are interested in a logic analyzer of around the same vintage, the HP 1650B is a simple easy to use analyzer that you can find for very little money (although they are heavy so shipping can be significant) for example: http://cgi.ebay.com/Hp-1650B-Logic-Analyzer_W0QQitemZ330303804557QQcmdZViewItemQQptZBI_Analyzers?hash=item330303804557&_trksid=p3286.c0.m14&_trkparms=72%3A1205%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318%7C301%3A0%7C293%3A1%7C294%3A50

And the HP 16500 is  a more sophisticated (and complicated ) analyzer that also can be found going cheap.  This one is starting at $24.99 with  $39 shipping (its really heavy!)
http://cgi.ebay.com/HP-16500B-Logic-Analyzer-bad-hard-drive-w-16550A-Card_W0QQitemZ230321822018QQcmdZViewItemQQptZBI_Analyzers?hash=item230321822018&_trksid=p3286.c0.m14&_trkparms=72%3A1205%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318%7C301%3A0%7C293%3A1%7C294%3A50

The description says the hard drive is faulty but you can replace the drive. My 16500c drive went faulty shortly after I got it and I replaced it with a flash disk plugged into an IDE adapter.  I think you can still download the software from the HP Agilent site.

Anyway, a PC logic analyzer is probably more convenient and easier to use so don't let me tempt you into a complicated DIY repair project  smiley-wink

Good luck!
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Maine
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I was thinking of a more modern analyzer.  An analog scope is fine, but I want to be able to view and save stuff on my PC from the analyzer.  An analyzer is not a terribly complex piece of hardware, there are a number of smaller USB ones that will be great for me.  There's no need for an antiquated HP monstrosity there.

This one looks pretty good.  Only 8 channels, but they don't try to shaft you on the software.  There are some other ones like this (some with 16 channels) for a little more as well.  http://www.saleae.com/logic/

Though I was wondering, are there any with open source software?  Or at least software with a plugin interface to write your own analyzers?  I mean, this one only comes with a few protocols like SPI and I2C.  What if I need a different protocol?  Some companies try to shaft you and charge you $200 extra for a piece of software that was all of 50 lines of source.  Something I could extend myself would improve usefulness and longevity of the tool.
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Though I was wondering, are there any with open source software?  Or at least software with a plugin interface to write your own analyzers?
I've been lusting over the Saleae logic analyzers recently too. From what I remember they have an SDK that lets you write your own plugin protocol analyzers. And the software is soon to be cross platform - woot!

Andrew
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I finally gave in and bought myself a digital scope  ;D
Instek GDS-1022 for $350 from http://www.tequipment.net/InstekGDS-1022.html

It's an amazing piece of equipment for the money ! For Arduino work the 25 MHz sampling rate is all I need. It comes with 2 probes and an extra probe can be added to be used as trigger input. My only complaints are that scrolling through a long waveform is a bit slow, as is saving to SD card.

Of course the Saleae logic analyzer looks exciting as well and would make life easier for I2C protocol analysis which took me a long time with just a scope. On the other hand I found a bug in my program last night where an internal pullup was still active- easy to see with scope but harder to capture with Logic.
« Last Edit: February 02, 2009, 03:36:10 pm by Cross » Logged

Maine
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That certainly is more compact and modern, though nearly twice the price.  Still..  is that the price you paid new for it?
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Yep, that's new in box incl. ground shipping (and they messed up USPS shipping, so stick to ground if you want to go with that company). Let me know if you got any more questions smiley
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