Looking for a USB logic analyzer - suggestions?

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Looking for a USB logic analyzer - suggestions?

Postby nezb » September 12th, 2012, 8:01 pm

Hi everyone,

I'm a computer science guy, doing some work with FPGAs, and I'm looking to buy a logic analyzer. I'm fairly convinced a USB one is the way to go, so I can bring the waveforms into my computer for analysis. I don't need something super fancy/expensive, and I was looking at the Saleae Logic (http://www.saleae.com/logic) and the Open Workbench Logic Sniffer (http://www.seeedstudio.com/depot/open-w ... p-612.html).

I'm looking to hear what other fellow hackers use, and their thoughts on what the best choice is. Thanks!
Last edited by nezb on January 25th, 2014, 3:45 pm, edited 1 time in total.
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Re: Looking for a USB logic analyzer - suggestions?

Postby semicolo » September 12th, 2012, 8:55 pm

I don't have any of these boards but I find the first one a bit slow, nowadays you'll probably be faced with signals faster than 24Mhz pretty often
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Re: Looking for a USB logic analyzer - suggestions?

Postby nezb » September 12th, 2012, 9:08 pm

Yeah, that's one of the things I was worried about. The Salea looks like it has some amazing software, but unfortunately the hardware seems very highly priced for its specifications.
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Re: Looking for a USB logic analyzer - suggestions?

Postby Osgeld » September 12th, 2012, 9:22 pm

I have the open logic sniffer, I got it from sparkfun on freeday, it functions, its faster and cheaper than the saleae, but its a junky pain in the butt overall, and if it wasn't free I would have sent it back.

"Capture 50MHz+ waveforms on 32 channels"

But only 16 of them are buffered, so unless your probing something at the same voltage level as the FPGA its 16 channels, likewise the 32 channels are on the same 16 pins and you choose inner or outer, so in combination that claim seems a little grey.

last time I checked RLE doesnt work right, and the "probes" are just mini-grabbers on ribbon cable, which I find to be a massive pain in the butt to use as the wire sticks directly out of where you push down, and I have had to resolder a few here and there. They also dont grab all that well, and its quite easy to knock them off of something as simple to hold as a leg of a dip chip.

You have to ground unused probes or else they echo like crazy, and there's no real good place to attach them to ground. You also have to buy the "probes" separately, you get no enclosure, and the only 2 mounting screws are in a poor position, I just used some self stick rubber feet, but of course since its just a board its not uncommon to watch the USB cable drag it off the edge of the desk, and pop all your connections free.

It functions, its cheap, you just got to fiddle fart with it, constantly.
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Re: Looking for a USB logic analyzer - suggestions?

Postby nezb » September 12th, 2012, 9:29 pm

Osgeld: *sigh* that's exactly what I feared, and you describe exactly the thoughts I had dealing with other low-budget purchases. Also, LOL at "fiddle fart" :D

It's a shame, really, because I'd be willing to pay double the price of the OLS to get something of better quality and still be able to support open hardware!

Do you know of any good competitors to the Saleae Logic? I can't imagine they're the only player in this field, but I can't seem to find anyone else. Perhaps I am not looking in the right places...
Last edited by nezb on January 25th, 2014, 3:45 pm, edited 1 time in total.
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Re: Looking for a USB logic analyzer - suggestions?

Postby UAirLtd » September 13th, 2012, 8:11 am

I have the Saleae logic analyzer to do some basic logic probing work (mostly debugging data busses), but semicolo is absolutely right, on a few occasions I have found the sample rate too low (the actual sustainable rate is something like 16MHz)

The Salea software has a very nice-looking GUI, its features are fairly standard - a scrollable zoomable display, different recording sessions in tabs, options to resolve various serial protocols (I2C, SPI, etc.) in hex or ASCII, the usual triggering options, measurement data (frequency, duty cycle, times, etc. etc.), various save/export/screenshot options. I wouldn't expect any more in terms of features from logic analyzer software, and I commend the interface for being very well presented and very intuitive and easy to use. You can download their software to try it out, it comes with a "simulation" mode which allows you to explore the various features.

On the physical construction, the Saleae is much smaller than it appears on the picture, being a nice 43x43x9.3mm anodised aluminium box with semi-rubberised underside. The 9 probes (8 channels and ground) come as a bundle of wires on a single 9-pin 0.1" pitch socket that plugs into the recessed headers in the device itself, cables and probes are of good quality, wires are probably a lot thicker than they need to be for a probe, but convey a sense of robustness. The probes themselves come separated from the cable, whose ends terminate in a heat shrinked connector, but it takes mere moments to plug the wires into the probes, the connection is solid and there is little chance of accidental separation. The probes have grabbers with 0.43mm width and have no problems latching onto pins or wires. The 9th probe is a ground connection, though the whole thing is grounded to the USB ground. Everything comes with a zip-up case that is far too large for it, and a high quality and surprisingly long USB cable.

On the balance, a great logic analyzer for basic work, if you don't need sampling beyond perhaps 16MHz. The construction and feel of the device itself is excellent, and I would expect it to last some time. Overall for my purposes I believe it was a good investment, it is hassle-free, pleasant to work with, with only a slight regret at the sample rate.
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Re: Looking for a USB logic analyzer - suggestions?

Postby martinmunk » January 22nd, 2013, 10:23 pm

I've had the Saleae Logic16 for quite a while and the software is simply brilliant!

If i'm running nothing but the Logic on the USB controller i've never had i problem at the full speed of the device.

With the 16 pin model you get the ability to do 2 channels at 100MHz or 4 at 50.
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Re: Looking for a USB logic analyzer - suggestions?

Postby st2000 » January 25th, 2013, 8:59 am

Hum, let's turn this on it head.

So you're designing circuits in an FPGA. Probably using VHDL. But you're a software guy. So, why not write the equivalent of a debugging library for your FPGA design. That is, put some VHDL code in there to grab states and store them away in a bit of memory. Then pull them out later over another VHDL "debugging library" serial port. You could write some software in any number of languages on your desk top to display the results. Opensource and document your efforts and we'll all be happy :)!

-good luck
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Re: Looking for a USB logic analyzer - suggestions?

Postby nezb » January 25th, 2014, 3:42 pm

Had the Saleae for a while (bought through Adafruit - east coast reseller), just posting here that it has been an excellent tool for debugging communication protocols between devices

st2000 wrote:So, why not write the equivalent of a debugging library for your FPGA design.

Altera chips have a feature called SignalTap, which does this. It is powerful but not as simple as a LA. I have not used Xilinx's equivalent tool called ChipScope.
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Re: Looking for a USB logic analyzer - suggestions?

Postby tonyarkles » February 7th, 2014, 6:38 pm

Another option would be to use an FPGA board to do the capture and sending it back to your computer. I think the logic would probably be pretty simple: a small state machine for triggering, RAM to store the captured data into, and then a simplish way to get the data back out (high speed USB uart?).
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