Author Topic: FPGA based logic analyser  (Read 7369 times)

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Offline GeoffSTopic starter

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FPGA based logic analyser
« on: May 06, 2010, 02:26:37 am »
I've seen mention here in the forums about low cost DSO's but not much about logic analysers.
I came across this little toy that may be of interest to someone who wants to get into FPGAs or simply someone who wants a cheap logic analyser for their home workshop.
The specs look OK:

  • 70MHz+ sample speeds
  • 32 channels
  • 16 buffered, 5volt tolerant channels
  • USB interface, USB powered
  • USB upgradable everything

 I've placed my order. Even if the logic analyser isn't up to the job, at less than $US50, at least I've got a cheap FPGA (Xilinx Spartan 3E) to play with.
 

Offline DavidDLC

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Re: FPGA based logic analyser
« Reply #1 on: May 06, 2010, 03:21:23 am »
I think that one is 16 channels, check this out for some comments if you haven't done it:

http://hackaday.com/2010/02/28/open-source-logic-analyzer-2/
 

Offline GeoffSTopic starter

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Re: FPGA based logic analyser
« Reply #2 on: May 06, 2010, 03:30:17 am »
The description on the Dangerous Prototypes website states:

A Xilinx Spartan 3E field programmable gate array (FPGA) is the central component of the logic analyzer. The FPGA samples data from 16 buffered and 16 unbuffered IO pins, and stores the samples in internal RAM. The samples are later dumped out a serial UART to the PIC, and from the PIC to a computer via USB.

The sample setups and screenshots only show 16 channels though.
Perhaps I should RTFM  :-[
 

Offline DavidDLC

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Re: FPGA based logic analyser
« Reply #3 on: May 06, 2010, 03:47:41 am »
You are correct with the description.
 

Offline Simon

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Re: FPGA based logic analyser
« Reply #4 on: May 06, 2010, 06:53:20 am »
the input header probably selects 16 channels at a time but for under 50 dollars it is probably a decent bit of kit to get started on, anyone wanting a cheap logic analyzer and scopr could have bought the rigol scope with analyzer I think the difference was not much more for a proffesional bit of kit ?
 

Offline wd5gnr

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Re: FPGA based logic analyser
« Reply #5 on: May 06, 2010, 12:15:47 pm »
I've used the software a good bit with the Spartan 3 starter kit (US$100 but way more flexible): http://www.sump.org/projects/analyzer/

Of course, that board is 3.3V only. The Dangerous Prototype board uses a level converter which is ok, but not really good at speed (even they admit that 5V at the top end of the frequency range is not so good). What's more is you can't vary the threshold voltage. One of my back bench projects I keep trying to finish is a converter board that does the conversion with a variable threshold. The design is sort of like my old Gould Biomation's front end (without the ECL back end) and only a little different from the Logic Cube's front end. See http://www.openschemes.com/modules/wordpress/2010/03/27/zeroplus-logic-cube-the-modification/2/. I'm not sure what they use for Vtrig but in my case I use a 250K resistor "in the middle" and wind up with Vt=0, 3.3V or 5V giving a lot of useful logic thresholds for the Sump's input.

Also I posted some new firmware for the Sump that has a trigger output (to drive, what else, the DS1052E ;-) ) at http://www.drdobbs.com/blog/archives/2010/04/homebrew_gear_p.html. I think the Dangerous Prototype one (which needs a slightly different FPGA load) already has a similar modification as well as an external trigger input which mine lacks.

Maybe this weekend I'll finish up my front end board.
 

Offline Grapsus

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Re: FPGA based logic analyser
« Reply #6 on: May 06, 2010, 06:19:21 pm »
Has anyone tried it? Although it looks very cool (FPGA for < 50$ !), I don't like this software, it's not intuitive at all...

They're out of stock at this time, so we'll have to wait :(
 

Offline charliex

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Re: FPGA based logic analyser
« Reply #7 on: May 09, 2010, 04:15:01 am »
I have the sump, and two of the gadget factory ones. The sump has more features, the GF one is cheaper.

the software basically the same, i use the omla so i have 5V on the sump, and it works quite well.

the GF is in active dev, where the sump is more spotty, however theyre mostly compatible.

i do often jsut end up using my intronix since its simpler and the software is better,
 

Offline GeoffSTopic starter

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Re: FPGA based logic analyser
« Reply #8 on: May 10, 2010, 10:43:05 am »
Has anyone tried it? Although it looks very cool (FPGA for < 50$ !), I don't like this software, it's not intuitive at all...

They're out of stock at this time, so we'll have to wait :(

The website still says that they're out of stock but I've just been told my order has shipped.

 

Offline Polossatik

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Re: FPGA based logic analyser
« Reply #9 on: May 11, 2010, 09:12:42 pm »
Just got one , basically mostly to play around with a FGPA...
First impressions are ok, might even be usefull as LA ...
Real Circuit design time in minutes= (2 + Nscopes) Testim + (40 +120 Kbrewski) Nfriends

Testim = estimated time in minutes Nscopes= number of oscilloscopes present Kbrewski = linear approx of the nonlinear beer effect Nfriends = number of circuit design friends present
 


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