logic analyzers under USD $500

Werner Almesberger werner at almesberger.net
Sat Nov 5 13:22:20 EDT 2011


Phil Endecott wrote:
> When I needed a logic analyser I ended up buying a Rigol DS1102CD.

Good choice :-) I have one too. Do you already know this ?
http://svn.openmoko.org/developers/werner/ahrt/host/tmc/
This package also includes protocol decoding capabilities.
Here it is decoding SDIO:
http://people.openmoko.org/werner/rigol/dxplore.png

.. and here full-speed USB:
http://downloads.qi-hardware.com/people/werner/tmp/teaser3.png

> I considered various PC-connected devices.  The main disadvantage
> was that I would need to also buy a Windows computer to operate
> them,

Indeed. They're basically all Windows-only.

> If you really only want to do I2C, I'm sure that there must be much
> simpler and cheaper devices that would work just as well.

Perhaps something like the Bus Pirate ?

http://www.seeedstudio.com/depot/bus-pirate-v3-assembled-p-609.html?cPath=61_68

When Rafa started working on Ben USB host, I looked into using
Ben+UBB as a simple logic analyzer. Unfortunately, DMAing from
PORTD has extreme jitter. Reading by software is slightly better
but very slow.

The best would be MMC, but there the choice would be between 1 bit
and MMC stream mode (which may produce a nearly continuous data
stream) or 4 bit and SD/MMC block mode. The latter has the problem
that each block is followed by a CRC, which will of course fail.
This in turn means that only one block can be transferred per
command. One could work around this issue with external logic, but
that would kinda spoil the "nice and simple" idea.

Of course, if we had a Ya+FPGA, making a killer logic analyzer
with it would be trivial ;-)

- Werner




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