Electronics > Beginners
Help Picking the Right Logic Analyzer
thakidd:
Hello all. Well I have been having a lot of fun with my Rigol DS1052E but ran into a problem the other night debugging a serial issue between an AT&T Motorola GoPhone and a Max3232. I did manage to solve the problem eventually by pulling some kung fu with the Rigol's run/stop button, but am wondering if I could have saved a crap load of time if I had a logic analyzer on my desk.
To clarify, most of my work is done between MCUs of the AVR variety and attached 'peripherals'. I am wondering what kind of logic analyzer I should be looking at. I am on a limited budget but would prefer to buy something better now than have to re-buy later. I am also about 3 to 6 months away from jumping out of the Atmel 8-16bit stuff and possibly playing with the Atmel ARMs.
I have looked at all of the USB logic analyzers and, after some research, found seriously issues with their bandwidth. I have also checked out the Open Bench Logic Sniffer which looks like a better option than USB type stuff (@ +70MHz) and it appears that GadgetFactory has come out with the Butterfly One which does 100MHz and possibly 200MHz.
So what do you recommend? Is there something nice I might build myself (i.e. +100MHz; better than the Seeed OLS)?
Thx for your suggestions in advance.
slburris:
So the first questions you need to ask are:
1) How many signals do you want to monitor simultaneously?
2) What's the highest clock rate you need support for?
3) Do you want stuff that does protocol decoding for you, i.e. SPI, I2C, and the like?
4) Standalone or use a PC?
5) What voltage levels do you need to look at? TTL, 3.3V CMOS, 2.5V CMOS, something else?
Scott
thakidd:
1) 32 signals
2) Not sure..currently playing with AVR Megas but am considering moving to AVR ARM
3) SPI, I2C, etc would be quite nice as I do use them a lot
4) PC preferable...may not be necessary though
5) All of those...I believe I would never analyze something over 5V or so, but I could be mistaken.
TBH, I am not sure what I need. At this point in development, I would say I need something simple to diagnose 8-16bit MCU peripherals...but moving to 32bit is a whole new world to me that I am just starting to explore. I can tell you that currently a logic analyzer capable of max 200-100MHz on 16-32 channels should work fine. Not sure though if that will suffice for the future. I guess I am looking for a device with a bit of growing room when it comes to USB, etc...at a reasonable cost of course.
slburris:
The big problem with the open source logic analyzers I've seen is that they are little
more than FPGA's with memory attached. That's fine if what you are working on
fits nicely with I/O voltages of the FPGA. If it doesn't, what do you do? I'm not
sure how reliable just exposing the FPGA pins with no input conditioning is going to be.
Given your clock requirements, none of the USB analyzers that stream data to your
PC's memory are going to cut it. You need stuff with onboard memory for capture
that can later be sent to your PC.
Have you looked at the Intronix LogicPort? 34 channels, sampling to 500Mhz,
decoders for CAN, I2C, SPI and RS232. The logic threshold can be adjusted from
-6 to +6 volts and I think it can tolerate +- 40 volts without breaking.
http://www.pctestinstruments.com/index.htm
The downside is that capturing is into an internal block RAM on an FPGA (for speed)
so you only get 2K of memory. However, only transitions are stored, so that can
give you a lot of effective compression, depending on what you are looking at.
There are also some cheaper clones out there, but I've heard the software isn't
nearly as good as the Intronix software:
http://www.thefamousbrandsoutlet.com/test-measurement-instruments/pc-usb-logic-analyzer/pc-based-usb-logic-analyzer-la5034.html
http://circuitspecialists.com/prod.itml/icOid/8251
Alternatively you could take one of the open source FPGA boards, add some sort
of input conditioning to let you adjust the logic thresholds and roll your own.
Scott
TheDirty:
Do you really need that much bandwidth for a logic analyzer? I have a USB one and I've never been limited by its bandwidth. 99% of its use for me has been interface and protocol decoding. I suppose if I ever had a problem with the signals going too fast I can always artificially slow them down in code in order to debug them.
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