Beginner's logic analyzer?

Question

Can anyone recommend a low cost or DIY buildable logic analyzer?

Mostly, it would be for debugging serial protocols (SPI, I2C, RS232) at low voltages.

Answer 1

The Bus Pirate is probably your best bet - open source software and hardware, easy to build if you don't mind SMT, cheap if you buy it assembled ($30 shipped worldwide).

http://code.google.com/p/the-bus-pirate/

Lots of variants, with a lot of people supporting it:

http://www.google.com/search?q=bus+pirate

The bus pirate is mostly useful for serial work, though it can do some small amount of simple logic analyzer functions. If you need to do a lot of logic analyzer work, this product looks very nice:

http://dangerousprototypes.com/open-logic-sniffer/

Open source, but has very good capabilities. Very inexpensive, though.

Answer 2

Not sure if this matches your definition of low-cost but the Saleae Logic Pod is around $150. Eight channels and works well for decoding SPI and I2C. Haven't tried any other protocols.

The software is OK but the interface seems a little strange compared to an oscilloscope or real logic analyzer. On the website there was mention of an API definition so that you could write your software interface or scripted data collection. I haven't had time to look into this any further.

Not sure if the levels go negative for true RS232 work.

Answer 3

There is the Sump.org logic analyser, using a low-cost ($99) Digilent Spartan 3 board.

For slow stuff like I2C and SPI, you could use a Microchip PICkit 2 ($35). It comes with three-channel logic analyser software.

Answer 4

As far as actual logic analyzers go (versus something like the Bus Pirate), I wrote a basic comparison of (relatively) inexpensive ones:

Comparison of PC-based logic analyzers

One thing to note about sampling speed, a rule of thumb is you generally need at least 4x your data rate in order to get an accurate reading, and up to 10x is better. So if you want to monitor a 8MHz signal (which you can easily generate from an inexpensive AVR in SPI for example), you'd want a 32-80MHz sampling rate analyzer. This only applies when capturing in 'async' mode. If you are capturing in 'synchronous' mode (eg with a clock signal), then your sampling rate only needs to match the rate of the clock signal. So for example in that case, 8MHz synchronous sampling would be enough to capture a 8MHz SPI signal (since it has a dedicated clock signal).

Answer 5

I stumbled across this at www.seeedstudio.com

Open Workbench Logic Sniffer (pre-order only)

I really don't know anything about it beyond their description. It might be worth looking into.

Answer 6

A little more expensive ($389) than the ones mentioned so far, but very capable:

Logicport by Intronix

34 channels Adjustable logic threshold (+6V to -6V) I2C, SPI, RS232 and CAN interpreters

plus the software can be run in demo mode before you buy it.

Answer 7

The pickit2 has a simple logic analyzer (as well as a programmer for pic uC's and a UART tool)

Answer 8

Scanalogic 2 is, well, less expensive than many other logic analyzer, but it's worth the 59€ i think

http://www.ikalogic.com/scanalogic2/

Answer 9

The scanalogic is a simple but nice 4 channel logic analyzer.

http://www.ikalogic.com/scanalogic_home.php

Answer 10

What is also interesting is the open sourcing of the software to run the devices.

The bus pirate is on the list and coming along if you look at the commits for SiGrok

http://sigrok.org/wiki/Main_Page

Answer 11

I use a BusBee. The hardware/software is very simple to use and it can log a lot of data. Works on many different protocols, but I typically use it for I2C.

http://www.usbee.com/busbee.html

Answer 12

Open Workbench Logic Sniffer

I bought it and it works great, I'm not sure if they are still preorder but I think it is exactly what you're asking about. :D

Answer 13

I use the logic analyser from saleae (http://www.saleae.com/home/). It's very good and works fine. It's priced at US$ 149.00.

Answer 14

This answer is rather late for the original question, but a new product, and an excellent little device is the Gabotronics xminilab, ref:

http://www.gabotronics.com/development-boards/xmega-xminilab.htm

It is an analogue, two channel 'scope, a waveform generator, and an eight channel logic analyser/protocol sniffer (it shows not only the waveforms, but also the hex values on the channels). Sample rate is 2 MSPS, so it is only good for about 200kHz, but its cost at about $69 means you get all these features in one cheap package.

I have no connection with the firm except as the owner of a couple of the xminilab's smaller brother; the xprotolab, claimed to be the world's smallest ..., with a tiny screen, a novelty and fun, but you need the bigger screen of the xminilab for serious work.

Answer 15

Please also take a look at our LA-08, an 8-channel logic analyzer with I2C master and I2C SPI UART decoders. LA-08 is priced at $99. http://www.ideofy.com/la-08_en

LA-08 (comparing to similar products) has the following features:
(1) Faster sampling rate. LA-08 can do 30MSPS @ 8-channel, 60MSPS and 96MSPS @ 4 and 2-channel, respectively. Faster sampling rates allow you to measure time more accurately, as well as to deal with signals of higher speed.
(2) Wide input voltage range. LA-08 takes input signal from +16V down to -0.7V, and remains undamaged even if -5V is applied to input pin(s).
(3) I2C Controller. LA-08's built-in I2C controller allows you to send commands to i2c slaves. This is useful when debugging I2C related issues.

With the low price and the adquate features, we consider LA-08 fit the beginner's needs for a logic analyzer.