|Chinese clone of a Saleae logic analyser. (Personally I think it’s taking the michael actually labelling the thing with ‘Saleae’!)|
I’ve been having trouble with I2C on the RasPi and asking around I was advised to try a logic analyser. I was a bit cynical about this as at first sight it seemed to be a rather expensive way to see digital activity on the I2C bus. I’ve looked at the I2C protocol and I’m not excited/interested in the nuts and bolts, protocols and timings of I2C, I just want it to work. Another guy recommended I slow the I2C bus down and use a normal logic probe to see activity, I have a very old logic probe a friend gave me many years ago and this was the path I started down trying to work out why I2C wasn’t working for me on my RasPi.
An aside – I think I’ve broken my RasPi…
In fact, the I2C of my RasPi appears dead. I spent hours researching and making sure I’d set it up right and on Les’ recommendation used Heeed’s I2C setup script (I also recommend it, it can be found here: https://github.com/heeed/pi2c).
When I run i2cdetect on the Pi I’d expect to see activity as the Pi queries the various bus addresses for a response. On my Pi the I2C pins never show any activity. I did try my I2C compass module at 5v on there, fully aware the Pi dislikes 5v but with an optimistic ‘I’ll probably get away with it’, maybe I didn’t get away with it…
I’m going to get a Pi A+ at some point soon and I’ll try again with that (being more careful with my voltages).
Back to logic analysers…
My friend advocating the Logic Analyser sent me a link to the one he was recommending: http://www.amazon.co.uk/gp/product/B00D5R8CUU I hadn’t realised the thing was just £20!
This is obviously a Chinese clone of the Saleae analyser with all of the risks that means. The one review I saw was negative, saying his was DOA and he had to get his soldering iron out to get it to work.
Another worry was the software to run it, the highlight of this unit is that it is compatible with the excellent software Saleae supply for their pukka analysers. More information here: https://www.saleae.com. I read some reports that the software had been updated earlier this year and no longer works with the clone analysers, but on further investigation there are clones that are even cheaper than this one and it’s them that have problems.
I decided to go for it and went with the one through Amazon.
It does what it says on the tin and at the right price
It took about a fortnight to arrive from China. It came packaged OK but with no manual and very cheap cabling.
The cheapness of the cables was soon forgot when the thing just worked flawlessly with the latest (beta) Saleae software (it also worked with the current stable version of the Saleae software, but the latest beta has many improvements and seems stable).
|The excellent Saleae software in operation showing a trace of changing PWM coming from an Arduino|
To test it I decided to play with PWM on the Arduino (and Micro Python – I hope to do a post on micro python another day).
|Arduino doing analogWrite (PWM) to pin 9 to fade an LED – Analyser is setup to monitor the PWM|
To generate a trace for the analyser to analyse I fired up the sketch associated with this tutorial: http://arduino.cc/en/Tutorial/PWM and got the trace above.
All in all £24 (inc postage) well spent, and I bet you could find this unit even cheaper on aliexpress (but be careful you don’t buy one that doesn’t work with the latest software: http://sunbizhosting.co.uk/~spiral/blog/?p=117 ).