Off the cuff, as I see it. These are my personal comments and represent my opinion
pridopia "Raspberry Pi Rs-Pi I2C 23017 x2 32 bit GPIO Board"
I bought one of these boards off ebay. Quite pricy at £25ish . Probably cheaper to blow a pi than to buy 1 of these
Anyway. It does what it says on the tin. 4 ports of 8 bits accessable from the pi.
Ports (or bits) can be set to be in or out under software control.
The "manual" that came with the unit was 1 page of pretty poor double sided A4 b/w paper.
Dont actually expect it to help you unless you know what you are doing. It starts "If you already install I2C driver , then". And if you have not? They did show you how to get a python module
I am a C programmer not python, so I had to find and download some 23017 drivers.
My kernel is raspberrypi 3.2.27+ so it has i2c support (all be it disabled in the modprobe start up files)
Anyway changed those files picked up the i2c tools (apt-get install i2c-tools)
Something not right on my config and I have to do "modprobe i2c-dev" each reboot until I figure out what is not probing.
Then I got some c source code for userspace drivers
wget http://www.open.com.au/mikem/bcm2835/bc ... .13.tar.gz
nice drivers, did what it says on the tin -fits in well with the pridopia board.
I also downloaded the code from http://alanbarr.github.com/RaspberryPi-GPIO/index.html
That too does what it says on the tin (but I could not find a wrapped up package and had to
cut copy paste about 5 wee files). However all compiled up and ran A OK.
Not cheap, manual short of advice, web page reference to nathan.chantrell.net - nice page but a lot of digging needed. A package this price should have a nice dedicated web-page to make it easy to set up.
I would recommend the board to anyone needing to breakout more than the RaPi will do and/or
who needs 5v i/o.
The pridopia board has one flaw. There is no easy access to an earth pin on the board.
The 4 x 8 pin connectors that can be set up to do in or our are delivered on a 8 way 0.1 pitch connector. Great but if you are using the 2 x 13 header for other things finding an earth is not easy. Ditto if you are looking for a +5 to handle some pullups.