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The Slice of Pi/O gives a Raspberry Pi an extra 16 buffered inputs or outputs. There's now quite a few people making boards with the MCP23017 driver chip on so there's lots of code examples about. We think our baord represents some great lateral thinking and superb design. The main features are:
Dimensions: 35.5mm x 51.5mm x 18.9mm
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Posted by Kevin on 20th Oct 2012
As a board, reasonably easy to assemble (even with my inexpert soldering skills). Opens up lots of options for safer experimentation than connecting things up to the PI directly.
To improve, maybe repeat some of the MCP23017 info in a more Slice of PI/O specific way to help people get started using it, e.g. adding a few LEDs for testing and including some more info on things like the power jumper.
Posted by Steve Farrage on 13th Sep 2012
A great add-on for the Pi. Very easy to assemble and perfect for expanding the GPIO abilities of the Pi from the standard header.
Providing you check which version of the Pi you are using and therefore select the correct channel you should be good to go.
How could it improve? Well, it would be good to include some additional header pins for the daisy chaining element, and watch out for the incorrect labelling of B0-B7 as they are the wrong way round. i.e. B0 is actually B7 etc. It took me a couple of days of head scratching before I went back to basics to look closely at the tracks to see where they went. At this price it's worth having a few of them at hand.
There's a note in the build doc about the miss labeled pins and this will be corrected in the next batch of boards.
Posted by David on 13th Sep 2012
Nice Kit. My only grip is that the hole by the free end of the board is in a bad place. Half over a very very tiny component, C12 on the Pi, so if a nylon screw (not supplied) is used as a pillar to stop the board shorting on the can by RG2 then it could easily damage C12.
Posted by Bryan Dredge on 9th Sep 2012
Easy to construct and components nicely laid out. Potential gotcha for Pi Revision 2 users, they have swapped the I2C channels so the I2CDetect command as shown won't show the board, you need to change the zero to a one in the command I.e. i2cdetect -y 1. Wasted some time re-checking all my soldering before remembering reading something on the pi blog.
UPDATE: Documentation is here http://openmicros.org/index.php/articles/94-ciseco-product-documentation/raspberry-pi/223-slice-of-pio
Posted by Unknown on 23rd Aug 2012
I am a complete novice and have built my Slice of PI/O board as shown. I have soldered the three pins to give me an address of 0x20 and this works fine.
I have three questions that I hope someone will answer:
(i) Nathan says of his board
"Note: Make sure pins 15,16,17 of the MCP23017 all connected to ground (the 3 pins top left of the diagram, shown linked in blue).
Is this still necessary, or does this board prevent the problem?
(ii) Am I correct in thinking the pinouts on the PI/O labelled A0 to A7, and B0 to B7, each have their own ground pin beside them?
(iii) Which of the pins on the board equates to the 5v and GND on the Pi?
Thanks in advance for your help.
CISECO : Hi you didnt say who you were, would you either put a question on the forum or reply to your shop/ebay order.
Posted by ryniker on 17th Aug 2012
The product page should contain a link to the construction details:
The "4 wire daisy chain connector (PWR/GND/SCL/SDA)" is not explicitly identified. It should contain at least one additional wire, for connection to interrupt pins on downstream boards. It is not really difficult to identify the 4 pins, but it should not be necessary. There should be an illustration of the recommended connection.
Because the 26-pin connector to the Raspberry Pi can be installed in two orientations, there should be identification of the pin 1 location. The product image shows clearly the board should be positioned over the top of the Raspberry Pi, but with two ways to connect it, I can imagine it will sometimes be plugged incorrectly.
It looks like the circuitry beneath the Slice of PI/O might contact the metal can labeled C6 on the Raspberry Pi (the RPi sechmatic suggests this might actually be C3). There is normally some clearance at this point, but the assembly is not rigid and might flex enough to short when a connection is made, particularly to a bank B pin. Some insulation on the top of this can, or on the bottom of the PI/O board, should prevent a short.
Finally, the GP0 ... GP7 labels are inconvenient. It would be better to use the Broadcom GPIO pin numbers, because that is what a program typically needs to use to control these pins. At the very least, document which pin on the 26-pin RPi connector is routed to GP0, GP1, etc. I can use an ohmmeter, but it ought not to be necessary.
Despite this, it is a neat little device, at a very reasonable price.