Raspberry PI I/O expansion

Last update: 1/05/2015

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Raspberry PI I/O expansion based on Gertboard

Walter Lain

This project was born because I wasn't able to buy an original Gertboard from Element14. The problem was that the kit at Element14 kept going out of availability, and also that Element14 won't sell anything in Italy to anyone without a VAT code.

While I was copying the schematic, it came to me that maybe I could make it more suitable to my needs. So, while it started as a perfect clone of the Gertboard, it came out with quite a bit of improvements (at least IMHO).

The specifications are thus the same of the Gertboard, with these differences:

The board is sized exactly to 150x100mm, since this is a price boundary for the small batch PCB manufacturers (such as Itead or Seed).

All the files needed for production are already packed in this zip file, so if you wish you can simply download it and put it on production.
This is the full BOM with the order codes for Mouser, with the right quantities to make 1 board (or as close as possible).
Finally, this is the spreadsheet to calculate the values for the Aux power circuit, should you want to change something.

Kicad project (you will need some libraries from here)

Test software adapted from the gertboard suite. This software will check your PI revision in order to address the right IOs. As for the gertboard version, it doesn't do anything really useful, it is meant to be used only to test the assembled board for any problem and as a start to write more useful programs to command the board or specific circuits based on some of its parts. With the revision 2 of the board, the software has been modified to make it compatible with the Raspberry Pi 2. Read the README file inside the zip file for further informations.

PDF documents
Back copper layer
Front copper layer
Front silkscreen
Drill map
Component versioning

The board can be used in any way while inside the boundaries of the CC-BY-NC-SA license. However, I'd advise you to give it a careful check if you plan to use it for anything else than an hobbyist testboard. I've made some tests with it, but certainly not enough for a full product qualification.

Please don't ask me if I can sell kits or parts or anything else. The answer is that it would not be convenient for you, since I'd have to ask for more than 200€ for each assembled board given the assembly time needed and components price. If you want an already made board or a prepackaged kit then go to Element14 and buy the Gertboard, or else ask someone you know to make it for you, or choose one of the other expansion boards available for the PI.

I've tested the switcher circuitry with a Vin from 8Vdc to 24Vdc, and I've been able to reach about 21V on the Vx pins with 24V on input terminal block. With Vout=12V and a load of about 1.1A for 24h, the AAVID 5772 heatsink stays under 70°C with a room temperature of 19°C (I've put thermal grease between heatsink and slug). This means that the system should be able to drive more than 15W without the need for a bigger heatsink.
Also, the line regulation is quite good, with the no-load output being about 12.027V and the 1.1A load output being about 11.975V.

Impaginazione by KCS'81