$5 Add-on Board for Raspberry Pi Supports Arduino Shields and Grove Modules (with Caveats)
If you have several Arduino shields, you can use them on your Raspberry Pi B+/ Pi 2 board with Cooking Hacks’ Raspberry Pi to Arduino shields connection bridge supported by arduPi library to control I2C, SPI, GPIO, analog inputs, etc.., and sells for $65 on Amazon. Seeed Studio Grove modules have also become more popular, with several new boards integrating 4-pin Grove connectors such as Beaglebone Green. Raspberry Pi boards also support Grove modules, up to 15 of these!, using Grove Pi+ add-on board which the company sells for around $30.
But I’ve just discovered a Raspberry Pi to Arduino Expansion Board V2.0 on DealExtreme, selling for $7.97 that’s allows the latest Raspberry Pi boards with a 40-pin headers to take both Arduino shields and 2 Grove modules. After some investigations, I found out it was made by ITead Studio, where they sell it for $5 + shipping. The Wiki does provide some more information, and reveals the limitation of this add-on board.
The schematics above shows no conversion is done, and while Raspberry Pi I/Os support 3.3V, many Arduino shields can only work with 5V I/Os, so you may to add your own voltage conversion which negate the advantage of such board.. Arduino shields with analog inputs won’t be usable either. The few Grove modules I’ve checked support both 3.3V and 5V, so the situation is better here, and the add-on board also has a 3.3V or 5V selector for VDD.