At $25 and $35 is Raspberry Pi is currently the cheapest board you can buy to develop for ARM Linux, however the expansion boards such as the Gertboard ($60) and the recent PiFace Digital ($32) are not as cheap considering the few components they have on board. This is why Olimex has designed a Raspberry Pi GPIO to breadboard & UEXT adapter (RPI-UEXT) which should be available in 2 weeks for 3.95 Euros (~$5). You then just need to add a breadboard for 2.95 Euros (~$3.8 ), which means for just $9 you can start prototyping easily with the Raspberry Pi.
The RPI-UEXT adapter (PCB Layout pictures on the right) also features – as the name implies – a UEXT (Universal EXTension) connector which consists of 10 pins which provide power (+3.3V/GND), and access to asynchronous serial I/O, I2C & SPI signals.
This connector allows to connect other UEXT modules manufactured by Olimex such as the MOD-IO2 board (12.95 Euros) which adds 2 relays and 7 GPIOs. There are currently over 20 UEXT modules whose prices range between 4.95 to 79.95 Euros (4.3″ LCD Module) including:
- 2x MOD-IO boards with relays, GPIO and analog inputs.
- MOD-RTC module that sells for just 4.95 Euros, so that you can easily add an RTC clock for about 9 Euros ($11.50) to the Raspberry Pi.
- 4 different LCD modules starting with a 1 row 9 character LCD to a 4.3″ LCD display.
- One RFID module
- 5 “connectivity” modules that provides Bluetooth, Zigbee, WiFi or Quad band GSM/GPRS
- One GPS module
- A Wii Nunchuck joystick with 2 buttons, a 3-axis accelerometer and XY joystick.
- 3 sensor modules – Accelerometer, magnetometer and temperature probe.
- One RS485 convertor module to control motor and/or other instruments.
- 2 “health/medical” modules for measure heartbeat and blood oxygen levels.
Other UEXT modules are also being developed such as an RGB LED controller, a 110/220VAC dimmer controller and an energy metering module. You can find more information about individual UEXT modules, including pictures, on Olimex post about RPI-UEXT adapter.