Sunday, July 1, 2012

Wireless Gateway for Raspberry Pi

Wireless gateway for Raspberry Pi
Wireless gateway for Raspberry Pi. Click on the image for an annotated version.

Introduction

A wireless gateway for the Raspberry Pi is presented. The gateway will connect remote clients to the Raspberry Pi and the internet. I plan to use these to connect a network of magnetometer sensors to improve the reliability and availability of the AuroraWatch UK network. The gateway can also be used to program Atmel AVR microcontrollers, as used in the magnetometer sensors.

Design Goals

  • Footprint for XBee, Ciseco XRF, or similar radio module.
  • Footprint for Hope RFM12B radio module.
  • AVR ISP programming header.
  • Maximum board size 50 mm × 50 mm (to use cheapest Iteadstudio PCB fabrication option).
  • All unused digital I/O brought out to pads for easier extension, prototyping and hacking.
It is intended that all hardware directly interfacing with the gateway will use 3.3 V signal levels.

Features

The board has footprints for both RFM12B and XBee (or similar, such as the Ciseco XRF) radio modules and since they use different interfaces and GPIOs both can be used simultaneously. There is an FTDI connector to the Raspberry Pi's UART; this is shared with the XBee so both cannot be fitted at the same time. Only the minimum required set of digtal I/Os for each module have been hard wired. The RFM12B /CS input and /IRQ, and XBee /RESET, can be connected via jumpers. The remaining digital I/Os from the RFM12B, XBee and even the FTDI connector can be used by adding link wires to the desired Raspberry Pi's GPIOs on the second header footprint. If not needed then a pin header can be fitted to allow another expansion board to be stacked on top of the wireless gateway. The maximum current draw from the P1 connector's 3V3 pin is 50 mA. To enable higher power radio modules to be used the wireless gateway includes a built-in 3.3 V voltage regulator (250 mA limit)

Connecting to the gateway

To connect to the Raspberry Pi wireless gateway you might also be interested in Calunium, my shield-compatible Arduino clone based on the ATmega1284P. The latest version will include space for an RFM12B radio module.

Build it

At the moment the design is preliminary and untested. Eagle PCB design files are available under the Creative Commons Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0) licence. The files will be updated as the design progresses.

Warning!

The Wireless Gateway for Raspberry Pi is intended to be used with 3.3 V devices only. Using it with 5 V devices (e.g., Arduino) will very likely damage your Raspberry Pi.

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