Energy harvesting meets Raspberry Pi

Front_of_Raspberry_PiAt first glance the Raspberry Pi looks like a simple programming board, not bigger than a credit card, with some ports. At second glance, it is exactly what it looks like.

But this very simplicity resulted in an unparalleled success with approximately 1,000,000 boards sold in the first year. If each Pi is stacked end-to-end, it would reach the length of 10,140 double-decker buses.

The Pi’s special feature is its combined flexibility and performance. Due to its many ports, it can connect to a large number of external devices used in our daily life, such as USB peripherals, HDMI for TVs or monitors, SD memory cards, Ethernet for all Internet-based connections or audio and video streaming. And it fits in a pocket.

A strong community of electronic and computing enthusiasts develop several Pi-based applications. One of these is home automation.

With its multi-connectivity and powerful processing options, the Raspberry Pi is the perfect platform for a low-cost smart home gateway which controls energy harvesting wireless sensors. This can be realised in a few steps.

Batteryless sensors and switches are ideal to get started with home automation. The devices are powered by an electro-dynamic energy converter which uses mechanical motion, or a miniaturised solar module which generates energy from light. Combining a thermoelectric converter with a DC/DC converter taps heat as an energy source. The radio protocol uses sub 1 GHz frequency bands, wireless signals are just 0.7 milliseconds in duration and are transmitted multiple times for redundancy.

To transform the Raspberry Pi into a smart home server integrating energy harvesting wireless solutions, the following accessories are needed: power supply (~1A) with micro USB plug, HDMI cable, SD card (e.g. 4GB), Ethernet cable or USB WLAN stick and an EnOcean Pi board. As a first step, Raspian wheezy image (Debian Linux for Raspberry Pi) needs to be installed on the SD card.

This is available for download at the raspberrypi.org website. After plugging the SD card to the Pi board and its configuration, EnOcean Pi needs to be connected on the Raspberry Pi’s top.

As default, the serial port of the GPIO interface is used for console debug outputs. In order to use this port for EnOcean Pi, this feature has to be disabled first. In a next step, the connection can be tested with raw data from EnOcean Pi by using hexdump.

For this, EnOcean Pi provides a serial stream of EnOcean radio telegrams according to ESP3 protocol (EnOcean Serial Protocol 3.0). The protocol describes the serial communication between a host and energy harvesting wireless receivers.

For remote control via TTY (e.g. PuTTY) or HTML server connections, the IP address of Raspberry Pi is needed. Users can get the allocated IP address (e.g. by DHCP server) by typing in the command: “ifconfig”. After this, developers can start with the installation of a building automation server based on GPL software (General Public License) such as FHEM or openHAB. Instructions can be found on the according websites.

The EnOcean Pi accessory is supplied with free to download EnOcean Link Trial version middleware. It decodes and encodes data communication according to the EnOcean profile standard and executes device connection. The trial version offers a selection of application profiles as well as instructions, for testing the basic functionality of the software.

With these components, users now can start to use the Raspberry Pi-based home automation server to automate common tasks like switching lamps, scene illuminations or pulling blinds, measure and visualise power consumption, temperature and humidity.

EnOcean Pi serves as a gateway controller to batteryless wireless applications. This could be a solar-powered radio sensor (e.g. STM 330 temperature sensor or STM 320 reed contact sensor) which periodically sends values to be interpreted and displayed via the web interface. With the duo of Raspberry Pi and EnOcean Pi, developers can open up the world to energy harvesting wireless control in a few steps.
Laurent Giai-Miniet, CEO, EnOcean

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