Radish - Indoor Solar-powered Calendar Display

Austin Chau, Google Developer Programs
May 2008

You have probably heard of "20% projects" for Google engineers, which allows them to spend 20% of their time working on innovative projects of their choice. One of these projects is not only slick and creative but also environmentally responsible. Google engineer Aaron Spangler, from the Google Seattle office, often thought about how to reduce the paper consumption in Google offices. An idea came to him when he saw the amount of paper that is used on conference room doors to display room reservation schedules. Conference rooms at Google are managed within Google Calendar, allowing Google employees to schedule rooms via the Google Calendar interface. Room reservations are printed on pieces of paper which are then placed on the conference room doors each morning.

Aaron thought to himself, "If only there was a inexpensive device that could display the room reservations, we'll save all that paper ...."

That was the birth of the Radish project.

The goal of Radish is to replace this manual process with a portable device that can wirelessly retrieve and display scheduled events for conference rooms. For Google, this would translate to a savings of about six reams of paper a day, not to mention the printer resources and manual labor required to deliver the paper schedules to the conference room doors. Aaron has also determined that about 20-30% of all reservations are changed during the day, hence the Radish also overcomes the static nature of a paper display with real-time data.

The Radish is a working prototype that is built entirely from scratch and assembled using generic, off-the-shelf hardware components. Custom firmware was written in C and assembly language.

The CPU of the Radish board prototype is programmed to manage power usage and to transfer and display data. The display of the Radish is a special LCD screen that maintains the downloaded image without consuming power.

The Radish is equipped with radio transmitters that uses the IEEE 802.15.4 protocol to send and receive data wirelessly. IEEE 802.15.4 is ideal for ubiquitous communication between devices within a wireless personal area network because of its focus on delivering low-cost and low-speed communciation. This is why IEEE 802.15.4 is far more energy efficient (about 1mW per radio) than traditional Wi-Fi.

Radish uses the radio transmitters to ping and receive display data from an external server. This custom server fetches the set of event data pertaining to a conference room via the Google Calendar Data API. Using the Google Calendar Data API, the server is able to sync event data with Google Calendar. The event data is then processed into an image that is specifically sized for the LCD display. The MAC address of a Radish's wireless receiver is used as the unique identifier for the room it represents.

All electronic components were selected with one important criterion: that they must be compliant with the Restriction of Hazardous Substances (RoHS) Directive which restricts the use of hazardous materials (mainly lead) within electronic equipment. Another major area of environmental focus was the power supply of the Radish, particularly how to efficiently and cleanly power the Radish around the clock. The Radish team members (Aaron and fellow engineer Matthew Wilson) made a point of not using batteries to power the device. Instead, their desire was to utilize natural, carbon-free energy.

After investigating various energy sources, the team decided to use solar energy. Attached to the Radish board is a solar panel that collects and stores solar energy. The solar panel of the Radish is capable of collecting any source of light energy, including normal office lights, hence it might be more appropriate to say that Radish is powered by ambient energy.

The Radish is normally in an ultra-low power sleep mode. The Cholesteric LCD screen can maintain the final image state even in sleep mode, the state in which Radish spends most of its time only periodically waking up to ping its server for updates. The gap between sleeping and waking is determined algorithmically depending on how much energy it currently has in storage. With the ingenuity of the power management algorithm, the Radish is exceedingly efficient with power usage. A fully charged Radish can be running continuously for 3-4 days with a guarantee of at least one daily update, even in low light conditions.

The current plan is to trial deploy to a few Google offices, with the long term objective of eventually equipping all Google conference rooms with Radishes-yet another step closer to a paperless office.