Light-powered wireless sensor module works indoors

A Siemens spinoff called EnOcean has developed a light-powered wireless sensor module which can transmit signals from analogue or digital sensors, powered by typical indoor light levels. The STM100 module stores enough energy onboard to operate for five days in complete darkness. It eliminates the need for batteries and thus for regular maintenance.

The 2 x 4 x 1cm module (above) uses a two-stage solar cell. The first stage provides quick start-up energy, while the second charges up the on-board energy store. It needs just 200 lux to operate - a typical value for a building hallway.

"With just 50µW, a standard EnOcean transmitter will comfortably send a signal 300m outdoors, or 30m indoors through walls," says Armin Enders, the company`s vice-president for product marketing. "The secret is in the signal duration - the entire process is initiated, undertaken and completed is approximately 1/1,000 of a second."

The module provides three analogue and four digital inputs and can support a variety of sensors. It costs less than $25 in OEM quantities.