Electronic Design

Apollo Would Approve Of This Self-Powered Wireless Sensor

The Sun God has been frowning on humanity for quite some time now as we continue to make little use of his gift that keeps giving—solar energy. But EnOcean Inc. gives him a reason to smile with its EVA120C wireless sensor kit, which relies on the company's STM110C solar-powered transmitter module (see the figure). Its small solar cell offers an integrated energy store for unrestricted functionality that lasts 60 hours in total darkness.

Using several of the kits, developers can construct a continuously adaptable wireless sensor network (WSN). A WSN built with STM110Cs can be used collaboratively to monitor temperature, gas, humidity, vapor, current, light levels, water, pressure, location, occupancy, and other parameters. WSN applications include environmental monitoring, home automation, and healthcare.

With the kit, engineers also can simulate performance, get results, and develop application-specific WSNs. It includes several data inputs, such as three 8-bit analog-to-digital converters and four digital inputs for detecting several types of conditions. To facilitate communication between multiple receivers, each kit includes a low-power radio transceiver with a 9-cm (868 MHz) or 24-cm (315 MHz) whip antenna.

Designers can set the kit's configurable wakeup signal via jumpers to alert the system every second or every 10 or 100 seconds. Upon wakeup, each unit broadcasts a telegram that includes its unique sensor ID, input data, and checksum. The computer monitoring the data from the radio nodes then would be able to detect any significant changes in input values compared to the last transmission.

In addition to the interval wakeup setting, the unit may be woken using a pair of pins. Any change in wakeup pin status will instantaneously wake the unit up. At that time, the unit will transmit all analog and digital inputs regardless of any change (or lack thereof) in the values.

The kit offers a transmission range of up to 300 m at a power of 10 mW. It can hit 125 kbits/s using amplitude-shift keying (ASK) modulation. Measuring 0.8 by 1.6 by 0.4 in., it includes RS232 and USB interfaces, a Microchip microcontroller, a low-power sleep timer, potentiometers to simulate analog inputs, an LED display to verify successful telegram transmission, and a threshold detector. The kit may be purchased for $530.

EnOcean Inc.

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