low power sensors
Utilising Atmel's picoPower low power technology with an AVR ATXMEGA128D3 we have been able to design and build a powerful wireless sensor capable of measuring and processing a range of different parameters whilst running from a single 3.6V lithium battery for over a year between battery servicing.
The processors sleep mode is the key to this technology, allowing the core and peripheral clocks to be halted whilst the device is asleep with the exception of an ultra low-power 32kHz watch crystal which wakes the device up several times in a second for very short period of time. During this short wake-up the processor can still maintain any real-time counters / timers and check core I/O before either going back to sleep or triggering measurements to be taken before going back to sleep.
Another CPU feature exploited is the ability to change its core clock frequency. Unlike some processors the XMEGA can rapidly enable and switch between different clock sources, allowing for up to 32MHz performance during a data processing phase before dropping back to a much more sedate 8 or 10MHz clock during the measurement phase.
Due to the low currents required to run the various sensors, IO pins of the processor are used to power up and down sections of the board when needed so as not to waste power.
Typical average power consumption for the board is around 1uA with its highest current consumption around 40mA while transferring data via the RF module.
This sensor was our first device to be packaged in an entirely bespoke enclosure. Due to the way that the device needed to be attached in use and the space available for mounting it, using an off the shelf enclosure wasn't an option. Early prototypes were manufactured using an enclosure machined from solid plastic until the system operation was proved at which point our mechanical designer worked with a company in China to produce a moldable enclosure which took as expected a couple of iterations to tweak and perfect before 2000 production parts were manufactured.