It used to be the cost of a microcontroller was a big inhibitor to putting brains in everything, but those days are long gone. Even 32-bit CPUs are now cheap enough that you can throw them into anything. The biggest factor now is probably power. Do you really want to charge your electric toilet seat or change batteries every few weeks? A company called Everactive wants you to ditch your battery using their sensor platform they claim harvests energy from a variety of sources and they are about to deliver their first developer’s kit.
The sensor can measure temperature, humidity, pressure, magnetic field, and acceleration on three axes. The device claims to harvest energy from radio frequencies, vibrations, small temperature differentials or light, even indoors. Our guess is that the sensor package runs on very little and when you poll the device wirelessly, the incoming radio signal supplies power for communication. The company claims its device uses 1000 times less power than competing solutions.
We aren’t sure if these claims are well founded or not, but we do agree that batteries are the bane of the embedded system. However, there are some cases — say a vending machine — where power is available and there are still other cases where you might not need a battery for low-power sensors, but you still need it for something else. For example, sensing a tank to turn on a heater, still needs power for the heater.
There are, though, other cases where having a self-powering sensor package will be just the ticket. We just don’t think it applies to every situation. We do like energy harvesting, but sometimes you can do a better job if you understand what you are building. For example, there are automatic flush valves that use the water flow to generate enough electricity to operate the device. If the energy storage device (like a rechargeable battery or a supercapacitor) gets low, you simply flush to recharge.