Less Is More When It Comes To Sensor Power

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.

Of course, you can do like the Matrix and harvest power from humans. It might not be as ridiculous as it sounds at first.

26 thoughts on “Less Is More When It Comes To Sensor Power

    1. Well, I don’t know what “ecosystem” means here, but, yeah, they talk about “accounts”, which means it’s apparently cloud dependent, which makes it a total non-starter. The only thing dumber than making your own house or facility dependent on somebody else’s cloud is making your *customers’* systems dependent on somebody else’s cloud.

      You also have to buy their gateway, but having their own RF protocol is more understandable.

      One hopes that $600 for two sensors and a gateway is a temporary thing to make sure limited early supplies only go to people who are serious about building something.

  1. the soviets once designed a bug which was powered by an externally transmitted carrier wave. it would then modulate that with the mic and transmit anything it picked up. i think had did an article on it once. anyway that’s the sort of vibe i get from this contraption.

    1. I recall a seminar (sorry, I am not finding the papers) showing off different RF devices for that. Different resonant circuits for temperature, soil moisture, even ones designed for structure monitoring (the circuit was printed on the surface so deformation/cracking would break the circuit and you wouldn’t get a reading)!

    2. Soviet bug used resonant receive, diode clipper to get 3rd harmonic, then audio modulated second chamber to send AM at 3rd harmonic frequency.
      Bugger to find because only had output when input was present.

  2. We are pumping so much RF energy into the atmosphere, e.g. cell towers and phones, WiFi, radio and television, satellite communications, radar; I would not be surprised that we could power some low power processors with sufficient antenna loops.
    But, as mentioned above, this cloud scam is a non-starter for me.

    1. We also generate a lot of heat – would be cool if there was Peltier cell for electric motor to power small transmitter with winding temperature data and or current consumption. This picture makes me think “why nobody thought about that before?”.

      1. Heat is not a problem, cool is. Thermoelectrics need one side hot and the other side cold, the greater the difference the greater the power. Heat is everywhere, but cooling the cold side is difficult, either you need a big heatsink and / or a fan that uses power.

      2. Because you have to aggressively cool the cold side. Thermoelectric generators (TEGs) can only output power as long as you maintain that temperature delta. As the heat goes through the TEG, both sides tend toward the same temperature, and the power output crashes. It’s hard to use them with continuous heat output unless you actively remove the heat from the cold side.

    2. https://www.freevolt.tech/

      I bought a device from this crowd on Kickstarter called a CleanSpace “Tag” (about the size of an iPhone SE) which contained a CO sensor as an Air Quality Sensor. It claimed to charge itself from stray WiFi energy.
      It connected to their own BT app in order to download the sensor logs.
      The device did work for a while (maybe 18 months) until the proprietary LiPo battery failed. I suspect the way it was delivering the charge didn’t suit the battery. Or maybe it just worked until the battery ran out of charge…

  3. How does this compare against say, EnOcean’s products? I thought the light switch that generates power through the mechanical switch action was clever.

    Both ST and Linear tech have had energy harvester parts for a few years for filling say a super cap, eventually enough to power a transmission that depletes the supercap then the process starts over.

    1. Have you every used EnOcean devices? I tried one that claimed to have a line of sight transmission distance of about 100 feet… I could get barely 10 feet within open air in an basic office environment. Although the concept is clever as you say, it has issues. Also, there are other companies offering mechanical to energy assemblies. OnSemi has a bluetooth (BT) device that uses one and it works not too bad all things considered. But the energy available limits the BT transmission content, etc. Sadly, the economies of scale have not increased enough to allow these mechanical energy generators to reach a price point to be mainstream.

  4. I kept an eye on research in this topic because it sounded good to have such sensor nodes.

    However, for indoor operation the energy harvester will not harvest as much energy as there is in a battery with the same volume over its lifetime of 10 years. Meaning: you are better of just equipping the sensor with a battery and replacing it after 10 years when it will be obsolete anyway.

    Things can change outside if you do solar or in special conditions where you artificially raise the ambient energy (RF/light) indoor. (i am including backscatter communication here too)

    1. Why would you assume the lifetime would be 10 years, or any specific number at all? I have a ton of possessions that are older than 10 years old and still work just fine. I have possessions that *100* years old and work fine. That might not only be longer than the lifetime of your battery, but longer than the lifetime of your battery’s chemistry or form factor, even if whatever dingus is accessible enough to let you change the battery.

      Not that I think these things will actually last that long, mind you.

      1. It’s a round number that sort of makes sense. It’s an ecosystem thag requires plenty of parts to be kept working, including software. The sensors will likely degrade. The tech will likely be obsolete in 10 years. You can push it to 15, maybe 20 years with special batteries.
        Sure, maybe some remote situation can need sensors to be fully independent for more than 10 years, but then we are talking about other requirements to extent the durability.

        All i say is, for majority of applications in harvesting indoor you can just use a battery that lasts the life of the sensor.

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