Typical sensor nodes have an explicit “sensor chip” on board that is sampled at runtime and the reading is reported back to a collection server. The nodes are usually powered by a battery and aggressively duty cycled. This project takes a very different approach to how sensor nodes are designed. Here, we replace the battery with an energy-harvesting power supply. Then, we use the insight that the rate at which the energy-harvesting power supply can successfully power the sensing node tells us something about the power source. That is, the energy-harvesting power supply is the sensor.
We use this principle to build a power meter. The energy-harvesting source is the electromagnetic field generated by the current flowing to a load. Using a current transformer we harvest from this source to intermittently power the node core. When the node activates it transmits a packet to a central receiver. The receiver can then determine the power of the attached load based on the frequency of packets from the Coilcube node.
The coilcube platform works well for plug loads and for measuring entire circuits in a circuit panel. Loads like installed lighting are hard to measure with the AC power meter. To compensate, we have an indoor solar energy-harvesting power supply that operates with the same principle. When installed near a light the rate of activations is proportional to the brightness and power draw of the lighting.
- Monjolo: An Energy-Harvesting Energy Meter Architecture
SenSys '13 (Embedded Networked Sensor Systems)