How to make a solar energy harvesting IoT sensor node?
Many applications that run on nano average powers can best make use of energy harvesting as their power source. Such applications include smart home, smart thermostats, smart locks, smart doors, smart windows, as well as the fitness bands and sports watches and activity trackers that we all wear. As well, hard-to-reach applications can really benefit from energy harvesting. Instead of sending out a technician every month or every year to change a battery, these applications can run without a battery and last forever.
Things such as implantable devices inside the human body or sensors on pipelines are good examples. Finally, environmental awareness, where the sensor is measuring the temperature, pressure, or humidity of a system and sending that information to a central host to make decisions about reliability, process variation, and so on.
Solar Dice: Solar-powered IoT sensor Node
A familiar energy harvesting application is solar. How can we harvest enough solar energy to power a particular load? Nano-power DC-DC converters are the solution.
Here we discuss the ‘Solar Dice’ reference design from TI that walks designers through a simple, flexible and cost-effective solution to power sensors and other ultra-low power devices that contain no batteries or very small capacity batteries.
This solar device, a wireless sensor node, in the IoT, has six solar panels, one on each side, and they’re connected in series to create a higher voltage. And whenever the dice is rolled, the onboard accelerometer wakes up. The orientation, which side is up, is transmitted to the host. As it’s usually not enough energy in the cells themselves to complete a task, so this energy is stored in a capacitor. Then a nano-power DC-DC converter, the 62740, creates the core rail needed for the CC430 radio. This radio has a built-in ADC (analog to digital converter) to sense the voltage of the solar panels. Now, this is important to make sure that we have enough energy stored in that capacitor to start up and perform the required tasks of the system.
The entire thing draws a couple microamps when it’s in standby. And this is due to ultra-low power-optimized power supply and ultra-low power-optimized code. The MCU has to be very intelligent about when it wakes up based on how much stored energy there is in that capacitor. And when it wakes up, it takes the measurement with the ADC and transmits that to the host before it runs out of energy.
This wireless sensor node can measure anything with this– temperature, pressure, humidity, and so on. All the design files are found on the reference design page, PMP 9754.
- Battery-less operation from 6 solar panels
- Orientation wirelessly transmitted to host
- 2.36 µA current draw (standby mode)
- Ultra-low power optimized power supply
- Ultra-low power optimized code
For more information on the design, click here.