How does the sun-a-wear sensor work
The sun-a-wear sensor is a solar-powered device that measures UV radiation and sends these measurements wirelessly to the smartphone app. It stores the energy of the solar cell in a very small super capacitor. For the sake of simplicity, we will call this energy storage device from now on. This energy storage can only store around a millionth of your smartphone battery. This means that for the sun-a-wear sensor to work, it has only extremely little energy available and must therefore use it sparingly.
But how exactly does he do it? How does the sun-a-wear sensor work? What exactly happens when you take the sensor in the sun?
The switched off phase
If you have just received the new sensor or have not used it for a while, its energy storage is empty. He's turned off. If sunlight falls on the solar cell during this phase, a small chip on the sensor switches on: the Energy harvester (Eng .: energy harvesters). While all other components are still switched off, the Energy harvester that the solar cell charges the energy storage. It continuously adapts to the lighting situation in order to make ideal use of the energy supplied by the solar cell. Charging the energy storage device can take from a few seconds (in direct sunlight) to a few minutes (in the shade). When the energy store is about 2/3 full, it switches on the remaining components of the sensor. The important thing is the microprocessor that takes over the command from this point on. The sun-a-wear sensor changes to the measuring phase.
How does the sun-a-wear sensor work in the measuring phase?
When the sun-a-wear sensor has just come out of the switched-off phase, the microprocessor must first start the system. This means that he sets up the system and checks whether all components are there and working. Although this start process only takes about 6 milliseconds, it needs so much energy that the sensor goes to sleep again immediately afterwards. By “sleep” we mean that the microprocessor goes into a mode in which it uses very little energy. The system does not have to set itself up again when he wakes up. It can continue there, it can go on before going to sleep. Did you know that processors set an alarm clock to wake up at the right moment?
So when the sensor wakes up, it first measures how full the energy store is. When the memory is sufficiently full, it takes a measurement and sends it to your smartphone via Bluetooth Low Energy. Then he sets an alarm clock for 5 seconds and goes back to sleep. A short break.
So you can see that the measurement frequency depends on how quickly the sensor can fill its energy storage. In direct sunlight, it easily measures every 5 seconds. It can take longer in the evening.
If you take the sensor inside or it gets dark, the solar cell will no longer get enough light to charge the memory. Then the sensor measures and sends another two to three minutes and uses up a large part of the stored energy. Before the memory is completely empty, it goes into hibernation.
The hibernation phase
In the hibernation phase, the sensor does nothing but sleep. Well, every now and then he wakes up to see whether the energy store has filled up again. For example, it can survive longer phases in which you are indoors and does not have to restart the system over and over again.
But if it takes too long and he doesn't get any more energy, he will eventually go back to the switched-off phase and the game will start all over again.
As you can see, there is more going on behind the scenes than you think.
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