Project | Solar powered Bluetooth Thermometer with Supercap | Hackaday.io

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Supercap vs. battery
04/16/2022 at 18:58 • 0 comments

One year runtime of two devices. Blue = with supercap, Orange = with CR2032 battery
The blue curve shows the daily charge / discharge of the supercapacitor.
The battery lasts approx. one year. and needs to be replaced by april 2022.
Small solar panel charging curve on 2 sunny days
02/25/2021 at 20:52 • 2 comments

The devices is placed on the balcony and charged with a small solar panel BR-243318C.

In direct sunlight the small version of the solar panel gives max. ~3.45V (- 0.3V of the Ge-Diode)

In ambient light the voltage is about 2.5V so the supercapacitor is not fully used .... this solution is suboptimal for indoor use.
24 MHz vs 48 MHz
02/25/2021 at 20:30 • 0 comments

I was curious what the impact would be on the overall power consumption. I plotted a comparsion between the voltage drop via 24 MHz & 48 MHz.

Seems that the 48MHz consumes less power as the device spends a larger part of the time in sleep mode.
Runtime test with 1.5F Supercapacitor
02/25/2021 at 20:12 • 0 comments

Voltage drop over time (mV / hours of day)
Charged 1.5F to 3.6V and let the thermometer run with 48MHz. Advertising interval 10s, measurement is done via plotting internal ADC values.
Below 2.0 V, the LCD is barely readable, but the Bluetooth transmission still works. This small voltage gap at around 2380mV seems to occure everytime, so something must drain power at this voltage.