Designing a Low Power IoT Device for Electricity Price Monitoring
Aittola, Antti (2025)
2025
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Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:amk-2025092024906
https://urn.fi/URN:NBN:fi:amk-2025092024906
Tiivistelmä
This thesis presents the design and optimization of an ultra-low power IoT device displaying up-to-date electricity price in Finland on an e-paper display. The goal was to develop a compact device capable of operating for at least a year on a small battery.
The project began with the Soldered Inkplate 2 as the hardware platform. Testing revealed that its e-paper display’s slow 15 second refresh time was the main contributor to energy consumption. To address this, the hardware was changed to a Beetle ESP32 C3 microcontroller paired with a Waveshare 1.54-inch e-paper display and an external real-time clock (RTC) module. This reduced display refresh time to two seconds, significantly lowering energy usage.
Current profiling was conducted to measure energy consumption during first boot, hourly display updates, and once a day price data fetching over Wi-Fi connection. The Beetle ESP32 C3 achieved a deep-sleep current of 15.60 µA and daily consumption of 0.82 mAh, corresponding to an estimated battery life of nearly three years with current hourly pricing system. The upcoming shift to a 15-minutes electricity pricing period was considered, and the device still achieved an estimated battery life of over one year with its daily energy consumption of 2.06 mAh.
Future improvements could include reducing the physical size to a fridge-magnet form factor by designing a custom PCB and removing unnecessary components from the current development boards. Adding an indoor photovoltaic (PV) panel could in theory enable completely maintenance-free operation, but this would add device size, cost and complexity – especially in a battery-less design using a supercapacitor. Given that once-a-year charging is already effortless in a home environment, the benefit may be limited.
The project began with the Soldered Inkplate 2 as the hardware platform. Testing revealed that its e-paper display’s slow 15 second refresh time was the main contributor to energy consumption. To address this, the hardware was changed to a Beetle ESP32 C3 microcontroller paired with a Waveshare 1.54-inch e-paper display and an external real-time clock (RTC) module. This reduced display refresh time to two seconds, significantly lowering energy usage.
Current profiling was conducted to measure energy consumption during first boot, hourly display updates, and once a day price data fetching over Wi-Fi connection. The Beetle ESP32 C3 achieved a deep-sleep current of 15.60 µA and daily consumption of 0.82 mAh, corresponding to an estimated battery life of nearly three years with current hourly pricing system. The upcoming shift to a 15-minutes electricity pricing period was considered, and the device still achieved an estimated battery life of over one year with its daily energy consumption of 2.06 mAh.
Future improvements could include reducing the physical size to a fridge-magnet form factor by designing a custom PCB and removing unnecessary components from the current development boards. Adding an indoor photovoltaic (PV) panel could in theory enable completely maintenance-free operation, but this would add device size, cost and complexity – especially in a battery-less design using a supercapacitor. Given that once-a-year charging is already effortless in a home environment, the benefit may be limited.