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Introduction

A project log for NoiseCard

Solar-powered decibel measuring business card

clyneClyne 06/06/2024 at 00:120 Comments

The initial idea for this project spawned off of another that is using an ESP32 for continuous decibel monitoring. While the beefier ESP32 allows for wireless reporting of measurements, there's a price to pay in energy: 20mA or so of current consumption while recording from the I2S microphone, and a whopping 80mA while connecting to WiFi.

As a lover of ultra-low-power systems, I knew that microphone monitoring and decibel calculation could be done for a fraction of that energy budget. Searching for a viable low-power, low-pin-count microcontroller, I came up with the STM32G031J6: a tiny 8-pin SON package with a Cortex-M0+, I2S connectivity, and promising low power characteristics. I ordered its development board, the STM32G0316-DISCO, and began testing it with the microphone breakout board I had on hand.

Breadboard prototype
The MCU, mic breakout, and a serial monitor

After getting the system running with some code, it was clear that this could be very low power: down to 2mA at 1.8V -- less than 4mW! This was achieved through low clock speeds, optimizing calculations, and using an RTOS with sleep modes and interrupts.

Measuring current for the MCU + microphone

Now with the rise of Hackaday's business card challenge, I knew it would be no problem to stick these two ICs onto a PCB. With such little power required though, I wanted to push the limits and run the circuit entirely off of solar power; no bulky battery, just a thin, light card that could be used anywhere (where there's light).

So, the next step is to design a PCB...

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