If you’re pairing a tiny Linux computer to a few peripherals — perhaps you’re building a reasonably custom Pi-powered device — it’s rightfully tempting to use something like an STM32 for all your low-level tasks, from power management to reading keyboard events.

Now, in case you were wondering how to tie the two together, consider HID over I2C, it’s a standardized protocol with wide software and peripheral support, easily implementable and low-power. What’s more, [benedekkupper] gives you an example STM32 project with a detailed explanation on how you too can benefit from the protocol.

https://github.com/benedekkupper/stm32-i2c-hid/

STMicro Unveils the Entry-Level STM32U0, Drawing as Little as Half the Power of Its Predecessors
Designed to deliver up to twice the battery life of last-generation alternatives, the STM32U0 family has a single 56MHz Arm Cortex-M0+ core.

https://www.hackster.io/news/stmicro-unveils-the-entry-level-stm32u0-drawing-as-little-as-half-the-power-of-its-predecessors-75b80cb0a290?fbclid=IwAR1y2ogOTlxOo-eDBE265QV84q3eFODKUwl3pV0qRl1t4mNSfMTNqwSomc0

The recommended STM32G431 is a wonderful tool for the task in particular. For a start, this board exposes nine 16-bit ADC inputs, with six of them capable of differential mode and three of them having the PGA (Programmable Gain Amplifier) feature. There’s also two 12-bit DAC pins, two timer outputs, three GPIOs, and UART with I2C for the dessert. As a bonus, it can work as a PD trigger, giving you higher-than-5V voltages out of USB-C for any experiments of yours.

https://github.com/Jana-Marie/analog-toolkit

If you’ve scavenged some random keypads and want to reuse them in a project without the hassle of figuring out the pinouts, then [Cliff Biffle] has an interface module for you. The Keypad Go connects to the mystery keypad via an 8-pin 0.1 inch header, and talks to your own project using I2C and/or serial.

You could categorize the mechanism at work as machine learning of a sort, though it’s stretching definitions a bit, as there is no ChatGPT or GitHub Copilot wizardry going on here. But you must teach the module during an initial calibration sequence, assigning a 7-bit ASCII character to each key as you press it. Once trained, it responds to key presses by sending the pre-assigned character over the interface. Likewise, key releases send the same character but with the 8th bit set.

The heart of the board is either an STM32G030 or STM32C011/31, depending on parts availability we presume. I2C connectivity is over a four-pin STEMMA connector, and logic-level serial UART data is over a four-pin 0.1 inch pin header.

https://cliffle.com/widget/keypad-go-1/