Lots of development boards can easily fit into your pocket. In fact, a majority of them are so small that you could easily forget you are even carrying them. However, the compact design of these boards can be deceiving. Unless you happen to also be carrying around a laptop loaded with an appropriate software development toolchain, that board isn’t actually of much use for any real-world applications, like hardware debugging.
DevPocket is a compact, battery-powered debugging and prototyping device that was designed for use in the field — no PC required. It comes equipped with a MagSafe-compatible magnetic ring so that it can attach to a compatible phone. When connected to a phone’s USB-C port, DevPocket immediately becomes available for use with apps such as Micro REPL, which allow you to code and run scripts without any additional hardware or complex software packages.
Another look at the hardware (📷: Ilya Egorov)
DevPocket is designed around an ESP32-WROOM-32UE microcontroller, offering both Wi-Fi and Bluetooth connectivity, paired with a CP2102 USB-to-UART bridge for communication with mobile devices. A built-in 900 mAh LiPo battery, charged via USB-C, keeps the system portable, while onboard power regulation ensures stable 5V and 3.3V rails. The inclusion of addressable RGB LEDs and configurable tactile buttons adds immediate user interaction without requiring external components.
Unlike typical microcontroller boards, DevPocket makes use of a full-size mPCIe slot as a universal expansion interface. Rather than limiting users to pre-defined modules, the slot exposes UART, SPI, I2C, GPIO, and selectable power rails, enabling fully custom hardware add-ons. This approach effectively turns the device into a modular ecosystem, where users can design plug-in boards for sensors, displays, or communication modules.
One of the first such modules developed for DevPocket is an environmental sensing board designed to monitor air quality. Built in a compact mPCIe form factor, it combines three sensors on a shared I2C bus: a BMP280 for pressure and temperature, an AHT20 for humidity, and an ENS160 for air quality metrics such as eCOâ‚‚ and TVOC levels. Careful power design, including dedicated low-dropout regulators, ensures stable operation even with mixed-voltage requirements. Early testing confirmed that all sensors were correctly detected using a simple I2C scanning script executed directly from a smartphone.
The device can be programmed and managed from a phone (📷: Ilya Egorov)
Developers can write and execute MicroPython scripts directly from their phone, with no reliance on a desktop environment. A simple launcher interface controlled by two onboard buttons allows users to scroll through stored scripts, execute them, or place the device into deep sleep for power conservation.
As an open source project, DevPocket invites further experimentation and customization. If you’d like to get in on the action for yourself, be sure to take a look at the full project write-up.
