YARH.IO M4

The M4 is where the YARH.IO handheld concept finally came together. Earlier builds proved that a pocket-sized Linux device was possible, but the Pi 4B is the first model that strikes the right balance between performance and power draw — fast enough to run a browser, an IDE, and background services simultaneously, yet efficient enough to deliver four to five hours of real use on a single charge. That runtime isn't a lab number with the screen dimmed and Wi-Fi off; it's actual working time with Chromium open, code compiling, and Bluetooth connected. The Pi 5 exists and it's faster, but this project deliberately uses the Pi 4B — its lower power consumption fits the form factor, the cooling, and the battery capacity in a way the Pi 5 simply can't match. A Pi 5 would drain the battery in under two hours and need active cooling that doesn't fit in a handheld shell. The Pi 4B is the sweet spot: powerful enough for real work, efficient enough to make a portable device that actually lasts. The result is a handheld that you reach for instead of a laptop — not because it replaces one, but because for most tasks it's all you need and it's already in your pocket.

At the core is a Raspberry Pi 4B with significantly more headroom than the 3B+ in earlier handhelds. The quad-core Cortex-A72 and up to 4GB of RAM make multitasking genuinely usable — you can run Chromium, VS Code, and a terminal session without the system grinding to a halt. A full aluminum heatsink sits on the SoC, and a GPIO-controlled fan on pin 4 kicks in at 60°C to manage thermals inside the enclosed case. A DS3231 real-time clock module keeps accurate time between boots, so the device doesn't need a network connection just to know what day it is. The display is a compact touchscreen panel that runs the full Raspberry Pi desktop stack, rotated and configured for handheld use.

The M4 runs i3 tiling window manager instead of the standard Raspberry Pi desktop — and on a small screen, this makes all the difference. A full desktop environment wastes pixels on panels, decorations, and a taskbar you don't need. i3 gives you the entire screen for your application, with windows tiling automatically and switching via keyboard shortcuts. The minimal X11 stack keeps memory usage low and startup fast. Custom keybindings are mapped to the keyboard's special keys: the Home key opens a terminal, the Mail key closes the focused window. Combined with dmenu for launching applications, the whole interface is keyboard-driven and surprisingly efficient once you learn the shortcuts.

The built-in Bluetooth keyboard connects via bluetoothctl and stays paired across reboots. The compact layout required some practical remapping — Caps Lock becomes Tab, which is far more useful on a device where you're constantly tab-completing in terminals and switching i3 focus. LightDM provides the login screen with custom YARH.IO branding, and the system boots directly into the i3 desktop. An external mechanical keyboard can be connected for extended typing sessions — the M4 is designed to work both as a self-contained handheld and as a desktop terminal when you need the full keyboard experience.

Battery monitoring is handled by dedicated hardware rather than guesswork. An LC709203F fuel gauge IC reads battery state over I2C — voltage, percentage, and charge rate — and a custom C++ service running as a systemd daemon writes the current readings to the filesystem. The i3status bar picks up this data and displays battery level right alongside CPU usage and network status. You always know exactly how much runtime you have left without opening a separate application. The monitoring firmware is straightforward to modify if you want to change the display format or add alerts at specific charge levels. And because the battery charges through a built-in USB-C charger module, you can plug in any modern USB-C power source — a wall adapter, a power bank, a laptop port — and the device will run indefinitely while keeping the battery topped off. Unplug it and you're back on battery without missing a beat.

The entire enclosure is 3D-printed and held together with machine screws — nothing glued, nothing snapped into place. The olive green colorway gives it a utilitarian, almost military look that's grown into a signature of this build. The adjustable stand lets you prop the device at different viewing angles on a desk, and the whole thing is compact enough to slip into a cargo pocket or a small bag. The software stack is tailored for development work: Chromium for browsing, VS Code and Arduino IDE for coding, Emacs with SLIME for Common Lisp development via SBCL, Samba for network file sharing, and minidlna for serving media to other devices on the network.