Back in 2019 we first came across the mutantC, an open source 3D printable Raspberry Pi handheld created by [rahmanshaber] that took more than a little inspiration from Sony’s VAIO ultra-mobile PCs (UMPCs) from the early 2000s. It was an impressive first effort, but it clearly had a long way to go before it could really be a practical mobile device.

Well after two years of development and three iterative versions of this Linux powered QWERTY slider, [rahmanshaber] is ready to show off the new and improved mutantC_v4. Outwardly it looks quite similar to the original version, with the notable addition of a tiny thumbstick and a pair of programmable buttons on the right side that can be used for input in addition to the touch screen. But inside it’s a whole other story, with so many changes and improvements that we hardly even know where to start.

Probably the most notable improvement is the addition of an ESP32-S2, specifically a bare ESP-12K module, to the main PCB. Previous versions of the hardware used an Arduino Pro Micro to interface with all the hardware, but the added horsepower of the ESP32 should come in handy with the array of sensors, controls, and NeoPixels that [rahmanshaber] has tasked the chip with. There’s even a buzzer and a coin-style vibration motor in there to provide some feedback to the user. While the board has changed significantly, it still retains compatibility with the Pi Zero, 2, 3, and 4.

Another notable addition is the expansion connector on the bottom of the handheld that has pins for I2C, UART, and 3.3 V. In the video below, [rahmanshaber] mentions that this feature was previously implemented with a standard 2×6 female header block, but is now using a far slimmer female USB-C port. We do wonder if it’s not a bit confusing to have this faux-USB port right next to the real one that’s actually used to charge the system, but with such cramped quarters occasionally you’ve got to make some tough decisions like that.

It’s quite inspiring to see how [rahmanshaber] has honed his skills since releasing the first version of the mutantC. The 3D printed parts and PCBs have matured considerably over the last two years, showing how quickly a dedicated hobbyist can advance their abilities. The most recent version has been entered in the 2021 Hackaday Prize. But the show isn’t over yet, as we hear v5 of this impressive handheld may tackle the Raspberry Pi 4 Compute Module.

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