Dhruv Wadhwa's Eight-Bit Handheld Is a Raspberry Pi Pico-Powered Retro Throwback

Self-confessed "electronics nerd" Dhruv Wadhwa has designed a handheld computer on a prototyping board, powered by a Raspberry Pi Pico and offering a retro bit-by-bit programming process inspired by front-panel systems like the Altair 8800.

"[It's] an eight-bit handheld computer emulator inspired from Ben Eater's breadboard computer and [the MOS Technology] 6502 processor," Wadhwa explains of his creation, which owes much to the very first days of personal computing. "The handheld computer incorporates the Raspberry Pi Pico as well as push buttons, an OLED screen, and an IMU [Inertial Measurement Unit]."

While today most computers are programmed in high-level languages, written comfortably with a keyboard in a feature-packed Integrated Development Environment (IDE), that wasn't always the case. Early computers were laboriously programmed bit-by-bit, literally, by stepping through the memory and flipping front-panel toggle switches to change zeroes to ones or vice-versa.

That's exactly how Wadwha's unnamed creation is programmed — albeit using push-buttons and in a far more compact, pocketable form. "It has two modes: PROG mode and RUN mode," Wadhwa explains. "In program mode, you may travel through all of the RAM regions and edit their contents, allowing you to program it. The run mode displays the values of different CPU modules such as A and B registers, program counters, flag registers, and so on. It has a clock and a reset button. Pressing the clock button once single-steps the computer, and keeping it down runs the clock indefinitely."

One tip to modernity, aside from using the Raspberry Pi Pico and its RP2040 microcontroller to emulate a simple eight-bit processor and its peripherals, is the display. As well as showing the current memory location and its contents, in place of the LEDs or lamps traditionally used, it updates constantly in run mode — providing a glimpse at exactly what the processor is doing.

More information on the project is available on Wadhwa's Hackaday page, while an emulation of the emulator is available on Wokwi for interactive use. The source code, meanwhile, has been published to GitHub under an unspecified open source license.