Hobbyist refines analog voltmeter clock with precision microcontroller and custom woodwork

A hobbyist has documented the construction of a revised analog voltmeter clock, a project that blends embedded systems engineering with traditional woodworking techniques. The design features three 90-degree panel meters capable of continuous hand motion, replacing the discrete ticking found in many previous iterations. The mechanism is driven by an AVR128DB28 microcontroller, which utilises a high-frequency digital pulse train to control meter inertia, allowing for smooth, intermediate positioning of the hands.

The hardware is integrated into a custom enclosure that required significant fabrication effort. The front and back faces were cut using a CNC mill to accommodate a recessed decorative pattern, a design choice made to conceal the plastic flanges of the generic panel meters. The side wall presents a more complex challenge, constructed from a flat piece of wood that was moistened, notched internally to allow flexibility, and then steam-bent around a shaped template. After drying and gluing, the assembly was finished with sanding and a coat of nitrocellulose lacquer.

At the core of the circuit is the AVR128DB28 microcontroller, powered by a standard wall adapter and synchronised with an 8 MHz crystal oscillator. The system interfaces with three digital output pins to drive the meters and utilises two input pins connected to pushbuttons on the rear panel for time setting. Notably, the design eschews digital-to-analog converters or additional driver components. Instead, the software controls the duty cycle of the digital signal, relying on the physical inertia of the meter movements to settle the hands at the correct positions.

The software logic is straightforward, advancing a 10 Hz counter via a timer interrupt. The main event loop calculates the necessary duty cycle for each meter and manually toggles the output pins. Although the microcontroller possesses a hardware pulse-width modulation module, the developer determined that the application’s simplicity meant that using the dedicated hardware would not provide significant advantages over the manual toggling approach.

This project represents an evolution of a design first built in 2019. The original iteration was kept on an office desk, but the developer noted that most existing internet designs for this concept were overly complicated and aesthetically lacking. The revised version addresses these concerns by streamlining the circuitry and focusing on a cleaner, more refined aesthetic through the use of precision manufacturing and careful material selection.

The complete code for the project is available for review, described as short and well-commented. The build documentation includes printable PDF templates for the meter faces, with the hour gauge featuring 13 divisions and the minute and second gauges featuring 61 divisions to support the continuous motion logic. The project highlights how basic digital signals can be manipulated to achieve analog-like smoothness through careful software control and mechanical design.