XIAC Museum — 2013 — Kopriso “Mi Esposita” Solar Nixie Watch (AU-2013)
An exploratory project focused on extreme efficiency: a fully solar-powered nixie wristwatch using a single-digit display, aggressive power management, and multi-purpose solar sensing.
The story
Mi Esposita (Spanish for “my little bride”) was not designed for production scale. It was built to answer a technical question: can a nixie tube wristwatch be powered entirely by light?
Achieving this required rethinking the display, power storage, sensing, and user interaction as a single system. The result was a watch that trades dual-digit familiarity for radical efficiency and brightness.
Model: AU-2013 • Year: 2013 • Brand: Kopriso
Documentation:
Original design and user documentation exists and is supplied with the watch. It is intentionally not published online, as Mi Esposita is a unique collector’s piece.
Design highlights
- Single-digit nixie display to minimise instantaneous current draw.
- Solar-powered operation with LiPo storage and protective charge logic.
- Multi-use solar panels: charging, ambient light sensing, and motion detection.
- Extreme efficiency HV drive with 512-step adaptive brightness.
- Trigger counter and battery reserve display for long-term behavioural insight.
Hero image
Mi Esposita (AU-2013). Single-digit B5853 nixie tube with solar panels beneath sapphire crystal.
Dutch heritage
A quiet nod to Dutch roots — personal history meeting exploratory engineering.
User expression
User-customised example. The core design allowed personalisation without altering electronics or structure.
Relationship to Cold War
Where the earlier Cold War watch explored dual-digit readability and symbolism, Mi Esposita explored efficiency, energy autonomy, and minimalism.
Same designer, same discipline — different constraints, different answers.
Cold War (AU-2012) — view pageDisplay brightness and drive capability
The Kopriso Mi Esposita Nixie watch was engineered to deliver an unusually high display brightness for a wearable device. At full output, the tube was driven beyond 4 mA anode current at approximately 180 V, placing it at the upper practical limit for Nixie tubes in a wristwatch form factor. Drawn battery current during operation is between 6.5mA and 200mA dependent on ambient light brightness and available battery power. Very easy on the eyes at night, while remaining clearly readable in daylight.
This same energy-aware drive strategy also enabled operation from a CR1216 button cell, dynamically adapting display current to the limited instantaneous energy available rather than relying on fixed drive levels.
Achieving this required a high-power, high efficiency, tightly controlled boost converter, careful thermal consideration, and strict duty-cycle management to ensure the display operated only in short, intentional bursts.
To date, this remains the brightest documented Nixie wristwatch display. A real-world brightness demonstration is available here: brightness test video .
Why the Kopriso Nixie watch was discontinued
Although the Kopriso Nixie watch proved that ultra-low-power electronics, solar charging, and high-voltage display technology could be successfully combined in a wearable form, real-world use highlighted a fundamental limitation: Nixie tubes were never designed for mobile equipment.
In practice, accidental drops occurred far more often than environmental issues such as moisture ingress. Even when the glass envelope survived an impact, internal metal structures could shift or shed microscopic particles, occasionally leading to cathode shorts or intermittent faults that were impossible to predict or economically repair.
In contrast to most modern nixie watches, which rely on USB charging and accept regular
recharge cycles, the Kopriso Mi Esposita solar powered Nixie watch was designed for near-zero maintenance —
capable of powering up after years of inactivity, with ambient light alone sufficient
to offset its ~3 µA standby current.
The Kopriso Nixie watches remain the only documented nixie
wristwatches capable of operating from a small CR1216 button cell — a result of
extreme efficiency-focused design.
Video proof of operation
.
Despite this, rather than continue producing a device where normal everyday handling could result in
costly repairs, the design was deliberately concluded as an exploration of the limits of
wearable electronics rather than a compromise in robustness.
Operating instructions
Original operating instructions for the Kopriso Nixie watches have been preserved and are provided here for reference. These documents describe the intended operation, configuration parameters, power-saving behaviour, and calibration features as shipped.
Note: Depending on the software release installed at the time of manufacture, some features described in these manuals may or may not be available.
These manuals are published for archival and support purposes and reflect the original design intent at the time of manufacture.
Related documentation
In 2026, a water-damaged Mi Esposita Nixie watch was repaired by its original designer — exactly 50 years after his first watch repair. The repair validates long-term design stability, energy-aware behaviour, and serviceability well beyond the original production period.