Pip-Boy 3000 Geiger/GNSS Mod Board
The module is designed as an instrumentable engineering platform: the high-voltage supply, pulse chain, counter, GNSS timing, and host stream can each be measured independently before the system is trusted.
Problem and constraints
The miniature SBM-21 enables a compact assembly but has low sensitivity, requires approximately 400 V bias, and produces statistically noisy low-rate readings. Fitting its switching supply, ESP32-S3, GNSS antenna, pulse chain, service port, and host interconnect into a 60 × 30 mm Pip-Boy cavity adds mechanical and RF-coexistence constraints that the board cannot hide.
Engineering approachArchitecture and implementation
An ESP32-S3 regulates a PWM boost and voltage doubler through monitored feedback, while a cathode pickoff and fast comparator produce one clean hardware-counter edge per tube event. A dedicated GNSS UART plus 1PPS supplies position and time, and the firmware emits one checksummed fused reading per second over USB-C, TTL UART, Wi-Fi, or BLE.
Signal chain
The tube pulse passes through a cathode pickoff, AC shaping, clamp, and TLV3201 comparator before reaching the ESP32 hardware pulse counter.
Data contract
Counts, smoothed dose estimate, high-voltage state, coordinates, altitude, fix quality, satellites, and UTC are combined in an NMEA-style $GM sentence.
Boundary
The design is for engineering and educational use. Prototype calibration, high-voltage insulation, enclosure safety, and RF testing remain open; it is not a safety dosimeter.
Work in progress.
Design and implementation records remain private while this work is in development.
Private development record
Design notes and implementation records are not public while this work is in development.