Bhangmeter V3 — The Optical Detector
Where Bhangmeter V2 catches the invisible gamma-ray flash, V3 watches for something you could almost see with your own eyes: the double flash of light that every nuclear fireball produces. And it can do something the gamma detector can’t — estimate the yield.
The double flash
Every nuclear fireball flashes twice. The first flash is a brief, blindingly bright pulse lasting about a millisecond. The growing shockwave then briefly cloaks the fireball, dimming it to a momentary minimum — before it bursts back into a second, longer and even brighter flash. This double flash is so distinctive that it’s how satellites have spotted nuclear tests for decades.
Nothing else in the sky does this. Lightning, camera flashes, strobes and meteors all flash once, or flicker unevenly — so V3’s detector is built to ignore them and hold out for the one signature that matters.
Reading the yield
The clever part is that the gap between the two flashes grows with the size of the bomb. Measure that interval and you can work backwards to an estimate in kilotons — from around 10 kt all the way up to a megaton, for a blast tens of kilometres away.
V3 records two timings: the peak-to-minimum time as a quick cross-check, and the peak-to-peak time as the main yield estimate. Both feed straight into the live readout on the home page.
What’s inside
V3 turns the light curve into numbers with a purpose-built optical front end:
- A VEMD2704 photodiode senses light across the visible and near-infrared band, where the fireball is brightest.
- A logarithmic amplifier squeezes an enormous range of brightness — roughly seven decades — into one fixed-gain circuit, so it never has to switch gears mid-flash.
- A fast comparator marks the exact moment of each peak, and an ADC captures the shape of the waveform.
- An RP2350 (Pico 2 W) runs the detection algorithm on the spot, times the flashes, computes the yield, and publishes the event over WiFi.
Build one yourself
Bhangmeter V3 is fully open-source — firmware, host software, PCB schematics and 3D-printable enclosures are all published. Full details are on GitHub: Bhangmeter V3 — optical detector.