ENTtinymachines

The bench

The pool is what hotbits serves; this is the bench it comes from. A Geiger tube counts in a steel case on its own supply, an optocoupler carries each count across as light, and an ESP32-C6 outside the case times every edge in hardware before the server turns the gaps between them into bits. The bring-up was done the way the NES bench was: a scope driven from a script, the board flashed from the bench, and every step written down.

These are revision F of the drawings. Nothing on the sheets is marked not confirmed any more: the counter is alone on the chassis supply, the emitter is on its own brick outside the box, and the detector and the optocoupler are sealed in a container inside the chassis. The one thing still unread is whether the chassis is bonded to a ground.

The Geiger TRNG as three places: the case with the counter and its tube, the emitter outside it, and the server, with what crosses between them.
Three places and what crosses between them: only light crosses the case's isolation barrier, only a TCP stream leaves the emitter, and only the web server is public.
Sheet 3 of the drawing package: the counter board's connector pin by pin, alone on the chassis supply's 5 V line, and the optocoupler's LED between the connector's 5 V pin and the detector transistor's collector.
The case, drawn pin by pin: the counter board alone on the chassis supply's 5 V line, nothing shared with the emitter, and the optocoupler's LED tapped at the detector transistor's collector, where a count can light it.
The emitter: one capture pin, GPIO18, on an ESP32-C6 board, with the lead from the case and its pull-up.
The emitter, outside the case on its own USB power: one pin latches the counter on each falling edge.
The signal chain from the tube to the capture pin, with the three places a probe goes.
Where to put the probe, one hop at a time from the source toward the pin.

The whole package, every sheet framed and numbered: Geiger TRNG emitter: the detector and an ESP32-C6 in a box: drawing package TM-TRNG-001 rev F (PDF)

What the instrument is

How a decay becomes a byte: the counter, the bits, the tests that refuse to serve, and the gateway in front.

  • The instrument: A Geiger counter whose every count is timed in hardware, and the chain from a decay event to a byte somebody can fetch.
  • The bits: One bit per pair of gaps, with the bias cancelled by symmetry rather than by correction.
  • The health tests: Three layers on three timescales, and the one that refuses to serve.
  • The gateway: Why the open endpoints closed, what stayed open, and what a browser is allowed to see.

Building the bench

The emitter as drawn and as built: the drawings, the boards, the parts, and which ESP32 does which job.

  • Which ESP32 does which job in the NES notebook: Which Espressif chips can be a Bluetooth keyboard, which a USB one and which both, read from the vendor's own headers for eight of them rather than remembered; the comparison that moved the pad onto a P4 module.

Experiments at the bench

The scope on the signal chain, what the counter's own timing costs in counts, and how the source's quality is tracked.

  • Using an oscilloscope, for software developers in the NES notebook: A scope as a debugger for the wire, taught on a real fault: a Geiger counter that clicked while its firmware counted nothing. The ground clip, the trigger as a breakpoint, bisecting a signal chain, scripting the scope over SCPI, and the ways the instrument itself was wrong.