February 18, 2026
Formal proofs, informal chaos
Show HN: Formally verified FPGA watchdog for AM broadcast in unmanned tunnels
Math‑proved tunnel radio sparks nerd fights, FCC jokes, and cave conspiracies
TLDR: A DIY system beams emergency AM messages through tunnels and uses a math‑proven safety timer to shut off if the app dies. Commenters split between praising the fail‑safe, debating audio tricks, and cracking FCC and time‑travel jokes—plus a wild detour into ancient caves—because the internet loves a side quest.
A hacker just dropped a 12‑channel AM emergency broadcaster for unmanned tunnels—with a hardware “watchdog” that kills the signal if the app freezes—and the crowd went delightfully feral. The creator claims the safety timer is mathematically proven (as in, proved by logic tools) to shut things down within five seconds. Cue the cheers…and the side‑eye. One commenter admitted they first thought “unmanned tunnels” was code for dodging radio cops, then pivoted to real use cases, linking to leaky feeder antennas used in mines. That set the tone: half safety‑engineering awe, half “is the FCC going to kick the door in?” jokes.
Radio tinkerers piled in with tweaks. The spiciest: phase‑shift or invert half the audio so broadcast peaks don’t all slam at once—translation: spread the loud bits so it sounds cleaner across many channels. Others begged for references. And then, as if on cue, a glorious derail about ancient stone sites and 72‑degree geometry appeared, proving that no matter how formal the proof, the internet remains extremely informal.
The mood? Big respect for a fail‑safe design that only restarts with a human hand, mixed with classic forum energy: regulatory paranoia, audio‑nerd optimization, and time‑warp humor. When someone crowned a commenter “winner of the Internet for February 18, 2006,” the thread fully embraced its destiny: serious engineering with a side of chaos, exactly how the hive likes it.
Key Points
- •12-channel AM broadcast system on Red Pitaya FPGA for emergency alerts in unmanned tunnels.
- •Runtime frequency configuration, AM modulation, dynamic power scaling, and stateless UI with device as source of truth.
- •Software uses Rust (Tauri) backend and JavaScript frontend with event-driven MVC and a defined state machine.
- •SCPI server converts frequencies to phase increments and writes to FPGA via /dev/mem; carriers span 505–1605 kHz.
- •Hardware watchdog (5s timeout) is formally verified with SymbiYosys + Z3, proving 14 safety properties and 6 cover scenarios.