Reverse-Engineering a Victorian Clock Tower's Mystery Microcontroller

When Portobello’s community trust Action Porty bought the town’s abandoned 1877 police station but couldn’t figure out how to set its three-faced clock tower, a couple of volunteers took on the puzzle. The original mechanism—likely as old as the building—had been retrofitted over the decades with electric motors and a control box. Setting the time turned out to be the easy part: they found a pawl that could be lifted to disengage the drive, letting them turn the hour shaft by hand (briefly panicking that the clock ran backwards before realizing they were viewing it from inside the tower).

The real head-scratcher was the chime. An unmarked, undocumented circuit board built around a PIC 16F628 microcontroller—date-coded around 2001—governs the striking mechanism, with relays, a lead-acid battery backup, and no real user interface beyond a cryptic ‘advance’ button. Through trial and error the volunteers reverse-engineered its logic: the box has no internal clock at all, just a counter driven by an hour-trigger switch on the main mechanism, with a striker switch counting chimes so it knows when to stop. Setting the hour means holding ‘advance’ until the count catches up, and a status LED blinks an as-yet-undeciphered code.

The piece is a small, satisfying study in field debugging of legacy embedded hardware with zero documentation—the same investigative instinct that drives a lot of security and reverse-engineering work, applied to a community restoration project. The clock now keeps time; the chime was deliberately disconnected to spare the neighbors, and the author is already sketching feature ideas like remote-triggered chimes and a doorbell that rings the bell.