A group of volunteers in Edinburgh devoted an entire Saturday to working out how to adjust the time on a clock tower at the old Portobello Police Station. The clock proved much more complex than anyone had anticipated.
Action Porty purchased the building for the community and requested assistance with the timing. A friend reached out with a note asking whether the writer would rather join him atop the dusty nineteenth-century clock tower than meet in Edinburgh. The writer eagerly accepted the invitation.
The building’s history
Built in 1877, the police station was originally designed to host meetings, administration and courts for Portobello burgh council. Once the town was folded into Edinburgh, it served as a library before returning to its former use as a police station. Funding from the Scottish Land Fund allowed the community to purchase it, and today volunteers are stripping away the 1970s polystyrene ceiling tiles and wood-chip wallpaper to uncover the building’s original splendor.
The clock’s internal works are probably from the original build, even if changes were made down the road. Modern electric motors drive the mechanism today, and a separate control unit lets the clock chime be switched off at night.
Climbing the ladder
The writer called it a climb up a steep, tall ladder into what was almost certainly spider-infested darkness. The payoff was an attic packed with steps that led straight to the clock tower.
The writer stepped inside and beheld the grand spectacle of the clock’s workings and its three faces. The initial task was determining how to set the time.
Setting the time
A small motor sends power through a set of gears to a shaft that turns once an hour. That shaft divides into three parts, one for each face, which moves the minute hand straight away. Each clock face gets its own gear to derive the hour hand.
One of the gears held a pawl that could be raised out of the way. After that was done, the shaft turned freely, and the time could be adjusted by picturing the unseen hand opposite each counterweight.
The clock seemed to be moving backward for a brief spell, which caused a wave of fear. Then the writer understood they were within the mechanism itself, viewing it from the wrong angle. A trip to the floor verified that the time was correct and the hands were not actually reversing.
The mystery box
The chime setting proved more difficult than expected. Someone had altered the original mechanism, adding switches and a motor to it. A box with a circuit board fitted with a PIC 16F628 microcontroller was found inside, bearing a presumed date-code of 2001. Relays, a power supply and a battery charging circuit for a lead-acid battery were also part of the assembly.
Nobody could say who created the box or put it together, and there was nothing on it to identify its maker. The writer wonders if it is a standard item or a custom piece made just for this clock.
Deciphering the interface
There was hardly any way to control the device on its surface. One button was labeled “advance,” though pressing it produced no effect at all. The writer found himself measuring, puzzling and experimenting until he finally figured out what it was meant to do.
A mains-powered motor runs the chime striker mechanism inside the box. That motor keeps the clock striking without pause until the box decides to stop it. The box learns when to halt the chime by watching a switch on the striker, which counts how many chimes have happened. A separate switch on the clock shaft sets off an hourly signal, telling the box exactly when to begin chiming.
The box runs the clock motor, and the “reset” switch seems to serve no purpose beyond cutting off the motor. The “advance” button must be pressed down for several seconds before it does anything at all. Once released, the clock sounds its chime; pressing and releasing again moves on to the next hour.
The clock’s time is set by pressing advance until the correct hour shows up. A flashing code appears on the “Status” LED — long long, short short short — though the writer assumes the number of flashes does not match the time. There was no time left to work it out before departing.
No actual clock face exists inside the box; instead it holds a simple counter marking the hour. The timekeeping itself derives from the “hour trigger” switch taken from the main mechanism. Two switches link through banana plugs, and the box includes cables for the BST/GMT switch, mains power in, clock motor out and chime motor out.
“We had a slightly stupid moment when we thought we’d got it wrong, and the clock was running backwards.”
A test that didn’t happen
Aiming to put the clock through its paces, the writer wished to hear it strike thirteen times or ring on without pause. Yet they found themselves surrounded by a group of people in the tower who refused to permit it.
The writer’s own notes point toward testing the battery, and raise the question of whether the reset switch might set the time back to midnight — both left open for answers at a later date.
What we learned
The Portobello Police Station clock is a working machine from 1877 that has been patched and repatched over more than a century. The microcontroller box, while baffling, seemed to work — and the writer and a friend now know exactly how to set its time.
This tale serves as a reminder that the machinery of public life frequently operates through makeshift repairs, patched-together components, and the accumulated wisdom of countless generations of people who merely kept fixing things.
The writer’s ascent, the spiders, the attic and the enigmatic box combined into an afternoon of real surprise and joy — and a clock that is now correctly set.
Key facts
– Built: 1877
– Microcontroller: PIC 16F628, presumed date-code 2001
– Chime control: “advance” button, “reset” switch
– Code on Status LED: long long, short short short
– Open questions: battery test, reset switch behavior
Source material: “Fixing the Portobello Police Station Clock,” pointinthecloud.com.
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