LED Pocketwatch v1.0

An antique timepiece for the digital age

Build time: 20 weeks (over 2 years)
Development budget: $1000 + heirloom
Tools: Eagle CAD, Solidworks, MikroC


<update 12/11/10>
Ok, here's the current status: Circuit design and routing for v2.0 is complete. I've also gotten back in touch with the manufacturer of the cases I intend to use. I've got some free time coming up over christmas, so I'm hoping that I can get the new webpage up, order some boards and get a prototype assembled in the early new year.

A big thank you to people who continue to send me emails asking for design files or yelling at me to get a move on etc. Your enthusiasm is noted! However, I am right in the middle of my post-doctoral appointment and spare time is rare and precious - I don't want this project to become a second job!

I can, however, confirm the following features for the next version:
-Same LED layout, interface and controls as v1.0
-Stainless steel/brass case design
-2ppm accurate TCXO time-keeping
-30 days standy-by battery life (predicted)
-Compass chip and digital accelerometerfor compass-mode
-USB recharge and progamming function
-PIC24F processor to run everything

<update 14/7/10>
Thank you all for your emails - no, this project is not dead!

V2.0 is underway and will have its own page soon. The big delay at the moment is the lack of suitable modern pocket watch cases to house the new movement. The manufacturer I'd had lined up has disappeared...

If you know of a source of quality, stylish 52mm pocket watch cases, feel free to drop me a line and let me know!

<update 16/11/09>
A heartfelt thankyou to all the people who sent me emails and left kind comments on Hackaday, Make, Gizmodo, Youtube and more. Quick answers to the questions I've received:

1. "Can I buy it off you?"
No, sorry. It's made from an heirloom and not for sale.

2. "Where can I get one? Are you making a kit?"
They're not currently for sale - but I'm working on that. I'm currently working on finishing up v2.0, which will fix many of the issues in v1.0. When that's done, hopefully I'll be able to offer a kit using modern watch cases, as well as premade units.

3. "Can I get source code/design files?"
Since I'm working on a version that fixes many bugs, and which hopefully I can sell, I'm not planning to release the design files just yet. However, once the next version is done I will post them online.

4. "Have you considered using induction charging to charge the battery?"
I have considered it, but, as the Elgin watch brand was famous for its stainless steel cases, induction charging would only make the case hot. It might be possible to do with brass cases, but I've not looked into it. I might make this an option in v2.0.

The project
My grandfather was a horologist. When he passed away in 2005 I inherited from him a collection of broken pocketwatches. As my skills are in microelectronics, rather than micromechanics, I felt it would be a fitting tribute to him to produce an electronic movement in place of one of the broken ones he'd never had the time to fix.

The pocketwatch I selected was an Elgin hunter-style case (with opening cover), and appeared to be the most complete and in the best condition of those available. It's movement inside was stamped "Pat. 1925". It was also one of the largest to choose from, providing room for batteries and components inside. I resolved that no modifications or damage should be done to the pocketwatch case, or its movement.

Case and Disassembly
The case consists of several parts: the shell with one front cover and two back covers; the stem and crown (knob with shaft) for opening the front cover, winding the watch and setting the time; a time-set button that is depressed to change the time; a bezel that holds the front glass; and the glass itself - also called a 'crystal'.

Elgin hunter case Disassembled case Crown and stem

The stem operation on this case was smooth, and a light press pops the cover open easily each time. Unfortunately, the case didn't come with a bezel or crystal. I managed to scavenge a replacement bezel from another case, but I had to specially order a replacement plastic 'glass' to fit in it.

Disassembly is very easy. The back outer cover opens with the aid of a small thumb tab. The inside cover opens with the careful application of a thin blade. Similarly, a thin notch allows for the front bezel to be popped free. The mechanical movement itself is held in place by three small screws behind the back cover. Another tiny set-screw holds the stem in place. When all screws are removed, the stem pulls out and the entire spring, workings and dial face assembly drops free.

Clock Face and Circuit
I had the idea of using LEDs to represent the position of the hands, although I've since learned that it's been implemented in larger clocks before , but I've yet to find an example this small. There are 133 surface mount LEDs on the front face, all hand-soldered: 60 for seconds, 60 for minutes, 12 for hours and one for charging status. The great challenge was fitting all the 0603 LEDs and mosfets on the front dial; obviously, surface mount components were a must. The PCB is 44mm across.

To reduce the pin count, each set of 60 LEDs is divided up into six banks of ten, selected by a mosfet. Long circular tracks run around the outside of the board, connecting one LED from each bank to a drive pin. Each hour pin is controlled invidually. Everything is controlled by a PIC 16F946 - an 8-bit micro with plenty of IO pins. The spiralling via pattern this produces is quite aesthetically pleasing.

Unloaded PCB front Unloaded PCB back Loaded PCB

The clock face itself includes hour marks and Roman numerals for reading the time, as well as pin number markers on the centre IC. The outer-most LED ring is red for seconds, the middle is blue for minutes and the inner-most is blue for hours - this is in line with the standard relative lengths of clock hands. Underneath the chip is stenciled a tiger eye (a subtle reference to my grandfather's long-time association with the Freemasons). The watch is watching you!

On the reverse side is room for all the power regulation, charging, programing, precision timing and IO hardware. The watch runs off a single-cell 110 mAh Lipo cell, recharged through a jack underneath the back cover. The bottom side also has pads for a Temperature Controlled Crystal Oscillator (TCXO) capable of 1 part per million timing precision, although this hasn't been tested yet. A cell-phone vibrator is attached to the inside back cover; every second the vibrator pulses, using the cover as a sounding board to produce an audible 'tick'. The vibrator also serves as an alarm buzzer.

Loaded PCB LED pocketwatch Open back

User Interface and Programming
The watch is controlled by an encoder and two switches. The encoder (from Alps - the tiniest I have ever seen) sits in the slot milled in the PCB, and connects to the stem via a hexagonal channel sized to fit its square end, milled by hand. When the crown is depressed, the stem slides through the encoder and pushes a rotating disc against a switch. A collet and grub-screw hold the stem in place. The second switch is positioned behind the time-set button, although it has not yet been implemented.

The microprocessor was programmed in C using the MikroC IDE for 8-bit PIC microprocessors. Unfortunately, I only have the demo version of this software, which has a 2KB code-size limit. By far the hardest part of this project was writing my code to fit within this limitation; almost without exception, though, it made my code better, more streamlined and more elegant. I can easily say it's made me a better coder.

Most of the time, the watch will be in standby mode, with the LEDs turned off to save power. When the crown is pressed to open the case the stem switch is also depressed, bringing the watch out of standby and into display mode. The LEDs will progress each second, and when a minute or hour is incremented, a the LEDs will light through 360 degrees to advance to the next position, producing a decorative swirl. After 15 seconds of display, the LEDs will turn off and the watch will go back into standby mode.

To set the time, the stem is depressed and held in for 3 seconds to enter programming mode. The second hand will then stop incrementing and be set to the 12 o'clock position. Twisting the crown will cause the minute and hour hands to increment or decrement. Pressing the button for another second will exit programming mode.

The pocketwatch also has an alarm function. The alarm is set by holding depressing the stem for 1.5 seconds, whereupon the LEDs will begin to blink. Setting the alarm is handled identically to setting the time. Entering alarm mode sets the alarm on; it will stay on until programming mode is entered, or until the alarm rings. When the alarm goes off, the vibrator inside will pulse in time with flashing LEDs displaying the time.

LED pocketwatch Table top clock LEDs in the dark

The LEDs are very bright at night - so much so that they can be dazzling when you turn the watch on. To avoid this, an optical sensor was placed on the front dial. In display mode, the sensor reads the ambient light level and dims the lights if it's too dark, or brightens them if it's light. This way, the display is comfortably readable even in complete darkness or direct sunlight.

Status and Diagnostics
On first power-on, each LED is lit in sequence to test the electrical connections. There are two diagnostic display modes: the 'all ok' mode lights all the minute LEDs in rapid succession, producing a constant blue glow. The 'error' mode lights all the second LEDs, producing a red glow - this is also called 'red ring of death' or 'X-Box' mode.

Future Work
For v2.0 I have a shopping list of modifications to make. These include a modern watch case which I can cut a recharge port into - at the moment, the case has to be opened every time the Lipo needs charging. I will also use a lower-power, more compact TCXO chip to keep time - although I never tested this version with a TCXO, I have since identified much better ways of doing it. I would like to add sensors, such as accelerometers and a compass chip to use the display to show North. But the number one improvement will be the addition of USB, both for programming and recharging. The goal is to make a time settings and alarms adjustable with a simple application on a host computer, and also to have automatic NTP time updating whenever the watch is hooked up to a PC on the Internet.

For Granddad

Howard Pounds 1914-2005

Howard Pounds
master horologist

I never knew my grandfather very well, on account of our living some distance away from him all of my life. He struck me as a quiet, unassuming sort of man, but this fit very well with his astonishing skill as a horologist. In his heyday, he was among the best watchmakers in Australia. His steady and patient hand able to finely adjust the most diminutive gears and escapements of a clockwork mechanism. He was particularly recognised for his ability to perform delicate work in the smallest of mechanical movements, the lady's wristwatch.

During the Second World War, his expertise was considered too valuable to allow him to go and fight, and instead he was sent to fabricate precision mechanical systems at the Toowoomba Foundry. He was told that if he tried to enlist he would be arrested and sent back!

Such was his skill that when the Australian Horologist journal issued a challenge to drill a pin from end to end, he achieved it by boring a hole by hand, using tiny drills he made from sewing needles. Not one to let it rest there, he topped this feat by filing and turning down another pin on a minature lathe, and threading it through the hole. Then he raised the bar again with a three-penny piece drilled and threaded through the edge of the coin. He produced a small number of these pins and coins to amaze his clients.

Although he never got to see it, I'd like to think he would have enjoyed seeing one of his old broken watches turned into something new and useful. This project is dedicated to his memory.

Comments, issues: paul.pounds_at_gmail.com

Copyright Paul Pounds 2009