Mark's Next Challenge: Getting the Internet on His Watch

February 23, 2004

When he found a bunch of surplus miniature, alphanumeric LED displays, he knew he had the makings of a watch-but how far to go? Adding a barometer, altimeter, and temperature sensor makes it a perfect outdoor accessory. The coup de grace is the Trippy Bits / four letter word function-random bits sent to the display followed by a random four-letter word. It's better than TV.

Wrist-mounted entertainment center parts list
Amt Part Description Allied Part #
1 Battery holder, plastic 839-3480
1 Resistor chip, 4700 ohm 644-2120
1 Resistor chip, 1000 ohm 644-2306
1 Transistor, 2N3904 263-0429
1 Crystal watch, 32.768 kHz 614-0190
1 Schottky diode 950-1512
1 Capacitor, multi-layer ceramic 644-0260
1 Double-row pin header interconnect 900-2045
Additional parts required: 4-character alphanumeric display, PIC16F73 microcontroller, switch, resonator, temperature sensor, absolute pressure sensor, 24-bit ADC, printed circuit board, watchband, silicone adhesive

This project is the culmination of a lifetime obsession with all kinds of watches. I was too young in the early 1980s to afford the television watch or the tape recorder watch (yup, tape recorder) so I got stuck with a Casio model F-10. Finding a bunch of Hewlett Packard HCMS2010 4 character alphanumeric displays in a local surplus store got my imagination fired up about making my own watch. I had read about the Nixie Tube wristwatch, "The Four Letter Word"(an art project that flashes random four letter words), and various homebrew altimeters. I decided to cram as many of these things into a reasonable sized wristwatch as I could. I also wanted to have something useful to accompany me on my trail running adventures. The ability to log altitude data will allow me to keep track of how many miles I run - perpendicular to the earth's surface!


A well laid out, solder-masked printed circuit board is essential for this circuit. There are many companies in existence that will do small orders for a reasonable price, some of which even provide their own software. The cost of the circuit board is well worth the aggravation saved by not using a plug-in prototype breadboard.

The display draws about 150mA, depending on how many LEDs are illuminated, which rules out standard watch cells as a power source. Three AAA cells are not too much bigger than many commercial altimeter / thermometer / compass watches, so this was the logical choice. N cells would have made the whole thing narrower but they are more expensive and not as common. Carefully controlling the hardware (making sure no inputs float, making sure everything is shut down that can possibly be shut down, and making sure nothing is trying to drive a pin on a part that is powered down) keeps the sleep current to about 2 microamps.

The body of the watch is simply the battery holder itself. A nylon watchband is sandwiched between the printed circuit board and the battery holder, held in place with silicone adhesive.

Keeps on ticking and so much inside look at Mark's watch&

A PIC16F73 microcontroller running at 4MHz is the brains of the operation. The

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