Some of my clocks

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A few of my homemade clocks


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CRT vector clock

Since putting up these images I have had several people ask about this clock in particular. This vector clock is a microcontroller running D-to-A for X and Y, but Z (intensity) is digital. The amplifiers for deflection and CRT cathode (brightness) are triodes, with the X and Y being differential pairs. Differential amplifiers are needed to keep the beam focused across the screen. In order to move the beam, you raise the voltage at one deflection plate and lower it the same amount at the opposite plate. This causes deflection while keeping the average potential the same, so it doesn't disrupt focus as would one fixed and one variable deflection plate, which is sometimes used.

The power supply, as you might guess, is nasty and complex. If I remember correctly, the deflection circuitry runs on about 300 volts and the CRT anode runs on about 800. This is pretty low anode voltage but I got decent focus and brightness. The X and Y D-to-A outputs are direct-coupled to the triode grids (!) so bias on the differential amplifiers is set by moving the entire logic power supply up and down with respect to the tube supplies. I think the software is intersting in itself - for instance I digitized my handwritten numbers to generate the vectors, so the clock is uniquely mine in that way too. To minimize screen burn, the image sweeps across the screen throughout the day. You don't notice it moving, but it does.

On the back of the clock is a center-off momentary switch for setting. When you push it one way, an underline moves under the number to be changed. When you push it the other way, the number increments. Since each digit is set individually, you have to click five, not fifty times, to set the time to xx:50. After setting, the screen clears and you are presented with an underlined 12 or 24 to choose the time display mode. The seconds start running only after the final click to exit set mode (when the underline disappears) to allow synchronizing the seconds. I haven't seen this scheme used for setting before, but it works surprisingly well and allows you to set the clock in just a few seconds, with no irritation. I think most clocks set badly (the FAST and SLOW buttons on commercial alarm clocks are the worst design ever.)

For handwired stuff I never draw out a schematic; I just build from my head. So other than sharing the general idea like this, I unfortunately don't have much else. I certainly don't have anything like a full schematic for this clock. I'm trying to get better about that, but old habits die hard.

Its neat display.

A clock made from one giant nixie tube.

I turned the simple case from a piece of canary wood on the metal lathe. It's finished with just oil to preserve the interesting natural color. The clock only has one digit, so to show 11:32, it shows 1 1 3 2 (pause) 1 1 3 2 (pause) ... The numbers quickly fade in and out, giving a pleasant look. This one is fun because, often, people don't realize it's a clock at first glance.

Its guts showing. Close quarters!

WWVB Clock

Possibly my favorite clock. It sets itself from WWVB. Run entirely by one vintage F8 microcontroller (lower right) with its piggyback ROM containing the program. This clock was built in '01 and has been running constantly since. The ultra-long-life (mercury added) tubes show no sign of darkening/aging. Since the WWVB signal provides only the day of the year (1-366), the clock has to calculate month/date. Since March 1 is sometimes day 60 and sometimes day 61 (leap years), the date algorithm has to know about leap years. The very complex code in this clock was not fully tested until I woke up and checked it on the morning of Mar 1 '04! Happily, it worked correctly.

Calculator rebirth

This row of tubes came from an unrepairable calculator. This clock was a gift for my brother. I like the glass cylinder idea for the case. The number on the right is the date, and when setting you tell it the month so it only requires a reset on leap years. It displays tenths of seconds, making for a showy display. I should get a better photo someday.


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