I was reading this web page about the history of mystery clocks and I got some ideas. One of them I got from my experience with a very old automated voltmeter. I don’t remember much about this voltmeter other than it used many relays and made a lot of noise and the display consisted of windows, each window ten or more rectangles of plexiglass, each one having one of the digits and possibly a decimal point, and they were all stacked one behind the other. I think there were four or maybe five windows. As the number changed, a small light would come on and illuminate the edge of plexiglass for that digit, and the digit could then be seen in the window.
My ideas for this clock are not supposed to be designed for the best visibility or ease of interpretation. The original round clock with the big hand and little hand was not designed to be easily readable, and we all had to learn how to read it when we were young. My design is supposed to be somewhat like the original clock. If had wanted to design it to be easily readable, I would have used four digit windows similar to the four digit voltmeter.
These mystery clocks used the sheets of plastic to hold the minute and hour hands of the clock, so it looked like the hands were suspended in the air, with no apparent means of being moved. Instead, I thought it would be very cool to have the minute and hour hands etched into sheets of plastic, with each sheet illuminated from the side.
The hour hand would need to have twelve sheets of plastic, each one with the hands positioned around the center similar to the original clock. Each digit could have the 1 through 12 digits etched at the point where the hand is pointing. Another alternative could be a single sheet of clear plastic with twelve minute hands etched into it, one pointing to each of the twelve hours. There would be twelve LEDs, each positioned around the circumference, pointing to each of the twelve hour hands. But I’m not sure that there would be enough isolation between the hands, so it might look like there were three or more hands illuminated instead of just one. A solution to this might be to etch a deep line betwen the hands and fill it with black paint to block the light.
The minute hand would have to be much more complex, it would require 60 sheets, one for each minute, or a single sheet with sixty hands etched into it. I think the stack of sheets would be too thick for the clock, or it would be impossible to illuminate just a single minute hand. So instead I thought that it would be better to have two windows, one with six sheets, 0 through 5 on the left, and 10 sheets, 0 through 9 on the right. Then the minutes 0 through 59 could be indicated with only 16 sheets. There could also be a sheet for AM or PM, or else the LED color could change from yellow for AM to blue for PM, for example.
Instead of stacking the minutes digits one behind the other, they could be two rows, the top row with the digits 0 through 5, and the bottom row with the digits 0 through 9. The rows could be below the clock face, or on the side, arranged as columns, either both columns on one side or one column on one side, the other on the other side. But I’m not so sure this would be as easy to read as both on one side. The problem with the columns is that it would be less symmetrical than the rows at the bottom. Perhaps it would be a good idea to add two more ‘digits’ to the tens of minutes column for AM and PM, making a total of 8.
I know that the easy route would be to just put a third row of 12 more digits for the hours and skip doing the clock face. It is really tempting to go this route. But in this case technology must not triumph over art.
The Electronics
There could be several different ways to decode the time to get the power to the LEDs. One, most straightforward, would be to use some decimal decoder chips, one for each digit. The driver could be a microcontroller chip with a precision crystal oscillator for accurate time. Or the clock could use a dedicated clock chip, but the output might be in seven segment, which would require further decoding. Another way could be to use a quartz clock movement for the precise timing and replace the mechanical part with a resistor, and use the 1 second pulses for the clock. The microcontroller could sense he pulses and advance the time. I don’t think the circuit would need to be multiplexed because there is no need to minimize the pins on any display. The displays are just LEDs, and all that is needed are registers and decoder chips. When I think about it, the clock only requires counters, not a microcontroller, because there are no decisions that need to be made.
