Light guide clock part 9
Light guide clock part 9, originally uploaded by Black Heart Industries.
Shortly after this picture was taken, I managed to fry the four LEDs that are illuminated. Oops. Stopped, ate, and I’m now enjoying a Lagunitas Imperial Stout. Damaged LEDs have been replaced. I’m powering them from a Heathkit tri-power supply. I can’t increase the current with this supply. The LEDs become brighter and whiter with more current. White LEDs are similar to fluorescent tubes. They emit ultraviolet light that causes phosphor to fluoresce, producing visible light. When underpowered the ultraviolet light doesn’t excite the phosphor properly, so you see some of the ultraviolet, making the overall light blueish. The proper way to control the brightness is to use pulse width modulation. This means that the LED gets the current it needs to be the proper color and is just strobing at a very high frequency to reduce emitted light. More parts are arriving on Saturday, so until then, all I can do is start to populate the boards. These are the new changes: A way to supply a constant current is being added (allows control of color and brightness), external 9 volt power supply, internal 9 volt time backup battery (unplug the wall-wart supply and the display goes off but the clock is still running), and an old switch to set the time. The modules are 1.5″ x 2.5″ x 1.5″. The colon will be two LEDs in a 1″ wide piece of aluminium and will blink once per second. You’ll notice there is a three dimensional aspect to this display. I have some interesting light sensors in glass tubes, like electron tubes. I thought of using one as a way of controlling the brightness in relation to ambient light. It could dim the display when the room is dark. Maybe I’ll do that when I build a Nixie tube clock.
