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12ft GPS Wall ClockIt's the project that just kept getting larger. We combine some LED light bars with a simple controller and a GPS receiver. About 6 months ago, we discussed creating a 6' tall alarm clock - authentic down to the Timex face plate. While this may sound like a silly idea to begin with, it quickly became obvious just how difficult it would be to build at that scale so the project was scuttled. Recently, I came across a source for pre-package LED light bars that rejuvenated my need for a big clock. Why not? I now hate Styrofoam. If you want to replicate any part of this project, prepare to have little white balls all over your work area. So here is the little project that grew to 12 feet. We added a GPS receiver so now we have a 12' clock that sets itself, displays hours/minutes/seconds, and is accurate to 100ns. Beat that bed side alarm!
The Clock Firmware is available here! C ASM HEX Things I used - You may want to skip over this section for now. This is just a list of all the tools that are needed:
Getting the light source - These light bars, as I like to call them, use three LEDs and run on 12V. Why use them? They come pre-packaged with current limiting resistors and nice plastic carriers. This made it easy to create arrays of a large number of super-bright LEDs, without all the hassle and labor of creating our own custom configuration. Get the LED Light Bar here! Each stick uses about 30mA @ 12V. This is actually pretty good considering how bright they are. 30mA is a fraction of what an equivalent neon tube would pull. It started out as just hours and minutes. Then it was obvious we needed a colon. Then the seconds were so cool that we just had to have them, so in the end, it was two colons and 6 digits. In all:
92 bars are used. If every segment was on at the same time, we would need :
2.76Amps! At 12V is ~33Watt power supply. This is not small by any means. Come to mention it - perhaps we could use an ATX power supply... Hmm... Maybe later... At this time, we are using a basic variable bench power supply from Mastech, the HY1803D. With an 18V 3A max output, it handles the 12V @ 3A requirement easily. Finding the Digit to copy - Originally I was going to simply screw the light bars onto the wall in a 7-segment digit configuration. That's where things turned south. The LED bars are fabulous! But the LED intensity is so high, it's painful to look at. So we needed to diffuse the LED light a bit and create a better shape to the light. Shopping at the local Home Depot produced a large selection of potential options. Using a Styrene sheet of plastic (commonly used with 24x48" fluorescent panel ceilings) l was able to get rid of the 'spots' of LED light. The problem was that the styrene had to be ~2" away from the LED to get rid of the spots. I am not an optics engineer. So I decided on using 1 1/2" sheet of Styrofoam to create a light box of sorts around each set of light bars. Oddly enough, the sheets of Styrofoam came in 24x48" sheets as well. So did the 1/8" fiber board (lighter, cheaper, and easier to cut then real wood). So it was decided! The digits would be 24" tall. Perusing the Digikey catalog for a worthy victim, I settled on the datasheet for the LSHD-5503 7-segment Red LED display. Zooming into the PDF, capturing the digit, cropping, etc. No big deal. Here is the slightly enlarged digit with segment assignments: I could replicate this! So I increased the print size to 24". Using MS Publisher to create a multi-sheet printout of standard 8.5x11" sheets of paper, I taped the pages together and cut out the segments - I had my stencil! The 24" Digit Stencil Now it was just a matter of transferring from the stencil to the various layers of the final digit. Couple thoughts mid-conversation here - I decided to split the clock into multiple digits. This simplifies manufacturing because you just have to make the same framed digit, as many times as you need. By separating the digits, you get rid of any ugly seams in the middle of your clock (imagine the cost and hassle a of a 12' single sheet of plastic). This also simplified the wiring - 7 segments means 7 signal wires and 1 return wire (either power or ground) is needed. 8 wires - wait!! Cat5 cables have 8 wires (4 twisted pairs). Suddenly, it was painfully simple and obvious that we should split things up and use pre-terminated, cheap, easy to find, Cat5 cable to connect all these digits to the controller. Neat! Nuther note : I used the paper stencil many times on different layers. This was a bad idea. The paper flexes and moves around causing different layer material (fiber board, Styrofoam, or foam board) not to line up. These mis-alignments are very apparent when light starts being shown through the segments. I learned only half way through to create a master foam-board stencil. This rigid stencil moves less and creates much better alignments. So once you have your stencil created from a series of 8.5x11" sheets of paper, transfer that to an 18.25" x 24" sheet of foam board. This will now be your master stencil. Here are how the layers break down:
The Fiber Board and frame support the digit. The 1.5" thick Styrofoam gives us distance from the LED source to the Styrene to reduce LED 'spotting' and helps block light from one segment spilling over to another segment. The Foam Board gives us nice straight edges to the light - makes the segments look clear (getting Styrofoam to cut cleanly is next to impossible). The Styrene top layer disperses the LED light and gives the digit a white colored face. |
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I would be interested to see a schematic of some sorts, even a simplified one would be nice...
thanx!
can you pls put up the schematic of the board on the site???
http://www.youtube.com/watch?v=rkOoHor347s