Solder groups of 7 of the cathode wires to male pin headers (photo 8) - this will make it easy to connect and disconnect the LED board from the controller board. Make sure you test each of the words at this point - I had a few loose solder joints which caused only parts of words to light up. You can then attach a single wire to any positive lead (since they're all connected), and attach a wire to a negative lead for each of the words. Finally, bend the positive lead (resistor) on the end of each row down and solder it to the lower row to connect all of the resistors together (photo 6). Solder together all of the positive leads (the resistor side) in each row and solder together all of the negative leads leaving a gap (discontinuity) between words (photos 3/4/5). Tip: mark the division between words on the back of the cardboard - this will help when connecting LEDs. If you did this consistently, the leads of the resistors should overlap when placed into the cardboard backing. Make sure you make the bend close to the resistor/LED otherwise the leads might touch another row once installed. Take each of the LEDs and bend one lead 90 degrees, and the other 90 degrees the other way (see photos 1/2). test the LED-resistor combo on a 5v supply to make sure the solder joint is good and polarity is correct (photo 6) hold the short lead of the resistor next to the trimmed lead of the LED and tack them together with a bit of solder (photo 5) place the LED into some kind of jig to hold it steady - a piece of cardboard with a hole punched in it works well trim the anode so that a small stub ~3-5mm is left (it shouldn't even extend past the base of the LED) - photo 3 The anode is the longer lead, and is opposite the flat edge of the LED - photo 2 we're going to attach a resistor to the anode (+) of each LED. Keep in mind that up to 31 LEDs will be lit at once ("IT IS TWENTY FIVE MINUTES PAST ELEVEN"), so if you drive each LED at 20mA you will need a 620mA power supply - this is part of the reason why I planned for 10mA a piece.įirst, trim one lead of each resistor leaving about 3-5mm (see photo 1). I chose to use 1Kohm resistors and drive the LEDs at 10mA (half their rated current), but you might want to use 470ohm or smaller depending on your power supply and LEDs. We need to attach a resistor to each LED to limit the current that flows through it. Now comes the repetitive task of soldering all 98 LEDs and resistors. (Edit 8/1/10: Added a better description of the construction paper border and more pictures) Also, put a piece of black electrical tape behind each of the non-used spacer letters to make sure no stray light gets through. Tape this on the inside (back) of the letter mask to help diffuse the LED light and make the letters a dim gray when not illuminated. Now, cut out a square piece of the black garbage bag big enough to cover all of the letters. Tape the transparencies to the back of the border (photo 6). Use a utility knife to cut out the inner square leaving a 0.5" paper border (photo 5). Mark lines 0.5" in from each side forming an 8"x8" square (photo 4). Cut a piece of construction paper to be 9"x9". Therefore you need to cut a piece of construction paper to form a border and fill the gap - it also adds a nice touch of color. Note: the viewable area of the Ikea frame is 8.5" square, but unfortunately you can't print all the way to the edge of the transparency. Align the letters of the two layers and tape the layers together with double-sided tape on the top and bottom black regions - see photos 2 and 3. Depending on how dark your ink is you may need more or fewer layers to get an opaque black.Ĭut off the clear parts of the transparency so only the black square is left. The ink wasn't quite black enough to completely block out light, so I printed 2 of them and stacked them. Since there's a lot of black ink, I had my transparencies printed at Staples for something like 50 cents a piece. I thought of several different ways to make the letters, such as silk-screening on the back of the glass, or having a custom black sticker made, but eventually I settled on printing black onto transparencies - see the attached PDF file. The key to making the clock look nice was making the glossy black letter mask.
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