| ??? 11/10/09 23:56 Read: times |
#170664 - that seems very nearly feasible ... and almost affordable Responding to: ???'s previous message |
Per Westermark said:
Let's take this module:
http://www.futurlec.com/LED/LEDMS88O.shtml If I put one LED behind each character (and the total display has 10x11 characters), then I will need 4 modules (total cost) $1.90*4 = $7.60. Each LED is 3x3mm. CC distance is 4mm. The total area for the text would then be 10*4mm x 11*4mm = 40mm x 44mm. A nice small display. Nothing fancy for the wall, but a perfectly capable solution for a school project - the complexity of the task isn't much affected by the physical size of the resulting clock. I'll agree with that. This also explains why you'd multiplex them. There are problems, of course, in that the light from a given LED isn't collimated, so you'd have to build some sort of grid to occlude light from "bleeding" from one column or row to the adjacent one. That might be "doable" particularly if one had a felt mask and used a punch to make holes in the felt mask. However, you only have sixteen columns of 16 rows. Will all the required words fit in that space? Anyone who feels that this is too small, can upgrade. Design with 2x2 LED behind each character. The CC distance for the characters will then be 8mm. The total area for the characters will be 80x88mm and the cost will be $30.40. Splitting a series resistor to both anode and cathode side, you could cheat and drive two rows at the same time, since the two rows are expected to display the same information.
Using this matrix http://www.futurlec.com/LED/LEDMS57R.shtml with 2x2 LED/character, you would need 15 modules (X: 5*5 = 25 diodes - 22 needed) (Y: 3*7 = 21 diodes - 20 needed) total $25.50. That would give a character CC of 10x10mm and a total character area of 110x100 mm. Using 3x3 LED/character with this module would require (X: 7*5=35 diodes - 33 needed) (Y: 5*7=35 diodes - 30 needed) 35 modules => $52.50. 15mm CC for the characters and 150x165 mm text area. As you can see, a LED matrix behind the clock works quite well as long as the display is reasonably small. And if you make the clock large, then the amount of light behind each character will be much higher which may make it hard to get your suggestion of 3 LED to produce enough light in case the sun shines on the wall where the clock is hanging. For a large wall-mouned display, LED, aside, perhaps, from modern high-power LED's might not be a good solution. An incandescent might work better. There are devices available that diffuse light from a single high-power LED to a 10cm-long (or less) backlight and those are off-the-shelf items that cost very little from the right source. Further, one can easily whittle them from various clear plastics and simply put a white or other color transluscent mask behind each word. That would add more manufacturing effort, on one hand, and reduce the wiring/coding/etc. on the other. Yes, I think this could be an approach affordable my most students today, and achievable by them as well, if the 256-characters spaced in 16 rows of 16 columns are adequate. the sort of words I thought might work are as follows. The spaces are arbitrary and could be zero, as would be required by the sort of array you suggest. The time is One Two Three Four Five Six Seven Eight Nine Ten Eleven Twelve Thirteen Fourteen Half Quarter Sixteen Seventeen Eighteen Nineteen Twenty One Two Three Four Five Six Seven Eight Nine Till Past One Two Three Four Five Six Seven Eight Nine Ten Eleven Twelve Thirteen Fourteen Sixteen Seventeen Eighteen Nineteen Twenty One Two Three Four Five Six Seven Eight Nine Till Past One Two Three Four Five Six Seven Eight Nine Ten Eleven Noon Midnight AM PM perhaps fewer words will do ... It's up to you. RE |
