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# Count Down Clock

NASA has one. So should we.

## Design

### Wants

 - Large LED 7-segment display with a +/- out front. HH:MM:SS
 - You can get ~ 1 foot ones around the internet, probably better than making one.
 - Something like a A6279 Constant-Current Latched LED Driver.
 - Some little μc (PIC?)
 - Is RTC overkill?
 - Serial (for other, future devices) interface (with commands like set, start, stop)
 - USB (for, say, the launch computer). Same commands as before)
 - Loudspeaker to announce 'Go, flight.', countdown, and 'Guidance on internal'

[Is this overkill? :)](http://www.sparkfun.com/tutorial/Clock/SFE-Wall-Clock-Big.jpg)

### Part Options

- [Sparkfun red 6.5" 7 seg $14.95](http://www.sparkfun.com/commerce/product_info.php?products_id=8530)
- [Evil Mad Scientist 12" 7 seg $55.00](http://evilmadscience.com/partsmenu/107-sevensegment)
- [Digikey 5" green 7 seg $32.60](http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=160-1024-ND)
- [Futurlec 9" 7 seg (board only) $30.90](http://www.futurlec.com/Lg_LED_7_Segment.shtml)

These are more expensive than I was hoping. The sparkfun ones might be the best deal though. Still easier than making them.

### Cost

[[!table data="""
Part               | Number | Cost [USD] | Total
7seg               | 6      | ???        | ?
Some LEDs (colons) | 4ish   | 1.00       | ?
LED Drivers        | ?      | ?          | ?
Power MOSFETs      | ?      | cheap      | ?
USB driver         | 1      | ?          | ?
μc              | 1      | ?          | ?
Board              | 1      | ?          | ?
"""]]

### Board layout

 - img preview
 - attach file