This is a breakout board for an arduino that boosts the 5v signal from the arduino output to a high-power 12v, suitable for running RepRap heaters, fans, heated beds, etc.
The IDC will plug into my Arduino Mega Shield ( http://www.thingiverse.com/thing:3308 ) and the power socket is designed to accept standard PC disk drive power plugs.
The signal from the arduino is amplified using a MOSFET - I used FDB8880 ( http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=1228327 ) at 60p each, which will handle 54A - which is way more current than I expect to ever need, or can be supplied from a single PC power supply.
There are also 8 separate outputs on the board - populate as many as you need. I'm a big believer in multiple redundancy.
It's a nice simple board and it is a good introduction to SMD soldering - each output is separate, so you can mess up one circuit and still use the other 7. I'm also not the most skilled or tidiest maker, and I managed to make it work :-).
This board is suitable for single-sided etching at home - I used the laserprinter method to produce a good board. I used a strip of Kapton tape to mask the ground line that runs just under the heatsinks, but the MOSFET legs bend over the top anyway.
The LED locations are duplicated - you can use a standard 5mm or 3mm LED as an indicator, or there are 1206-sized SMD pads if you want to use indicator leds left over from stepper boards. I used some extra-bright white LEDs I found on ebay.
The resistors are SMD 1206 and are 1kOhm ( http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=1576629 )
I used 4-way 5mm terminal blocks ( http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=1177877 ) but my holes are not quite the right spacing (I did some nasty drilling to force mine in). If you use 2-way terminal blocks, the spacing should be correct.
The 10-pin IDC header should be as per the RepRap stepper boards (v2.3) - http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=1298785
Version 0.6 uploaded. Now contains current limiting resistors and pull-down resistors to make sure board turns off if disconnected.