On Mon, 11 Jan 2010 21:06:32 -0500, Charlie Smith
wrote:

I have cobbled together a circuit from available internet sources to
illuminate a homebuilt aircraft instrument panel. I was wondering if
those qualified in this group would mind reviewing the schematic and
making constructive commentary. I'd like this thing to be reliable and
not cause a host of other electronic gremlins. Just keep in mind, I'm a
chemist, not an electronics professional. But, I do learn quickly.


Thanks.
Charlie Smith

Safety- it definitely needs fusing and, as Jim suggests, EMI from the
switching could conceivably screw up your radio communications or
other instruments. Maybe not enough DC current to worry about, but you
also should be aware that heavy DC currents can affect compasses, so
wiring layout may need a bit of care.

You could also consider a premade solution like this one:

http://www.digikey.com/scripts/DkSea...me=788-1023-ND

The 350mA constant-current dimmable version is less than $20 at
Digikey. There still be some EMI, so it has to be checked that it
doesn't cause interference (eg. with weak radio signals). You could
probably reduce the 68 ohm resistors to 33R without any problems.

You also need some kind of reliable backup for when this thing fails
and it's dark. Consider an on/off/bypass switch that would replace the
electronics with a resistor.