[simpits-tech] Resistor for LEDs?

[Stig Joergensen]

If you are using the 3.3 volt line, put in a diode ( -|>|- is the
symbol), but remember the current (amps) - you will need a rather big
one (the 1n4148 will only handle about 1 amp iirc)....

wire it like this

           _
          | |---|>|---
3.3 ------| |         |---- to leds
          |_|---------

when the switch is in down position, current flows directly to the leds,
hence 3.3v on the leds - in up position the diode will give you a 0.7
voltage drop hence only 2.5v goes to the leds

in theory this should work, but i havnt tried it my self....

you can also as suggested by Chester do like this :

         _
        | |---|>|----
5v -----| |          |----- to leds paired in two
        |_|----------      


but i think the amount of wiring is about the same, but fault finding
might be easier with the 3.3v version (remember the "Christmas light
string" - if thats the word??? - where one bulb blows and the hole/part
of chain goes dark).

Further more - the "lightwire" that goes to the panel, must be relative
thick (eg use a thicker wire than the signal wire) otherwise you will
also see brightness different depending on how close to the PSU the
panel is - the reason for this is the amount of current you are drawing
and even cobber wire have some resistance and the smaller the more
resistance, hence a bigger voltage drop on the wire itself (u=r*i)

ex

1000 feet of 10 gauge cobber have 1.02 ohm of resistance @ 15a = 15volt
drop
1000 feet of 40 gauge cobber have 1070 ohm of resistance @ 15a =
16050volt drop

so you see, if you need to "transport" 5 volt with 15amp across a
distance of 300m not even a 10gauge wire is big enough (these are
extreme - i know - but just so you can see it will make a difference)

for further info on cobber wire have a look at this :
http://www.valhallascientific.com/applications/applications-6.shtml


hope this wasnt to hairy for you....


Merry x-max, in denmark we celebrate the birth of christ on the 24th and
in 5 minutes its the 24th

/Stig