[simpits-tech] Resistor for LEDs?

[Mike Williams]

Thanks for all your input, Stig & Chester, I have a way better understanding
of wiring them now, would be a great write-up for the website.
Merry Christmas

> 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
>
>
>
>
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