QUOTE (Richard Johnson @ 3 Nov 2008, 13:40)
<{POST_SNAPBACK}>*** If you are talking about how to add a resistor to an LED then it simply goes in line with the anode/positive LED lead of each LED. The correct resistor value will depend on the LED type and the actual supply voltage you use.
If you are talking about adding another LED to a signal which already has resistance built in, then it only needs to drop the voltage difference between the 12v recommended and the actual supply voltage.
To calculate the resistance you need to use ohms law which is in simple terms, amps = voltage divided by resistance.
But: you ideally need to know the power dissipation of the LED - I doubt eckon actually mention it but most reds are about 5mA (can anywhere between 2 and 7.5mA for a standard brightness 3mm red LED)
If your LED is 5mA and you need to drop all of the added 3 volts between 12 and 15v then... is voltage divided by current = resistance
which is 3 / .005 = 600 or 5mA = 3v / 600 ohms.
or
3 / .005 = 600.
If there are NO resistors already supplied or fitted then just use anywhere between 1k and 2k ohms - it'll be fine.
As a convenient option, signals are usually too bright as supplied anyway - try powering them with a 9 volt mobile phone charger. (and any resistor as supplied of course)
how are you going to switch them / power them?
Richard
I had hoped to switch them using the ECos via an accessory decoder.
Power supply I'm still looking for something 12v or below.