Installing a sound decoder - 7
buy packs of five resistors of the same value for about $2.
(Unfortunately they do not carry all of the standard sized resis-
tors but I have tried to specify resistors that Radio Shack stocks
so modelers won’t have to drive for miles looking for an elec-
tronics shop).
For LEDs, a 1000-ohm resistor works well, as will a 680-ohm or
even 1200-ohm – LEDs are not fussy. Just remember that the
blue decoder wire is positive, so the Function wire will go to
the negative lead on the LED, the one by the flat spot on the
flange.For 1.5V bulbs, it gets a little sticky since the wattage
(current) of the bulb determines the resistance, so there is no
“one size fits all” dropping resistor.
However, if you know the current rating of the bulb(s) you will
be using, a 15-milliamp bulb will need a 680-ohm ¼-watt resis-
tor and a 30-milliamp bulb will need 400-ohms of resistance.
However, a 30-milliamp bulb at full brightness draws about
0.32 watts, enough to get a ¼-watt resistor very hot! The quick-
est way around this is to use two ¼-watt resistors wired in
4: How to connect
two resistors in
parallel; note
that small shrink
tubing is used
first, then a larger
size is shrunk over
them to cover the
resistor leads and
cover any bare
wires.
4
MRH-Dec 2013
