The PRIZM Sound Board User's Manual
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17
P = (3.7 - 2.9) * 1.5 = 1.2 W
Ideally a 1.5 to 2 W resistor is recommended in this case.
Resistor bargain
As seen in the example above, a 0.56 ohm resistor might not be easy to find. Also, the
user should not focus on the absolute precision of the resistor value if he is still within
the LED specifications and ratings. Instead of looking for an expensive source of a
rare resistor, the user can craft his own using 2 (or more) resistors.
Without going too much into boring details, there's a simple rule of the thumb saying
that wiring 2 identical resistors in parallel divides the resistor value by 2 and multiplies
the wattage by 2.
In our previous example, a 2W, 0.5 ohm (ish) resistor could be obtained with 2 x 1 W,
1 ohm resistor.
Use either ceramic or thick carbon film
resistors only as your high-power LED
resistor (NO metal film). When combining
them in parallel, ceramic resistors can be
directly wired directly. In the case of
carbon
film
resistor,
I
recommend
individually wrapping them in heat-
shrinking tube to avoid shorts if their paint
chips (which sometimes happens if they
are touching each others)
If the resistor calculation ends up providing either a very small resistor value or a
negative value (!), you might skip the use of a resistor and adjust the LED drive
instead. Refer to the color profile section for more details.
2 x 1W 1Ω
= 0.5 Ω 2W
R1
R2
