In designing any LED circuit it is the current that you need to control.
 The manufacturer generally specifies the maximum mA or the typical
operating current.
  You probably want to keep to about 75% of the maximum for long life.
 A cut and try approach is best, because different colors and types of
LEDs have different forward voltage drops.  When using a 12v supply you
can put 2 or 3 LEDs in series (+ to -, + to -, etc.).  If you start with
1000 ohms the current will be at a safe low level.  Put a meter in
series with the circuit to measure current and then gradually decrease
the value of the resistor to get the current up to a reasonable value.
  I like 15 to 20 mA for LEDs of the usual size.  If 2 or 3 in series
isn't bright enough, do another parallel branch with its own resistor.

Larry A.
home-brew LED maplite in AC outlet and LED behind heater controls
next, the domelites

nick greenaway wrote:

>does anyone know what parts i need to get at radio shack to drop
>12.6v down to 3.7v (i cant remember the amps) for an LED driver?
>im sure someone out there has done it
>thanx
>nick
>
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