[Robotgroup] LED's and Resistors?

[Paul Atkinson]

John,

These links can help you pick the values for single LEDs and multiple LEDs
respectively. I'd assume 20 ma current for a bright LED.
http://led.linear1.org/1led.wiz
http://led.linear1.org/led.wiz

You should be able to get resistors at Radio Shack or Frys or MC Howard. The
values are usually printed on the package so you may not need the color
codes. (At MC Howard they are loose in bins, so you need to know the color
code or take a multimeter with you.)

This link has a color code decoder:
http://www.dannyg.com/examples/res2/resistor.htm

The method Andre' mentioned will work also.
Paul

On Thu, Apr 3, 2008 at 2:24 PM, Andre Lamothe <ceo at nurve.net> wrote:

> Well, the lights are in parallel feeding off the 4.5V supply, so you can
> tap
> off that and if you want create a "voltage" divider circuit to generate
> the
> 3V, depending on how many "loads" you put on the voltage divider it will
> change the divider and the voltage will vary, not that important in a
> simple
> circuit like this, but a concern. Additionally, the ugly part is that it
> will waste power -- Voltage dividers aren't a good way to generate POWER
> SUPPLIES -- they are good for signal control and scaling though--
>
> Instead, here's a trick get (2) 1N4001 diodes -- when they are foward
> biased
> they will drop about 0.7 volts each, (2) in series will drop 1.4ish volts
> and viola you have your 4.5 - 1.4 = ~3V, no power wasted, and the voltage
> will be very stable over the range of current you pull. So, here's the
> circuit --
>
> From xmas light power supply
>
> +4.5V ------------------------ +D1- ----------- +D2- ------------------>3V
> Output
>
> -(GND)
> -------------------------------------------------------------------*
>
> Where D1 and D2 are 1N4001 diodes or similar (1N400x) the various "x"
> change
> the current rating. And + means anode, - means cathode (the side with the
> line).
>
> And get 3-4 Diodes, you might want to start with 3 diodes and your load,
> see
> how it does, then back off to 2 diodes.
>
> This is called a "diode regulator" and a great way to downstep a voltage
> in
> a pinch without a full regulator. But, its input (the 4.5V) needs to be
> regulated, since the regulation of the the output is only as good as its
> input --
>
> Andre'
>
>
>
> ----- Original Message -----
> From: <john at cozmicfunk.com>
> To: "The Robot Group Mailing List" <robotgroup at puremagic.com>
> Sent: Thursday, April 03, 2008 2:10 PM
> Subject: [Robotgroup] LED's and Resistors?
>
>
> Hey there. I have a basic question for anyone who can help.
>
> I have a 4.5 volt (3x AA) DC powered LED circuit with White LED's (x-mas
> lights string from Walgreens etc.) and I am adding 3 volt Red LED
> flashing circuit to it. I need to step down the voltage reducing the
> input for the flasher to 3 volts ( obviously reducing 1.5 volts from the
> input).
>
> I have a couple different flasher lights and LED compartments (all 3
> volt DC) I am adding down the line for my hallway sections on my models
> sets. I understand there is color coding on the resistors, which ones
> should I get and where do I find them, Rat Shack , Fry's etc.
>
> This should be simple for people like Andre and Vern and Done and Gray
> etc.
> Thanks, John
>
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