[dorkbotpdx-blabber] [GroupOrder] order goes out monday feb 23. guest star: sure electronics

[montyg at bittybot.com]

The current draw will depend on desired brightness.
20mA is the max you should try to feed continuously through the LED  
mentioned, but you can use lower currents for less brightness

Higher resistor values will result in lower current and thus lower brightness.

Calculate the resistor value as:
   R = (Vdd - Vf) / If
where Vdd is the supply voltage (5V for Arudino), "Vf" is the "forward  
voltage" of the LED (see the spec -- it varies by color; ~2.0V for the  
LE-DS151), and "If" is the desired "forward current", which will  
depend on the desired brightness.
So, the resistance needed to deliver 10mA to the Red LE-DS151 would be:
   R = (5V - 2V) / 10mA = 300ohm

An individual Arduino pin may be able to sink 40mA, but using all the  
pins to sink 40mA at once will be too much (there is typically a note  
in the spec about the max total current for all I/O.)

Monty


Quoting dan p <gunterhausfrau at gmail.com>:

> Just checked the first set of LED's and they call out
>
> "20mA Continuous, 50mA peak for 10% Pulse Width" should be fine with the
> arduino's"
>
> and from the standard arduino spec
>
>   DC Current per I/O Pin 40 mA
> no problems, what is the worst that could happen? make a little blue smoke?
> On Mon, Feb 23, 2009 at 4:02 PM, Daniel Johnson <teknotus at gmail.com> wrote:
>
>> On Mon, Feb 23, 2009 at 1:15 PM,  <montyg at bittybot.com> wrote:
>> > I can't speak to their quality, but I am ordering the following from Sure
>> > Electronics:
>>
>> I don't understand the specs well enough to know if these have
>> appropriate values for working with microcontrollers?  How much power
>> should they use?  They don't say what the values of the resistors are,
>> so how can I tell how much power they would draw?
>>
>> Qty 1 LE-DS151 100 pcs 5mm Red LED 4000mcd & Free Resistor
>> Qty 1 LE-DS153 100 pcs 5mm Green LED 15000mcd & Free Resistor
>> Qty 1 CS-CO059 Solderless Breadboard Jumper Cable Wire Kit 2 bundles
>>
>> Any advice on breadboardable switches?  I feel kinda lost even with
>> the most fundamental parts ordering, lights, wires, and switches.
>>  _______________________________________________
>> dorkbotpdx-blabber mailing list
>> dorkbotpdx-blabber at dorkbot.org
>> http://music.columbia.edu/mailman/listinfo/dorkbotpdx-blabber
>>
>