The led is digikey pn 350-1526-ND.  It is made by dialight (their pn 558-6003-007).  Here is the link to the digikey catalog page with the specs: http://dkc3.digikey.com/PDF/T053/1652.pdf

Is there a formula to calculate resistor size values for switch and led applications like this? 

Thanks again!
Chris

On 12/22/05, Dave Hylands <dhylands@gmail.com> wrote:
Hi Chris,

>  So if I understand correctly I have 2 lines (wires) coming off of GPIO 59.
> One of those wires goes to my switch, which then goes to ground.  The other
> goes from the GPIO to the resistor and from the resistor to Vcc.
>
>                    |-------resistor--------Vcc
>                    |
>  GPIO--------|--------switch------GRND

Yep - that's exactly correct. Although, I would probably conenct the
two wires together at the switch rather than at the breakout board,
just because there's more room to play with :)

>  Since I am using the breakout-gs new version with Vcc as battery voltage
> (which I guess is 5v with the wall wart) is there anything different that I
> would need to do to step that voltage down to 3.3v or does the resistor do
> all that?

I think it's the older breakout's that suffer from this. The newer
ones should be OK. You can check by measuring Vcc.

Using a larger resistor value, rather than a smaller one would be
appropriate then, although 10k is probably still fine.  I use 10k
inline resistors to connect 5v to 3.3v, and for many devices this is
fine.

If you're paranoid, connect two resistors together. Connect R1 from
Vcc to the R2. Connect the other side of R2 to GND. Make R2 be double
the value of R1, and the junction between them will be at 3.3v (if Vcc
is at 5v). Connect your pullup to that. I'd make R1 be at least 10k.

>  The led I am using is blue.  I don't have the part number with me now but I
> can get its specs if that would be helpful.

Yes - that would be useful.

--
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/


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