Plastic dollar store skulls

[Warlock]

I have airbrushed about 20 of these to look like real bone etc...Now I want to light up the eyes only with an led each.Batteries run out too fast so I wanna control em by the computer and possiblly RPM's dc ssr design as well as use it for the mighty mini's...Can anyone give me some hints on a voltage as I simply want to fade the eyes in and out etc....But they have to be on together...
Thanks as always

[n1ist]

The easiest way would be to wire the two LEDs in series, and connect them to one channel through a series resistor or constant current source. The voltage and resistor depends on the type of LED.
/mike

[chilloutdocdoc]

I agree with n1, the easiest way would be to wire them in series... it'd look something like this

== ( * --- * ~) ===
wire in - 2 led's wired in series - resistor - wire out

[n1ist]

And in case that ASCII art is a bit confusing,

[chilloutdocdoc]

And in case that ASCII art is a bit confusing,

yes it is, much better representation, i should've really taken the time to do a schem

[Warlock]

Thanks guys now how do I figure out the resistor without knowing specs on the led ???

[Jrd]

Oh so they already have LEDs in them? I think you need to measure the forward voltage on the LED but I am not 100% sure on the details.

[Warlock]

I wired em up but the thing is I'm not sure of the resister value...All I did to wire them up was to take the leds off the board of the light I got to steal em from...Then I simply drilled the holes for the eyes then installed the leds...I'm not sure of the resister value for them..

[budude]

I wired em up but the thing is I'm not sure of the resister value...All I did to wire them up was to take the leds off the board of the light I got to steal em from...Then I simply drilled the holes for the eyes then installed the leds...I'm not sure of the resister value for them..

I would guess these are going to be "standard" 20mA LEDs - in either case, it's probably to start there and see how they look anyway - you can always go up in power later. "Typically" Red LEDs are around 1.9-2v and Green/Blue/White are 3-3.2V. Just take the drop necessary from your supply voltage. If they aren't Red, then you'll probably need at least 6-7V in to power two LEDs.

Let's assume they are Red at 1.9V and are 20mA and you have a 9v supply. 9v - (1.9 x 2) = 5.2V drop. 5.2V / .02A = 260ohms or the next higher standard value. Power would be 5.2V x .02A or 104mW so and 1/8W would work but probably run pretty warm - I would go with a 1/4W unless you're strapped for room or something (guessing not).

Anyway - you could start with that and see how it looks. Of course plug in your own actual numbers to the calculations. It's a bit tough to give exact numbers w/o knowing the specs of the LED... Can you put a known quantity for the LED - like get a couple from Radio Shack or something since they will have the specs on them?

[Warlock]

Ok the only numbers I have are this...5 leds in series were attached to 4 aa batteries...Not sure if this helps but it's all I got...It was an old bike light I had lieing around and took the leds outta it..The read light I had (which is red) has the same config as the white I meantioned above...5 leds working off 4 aa batteries...Battery life is about 4 days (24/7) solid on before the batteries start to die out....

[Jrd]

So if the leds are connected straight to the batteries then they are running at 1.5v * 4 = 6v / 5 = 1.2v each. So you need a resistor capable of taking your power source down to 2.4v for two LEDs if I am correct.

[Sparkey]

I have airbrushed about 20 of these to look like real bone etc...Now I want to light up the eyes only with an led each.Batteries run out too fast so I wanna control em by the computer and possiblly RPM's dc ssr design as well as use it for the mighty mini's...Can anyone give me some hints on a voltage as I simply want to fade the eyes in and out etc....But they have to be on together...
Thanks as always

Take a look at this site: http://led.linear1.org/led.wiz
it will calculate and draw out your array for you.
Also, clicking on the ? buttons will give you info like a RED LED = 2.0 volts.

Have fun,
Sparkey

[DennyMo]

Thanks guys now how do I figure out the resistor without knowing specs on the led ???

Take a 9-volt battery, a 1kohm resistor, and your unknown LED, put them together like this:
http://www.kpsec.freeuk.com/images/ledtst.gif
Measure the voltage drop across the LED. Then do the math others have described or linked to to determine the actual resistor value you want.

This site has helped me quite a bit:
http://www.kpsec.freeuk.com/components/led.htm