Electronics help needed: LED illumination for Sith wayfinder

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Plurpley

New Member
Hi all,

I've just finished making a reproduction of a Sith wayfinder from The Rise of Skywalker. For something that was made from material I had lying around the house, I was pretty happy with how it turned out. (FYI, the body is made from a cut-up Lego box, the panels are made from an old overhead transparency sheet, texture was done with hot glue and some home-made texture paste, then I painted it with Jo Sonja's acrylics and sealed it with Vallejo matte varnish.)

Now I really want to light it up, just like in the movie, but the problem is I know almost nothing about electronics. What I'd like to do is have two LEDs - one white always-on LED (to provide the main illumination) and one red flashing LED (to represent the navigational beacon) - connected to a small battery pack to be housed within the wayfinder. I believe the two LEDs may have to run in parallel, rather than be connected in series, but I'm not sure.

Is there anyone familiar with electronics for prop-building or cosplay who can help me out with a simple circuit layout and maybe some calculations for resistor values? I tried in the forums over at allaboutcircuits.com, but they weren't very helpful. I've attached an example of the type of circuit layout that I think might be required, but I'm really not sure. (Btw, the illumination in the second photo is from an electronic tealight candle, but it's just for reference purposes only - I'd really like to make something a little brighter, and incorporate the flashing red beacon as well.)

Thanks in advance!

(PS. In the meantime, I'm now working on a cardboard Blade of Ochi to go with the wayfinder - will let you know how it turns out)

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Sith wayfinder circuit diagram.png
 

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wdtenney

New Member
Nice job.
your schematic is clipped at the bottom when I try to view it, but I'm assuming that both LED cathodes are connected back to the negative side of the battery, in which case, the circuit should work fine. (assuming that you are using a red LED with a built-in flashing circuit - e.g. Lighthouse LEDs 5mm Round Top Red Breathing/Fading LED - Super Bright (Pack of 10) - - Amazon.com )

In order to calculate the value for the current limiting resistor, you will need to know the supply voltage, the LED forward voltage, and the LED forward current. The latter two values are found on the LED's data sheet or in this case in the description on Amazon.

For the example LED above, the forward voltage is 2.1V max. and the forward current is 20mA. Since the prop is on the small side, I'd suggest a power source of a pair of AA or AAA batteries. This will give you a nominal 3V supply.
If we plug these numbers into a handy online LED resistor calculator ( LED calculator for single LEDs ) we get a resistor value of 47 Ohms. The calculator will also tell you you can get away with a 1/8 watt resistor, but 1/4 watt resistors are easier to come by.

Hope this helps.
-D-
 

Blue Leader

Sr Member
Could you use a submersible LED tea light and put it inside? I got a set for a suit of armor I've been working on and they come with a remote (two remotes, actually) and can be set to all sorts of different colors, and can be set to stay steady, flash or fade.
 

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Plurpley

New Member
Thanks all, much appreciated. Not sure why my schematic was clipped at the bottom, the source image certainly isn't. In any case, as wdtenney has correctly suggested, the cathodes on both LEDs are connected to the negative side of the battery.

wdtenney , thanks for the link to the breathing/fading LEDs, they're exactly the kind of thing I'm looking for. Here in Australia, Jaycar have a similar flashing red LED, but I recently discovered that it has a 12V operating voltage, which is not going to be helpful for a small prop like this. The LEDs you've suggested seem to be a much better proposition. Now I just have to see if I can find an Australian supplier... (or wait six weeks for postage from the US).

I believe I will have to run the breathing/fading LED in parallel with the white always-on LED, otherwise they will both flash. However I'm not quite sure how to calculate resistor values for LEDs in parallel. In series I believe that the current remains constant but that the voltage drops across the series, whereas in parallel I believe it's the other way around (ie. the current is split between the two LEDs, but the voltage delivered to each is the same). I found one or two web articles on running LEDs in parallel, but they weren't very helpful. Can anyone help with calculating resistor values for LEDs connected in parallel?

Thanks in advance :)
 

wdtenney

New Member
Thanks all, much appreciated. Not sure why my schematic was clipped at the bottom, the source image certainly isn't. In any case, as wdtenney has correctly suggested, the cathodes on both LEDs are connected to the negative side of the battery.

wdtenney , thanks for the link to the breathing/fading LEDs, they're exactly the kind of thing I'm looking for. Here in Australia, Jaycar have a similar flashing red LED, but I recently discovered that it has a 12V operating voltage, which is not going to be helpful for a small prop like this. The LEDs you've suggested seem to be a much better proposition. Now I just have to see if I can find an Australian supplier... (or wait six weeks for postage from the US).

I believe I will have to run the breathing/fading LED in parallel with the white always-on LED, otherwise they will both flash. However I'm not quite sure how to calculate resistor values for LEDs in parallel. In series I believe that the current remains constant but that the voltage drops across the series, whereas in parallel I believe it's the other way around (ie. the current is split between the two LEDs, but the voltage delivered to each is the same). I found one or two web articles on running LEDs in parallel, but they weren't very helpful. Can anyone help with calculating resistor values for LEDs connected in parallel?

Thanks in advance :)
Yes, you would want the LED's in parallel as you have them in the schematic. I don't know the specifics of the flashing circuit incorporated onto that LED, so it may pass current when its' own die is off, but why take a chance?
Although the LED's are in parallel, each one has its' own current limiting resistor in series, so each branch of the circuit can be considered to be its' own series circuit. (They just happen to share a common power supply.) If you wanted to have only one current limiting resistor for both LED's, this would be a different proposition. In this case, you could still use the calculator for a single LED, but I would give the forward voltage of the lowest rated LED and, of course, you would want to add the total forward current of both LED's to get the total. Also, you might end up with issues if the flashing LED draws less current in the off state.
Since resistors are cheap and small, I'd go with the arrangement that you've got and just calculate the necessary limiting resistor for each LED.
As for suppliers, you might try Mouser. (Australian site link) They don't seem to have a warehouse in Australia, but they do have one in Hong Kong. They're based here in Texas, and I've used them for decades for parts on both personal and professional projects.
 

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