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Balancing the LEDs with Resistors

A project log for Pumpkin Light

Just a simple project to illuminate a pumpkin on a windy day.

petri-varsaPetri Varsa 11/09/2014 at 13:520 Comments

One issue I had with the light in its current state was that the "orange" LEDs were much dimmer than the RGB LED, so the flicker wasn't as noticeable as I wanted. The other issue I had was that the RGB LED seemed out of balance. Red was too bright, and green was too dim. The cyan looked too blue, and the yellow looked more like orange. So I decided to adjust the various brightnesses using different resistors.

I started by cleaning up my breadboard a bit. I routed all the digital lines to one side, put the LEDs on the other side, grounding them all on the rail, and then used the resistors to jump the columns. Unfortunately, I was unable to find the packaging that came with my "orange" LEDs, so I don't know what voltage they can handle. (I quotate the "orange" because I think they are really red LEDs in an orange lens.) I only supply 3V to the controller, and with some experimentation it seems as though those LEDs take 3V no problem. So I just pulled out those resistors and now the flickering is much brighter.

I then set off to balance the RGB LED. First I make-shifted a diffuser. The discarded nip from a calking tube seemed to work well. then I just played with various resistors until I found a combination that seemed balanced. I ended up using 260 Ohms for red, 180 Ohms for green, and 220 Ohms for blue.

One issue I still have, that maybe I don't fix, is that the flickering orange LEDs make the RGB LED flicker too. So to balance the RGB LED, I needed to pull the wires out of the orange LEDs. Otherwise I wouldn't get even illumination. I reconnected the orange LED signal lines once the RGB LED was balanced. I suspect the issue is current. I probably don't have enough current to supply a constant power to the RGB led when the orange LEDs are flickering. I thought maybe I could smooth out the power to RGB LED supply lines with a capacitor, but that didn't seem to work. I tried various Faraday values, but the LEDs wouldn't illuminate with a cap in series. Maybe parallel is the correct way to wire it? My analog electronics skills are obviously close to zero. I want to fix this for education purposes, and because I'm a perfectionist that way; but even if I did I would probably not implement the fix in the final version because there isn't much room in my final project enclosure for the extra parts.

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