Charlie Kim's eeZ LED Takes All the Guesswork Out of Dialing in Your LEDs' Brightness
Insert LED, find your ideal brightness, and the eeZ LED tells you exactly what resistor you're going to need.
Maker Charlie Kim is looking to take the guesswork out of dialing in the luminosity of a given light-emitting diode (LED), by turning complex calculations and continuous trial and error into a simple handheld gadget: the eeZ LED.
"LEDs are annoying," Kim explains of the problem to be solved. "5mA is very different from LED to LED. What works for one LED doesn't work for another. But [the] goal isn't to calculate the current but to actually get the brightness you want. None of the calculations give you empirical results. Each situation demands a different approach. Whether it's a UI [User Interface] or perhaps some indicators inside an enclosure, you're trying to ensure visibility in bright environments. I'm sure you've seen examples of non-ideal implementation. Have you ever tried to explain how to calculate this to a non engineer? I'm sure there are makers, artists and hobbyists that would love an easier way."
That "easier way:" a dedicated luminosity tuner, which lets you manually adjust the brightness of any given LED and returns the value of current-limiting resistor you'll need for a given input voltage to hit the same brightness once the LED is in the final circuit. In short: it takes all the thinking out of tuning an LED, delivering exactly what you need for your desired brightness level — no calculations required on your part.
An initial prototype used the Analog Devices LT3085 variable output voltage power supply as a dimming control, but Kim soon shifted to an in-house design to reduce the cost of the gadget. Thermal compensation is used to deliver a ±70 PPM error rate, with oversampling used to get 14-bit resolution from a 10-bit analog to digital converter (ADC) — an improvement from 35µA to 2.2µA. Once the brightness has been chosen, an on-board display shows the next-highest commonly-available 1% resistor value you'll need.
"There were so many things I learned along the way it's hard to list them all," Kim says of the project. "The design keeps improving and hope that one day it gets into the hands of people who can use it to simplify their LED design. The results are much better than I had originally intended and it really is a sum of many ideas I've had over the years."
More information, including a one-page manual, is available on Hackaday.io.