[sdiy] Improving LED response when driven from half-wave rectifier

[KA4HJH]

On Sep 5, 2012, at 5:57 PM, Tim Ressel wrote:

> Exponential?  Sorry, but that didn't sound right. After all, power increases linearly with current, and light output is power, yes?
> 
> I checked datasheets from Kingbright and Avago and they both show luminous intensity increasing linearly with current.

I'm sorry, I've gotten things mixed up.

What I'm referring to is the response of human vision, which is non-linear. If you use exponential conversion, the LED will *appear* to be fading in and out in a more linear fashion. I've used the old reverse-biased LED pair myself in the past and I wasn't satisfied as they always seem to spend most of the time being brighter than 50%.

The expo table technique is one of the examples in the Arduino Cookbook and it works like a charm. The difference is amazing and definitely an improvement. It would be wonderful if there were some simple analog method for doing this as it gives much better visual feedback. 


I figured while we were going over every which way to do this I might as well add to the pile...


Terry Bowman, KA4HJH
"The Mac Doctor"