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Comment by guitarbill | Hacker News Reader

This is cool. Is the candle-flicker gif based on the algorithm, or the actual output from the LED? Because I assume the LED will smooth out some features. Vice versa, the LED probably needs to be driven with different data to produce the equivalent brightness variation.

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LEDs are extremely fast. The LED itself will add no perceptible smoothing. You could easily add a capacitor for low-pass filtering, but that would add cost so it's unlikely to be done.

They're fast until you start trying to use them to transmit data at a few tens of megabits/s.

Laser diodes, on the other hand, are fast

What does this have to do with anything?

It's a different perspective, I've spent a significant amount of time working with LEDs in a context where the rise time is important, and the fact that LEDs are slow (in this context) provided a significant challenge.

I guess the phrase "LEDs are extremely fast" struck me the same way a pedestrian telling you "walking is the fastest way to get around" when you're stopped at a red light in a Lamborghini would

"Extremely fast" doesn't have any absolute definition. We were talking about human visual perception, so "fast" in this context could reasonably mean "fast enough to have no visible smoothing". A typical LED is much faster than that, so in the context of fake candles I think "extremely fast" is fair. In the context of data transmission it would mean something else.

Yeah I understand it's entirely relative. I made that comment based on my immediate reaction. Compared to an incandescent bulb, LEDs are like the Lamborghini in my analogy

I love how LEDs can flicker extremely quickly. Back in the early 90s when I was working on HIPPI[1] network hardware, our crossbar switch had a 7-segment LED display on each port that indicated the current destination. These LEDs were actually updated synchronously. which worked surprisingly well as a debug tool. You could send to multiple ports and see the port numbers blended on top of each other in proportion to each ports data rate.

Years later, it seems blinkenlights[2] went out of fashion and everybody started quantizing blink rates to 1s or 0.5s max. /sigh/ it's throwing out useful information for no good reason.

[1] https://en.wikipedia.org/wiki/HIPPI

[2] http://www.catb.org/jargon/html/B/blinkenlights.html

I think quantized blink rates showed up around the time someone discovered that rx/tx leds as usually implemented on dialup modems of the time leaked data including passwords to anyone who could see the front panel.

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