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Geek Culture / Brightness Lost By Fast Switching of LED

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Dark Java Dude 64
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Posted: 17th Jun 2011 23:59 Edited at: 18th Jun 2011 00:00
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So for the Programmable LED Light Show Thingy i mentioned i would be making earlier, i realized that to control 16 LED's i would need to switch each LED on and off as the LED's take turns being lit up (there would be a 16 byte buffer, each byte being the brightness of the corresponding LED, and i would need to toggle which address is being read as only one address can be read at a time), and i thought that this might decrease the brightness by quite a bit. Say each LED was switched on and off 60 times per second, how much would that lower the brightness?? Originally i thought i could use a capacitor in parallel with the LED to give the LED a somewhat constant current, but if i need an LED to suddenly become darker, a capacitor is no longer an option as it would make the LED fade to that lower brightness. As i think about it more, being that i live in the USA our lights switch on and off 60 times per second and they maintain a nice brightness.

So yah, would you think it would lower the brightness by much?

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Neuro Fuzzy
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Posted: 18th Jun 2011 02:58
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nope, it doesn't effect the brightness much - pulse width modulation is the standard way to go with that sort of stuff.


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Dark Java Dude 64
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Posted: 18th Jun 2011 05:01
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So adjusting pulse widths is what i shall do to control brightness? That seems like it would work rather well but each LED will have a brightness from 0 (off) to 255 (full on) and at lower brightness's, it would have to switch rather slowly, probably noticeably
Quote: "nope, it doesn't effect the brightness much"
That does answer my question so im happy.

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The Wilderbeast
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Posted: 18th Jun 2011 11:57
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PWM actually means that you can make it slightly brighter. The reason for this is that if you drive an LED slightly harder than it should go for a very short amount of time, then it increases in brightness (obviously) but also doesn't damage the LED.

Source? A friend of mine researched and used that technique for an A2 project - works brilliantly!


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Dark Java Dude 64
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Posted: 18th Jun 2011 12:25 Edited at: 18th Jun 2011 12:28
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IMO i dont think i would want to chance it...

Speaking of pushing an LED over its limits, last night i put a perfectly good blue LED through torture by passing 4.5 V through it; never seen an LED so bright! I dont know its rating as it came from a crappy thing i got at the Dollar Store that broke but the leads were getting rather hot. But the LED lives on today!!

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Interplanetary Funk
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Posted: 18th Jun 2011 12:31
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are you controlling the LED through 1 pin? cos if you had a 2 ports you could use transistors to determine which one was on and a basic resistor based ADC to determine the current going to the LED.

But if you're only using 1 pin then yeah, PWM.


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Code eater
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Posted: 18th Jun 2011 12:32
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What a trooper of an LED

If pots and pans were "if"s and "and"s there would be no work for programmer's hands...
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Dark Java Dude 64
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Posted: 18th Jun 2011 22:01 Edited at: 18th Jun 2011 22:18
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Hmmm... You made a good point, i shall be using two ports to control it! That's a more attractive method of controlling an LED to me

Edit:
So i have been looking at the place i usually look to find electronic components (even though i have never gotten any) because they allow you to get things without ordering two trillion of them; they are futurlec.com. But i found a nice DAC with a current settling speed of only 100 nanoseconds so i will likely connect all of the LED's grounds to its output and the LED's inputs each to its own transistor.

Quote: "What a trooper of an LED"
I feel bad for the little piece of epoxy coated semiconductor! I probably ate some of its efficiency by doing that But i have no use for it!

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