Pyra Prototype Videos - Askarus Edition

Hellfleck

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LEDs are current driven, and they have a forward voltage which below they will not light up - any kind of LC filter there is a bad, really bad idea, over current is a death sentence

you can use a fixed current source with pwm or an adjustable current source to regulate their brightness

pwm is thought of to be easier, more energy efficient and color stable

https://www.maximintegrated.com/en/app-notes/index.mvp/id/3256

LEDs do not have a linear current to light output curve and worse they change their color too

each LED technology is slightly different too btw.

http://central.oak.go.kr/journallist/journaldetail.do?article_seq=12166

but what I did not know before is that PWM dimming white LEDs (phosphor types) actually produces a shift in colors too xD

so yellow shifts for adjustable current sources and blue shifts for fixed current sources with PWM

I think normal monitor backlight run above 2000 Hz but at some point you will run into EMC problems .... so playing it safe for testing and giving users the ability to clock it up is a good solution I think
 

slaeshjag

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500 Hz is more of a hard limit in the backlight driver used. It's really nothing more than a boost converter in constant current mode. You can control it in two ways. One is to apply an analog voltage to the enable pin. The other is to PWM the enable pin. The latter is the mode used in the pyra. While the boost converter itself if running at hundreds of kiloherz if not over a megahertz, the startup/shutdown time of the regulator (since that's what the enable pin does, you're really just turning the entire boost converter on/off really fast) prevents you from PWM:ing it much faster.
 

levi

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Why do whe use such divicult technology??
What’s happens to the good old Lightbulb??
80 Wats should be enough to enlighten the Keyboard..
And strapped to a ~30Wh battery (8000mAh * 3.7V) that'll give you less than half an hour of runtime!

In other news, more videos will be coming I've heard. I don't know how many, but I also wouldn't hold your breath - I understand these two videos took long enough to get edited into shape, so cut the guys some slack.
 

neko

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but what I did not know before is that PWM dimming white LEDs (phosphor types) actually produces a shift in colors too xD

so yellow shifts for adjustable current sources and blue shifts for fixed current sources with PWM
The boost converter contains an inductor and it doesn't switch off immediately. So increasing the PWM frequency will end up driving the LED at a lower current for part of the cycle, and thus you get the yellowing effect.

LEDs are current driven, and they have a forward voltage which below they will not light up - any kind of LC filter there is a bad, really bad idea, over current is a death sentence
If you were to add inductance without capcitance, the inductive kick could kill the LED, or kill the boost converter transistor. This is why you need a capacitor in there to stabilize the voltage. The boost converter contains an inductor, but if the circuit is designed properly, it won't kill the LED.
 

BeMoreViking

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Nice videos. What do we think the chances are of having a finalized case before the folks in Greece go on break for the summer?
 

levi

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What are we actually waiting for in the cases? A tweak to the stylus holder is all I can recall. I'd say there's reasonable odds they'll have that changed in the moulds before the summer recess. Whether they'll get units pressed and out before they sit in courier's warehouses gently cooking all summer is another question though.
 

T.T.

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500 Hz is more of a hard limit in the backlight driver used. It's really nothing more than a boost converter in constant current mode. You can control it in two ways. One is to apply an analog voltage to the enable pin. The other is to PWM the enable pin. The latter is the mode used in the pyra. While the boost converter itself if running at hundreds of kiloherz if not over a megahertz, the startup/shutdown time of the regulator (since that's what the enable pin does, you're really just turning the entire boost converter on/off really fast) prevents you from PWM:ing it much faster.
So, instead of putting a filter on the output of the backlight driver, we'd be putting the filter on the output of the CPU and thus providing an analog voltage to the input of the driver? If that's the case, a low pass filter shouldn't be too hard since it doesn't have to handle much current. (presumably at least. Figuring these things out easier with a datasheet....)
 

neko

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So, instead of putting a filter on the output of the backlight driver, we'd be putting the filter on the output of the CPU and thus providing an analog voltage to the input of the driver? If that's the case, a low pass filter shouldn't be too hard since it doesn't have to handle much current. (presumably at least. Figuring these things out easier with a datasheet....)
The boost converter has an intrinsic inductance and capacitance, which acts as a low-pass filter if you increase the frequency enough. Alternatively, you can add an additional inductor and capacitor, and use a lower frequency. It ends up being roughly the same effect.

If using a high frequency interrupts the CPU, or creates noise, then it may be desirable to use a lower frequency, but then you need to add additional filtering, which increases the component count. And, as mentioned, if you have too much inductance without enough capacitors then it can make the voltage unstable, though I don't think this is as big of a problem as people have made it out to be.

It was also mentioned that some LEDs can shift color slightly when driven with a lower current, such that it will get more yellow when dimmed. This is (I think) due to saturating the phosphor at higher output. This isn't really a problem with most LEDs that I've seen, but I suppose it's possible. It would depend on the specific characteristics of the LED used.
 

EvilDragon

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I hope you can rest soon!
Me too :)
Lot's of video editing stuff going on, besides running the shop and working on the Pyra :)
But I'm catching up - and once the Pyra is out, I should have enough funds to hire someone in my shop :)
[doublepost=1523841633,1523838004][/doublepost]Next video online, see first post.
 

Djoga'Ro

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... once the Pyra is out, I should have enough funds to hire someone in my shop :)
[doublepost=1523841633,1523838004][/doublepost]Next video online, see first post.
Thought, Ascarus is working in the shop. Did I get that wrong or does he not count for some reason?
 
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