Cheap standalone usb microcontroller

[tooki]

@tooki, I found your comments fascinating.

I have a problem with classic CRT monitors due to an astigmatism in one eye,
if I focus just right on the monitor, driven by a PC with some windows open,
I can see windows floating in 3D. Added, what was otherwise a bland look
on monitors, a wonderful attribute.


Regards, Dana.

Oh wow, that's trippy! I gather, then, that LCD, plasma, and OLED don't cause you trouble?

Glad you enjoyed the comments, it's a fascinating field! I just hope I didn't come off as too big an Arschloch in them! 

[knotlogic]

Hi tooki! Thank you for your comments.  I was looking at playing with some of the Linear Tech LED drivers, and would have severely underestimated the PWM frequency to avoid flicker.

That lead me do do a bit of searching on the topic of LED flickering and human perception, and I came across this article at Digi-Key which references IEEE standard 1789-2015:

https://www.digikey.com/en/articles/techzone/2016/jan/how-new-flicker-recommendations-will-influence-led-lighting-design

It's interesting that it's not just the frequency, but the min and max levels that contribute to the issue, although in the case of LED dimming I would presume we usually switch between 0 and 100%.  Also that the "gold standard" might be a PWM frequency of > 3 MHz kHz.

(EDIT:  That should be 3 kHz, not 3 MHz.  I blame the lack of sleep.)

Are there parts more suitable for driving high power LEDs that are capable of good dimming range and high PWM frequency operation?  I had a look at some of the Linear Tech parts and while they claim dimming ratios of up to 5000:1, the trade off is very low PWM frequency: ~ 100 Hz.  Even taking a 1000:1 dimming ratio we'd still only have a PWM frequency of 500 Hz.  (The TLC 5940 maxes out at 120 mA.)


Anecdote:  I was at a restaurant the other day where they were using some probably cheap LED lighting.  The colours were very cold and uncomfortable to my eye, and what really hit me was when I moved my hand, I was just able to perceive a strobing effect.

[tooki]

Hi tooki! Thank you for your comments.  I was looking at playing with some of the Linear Tech LED drivers, and would have severely underestimated the PWM frequency to avoid flicker.

That lead me do do a bit of searching on the topic of LED flickering and human perception, and I came across this article at Digi-Key which references IEEE standard 1789-2015:

https://www.digikey.com/en/articles/techzone/2016/jan/how-new-flicker-recommendations-will-influence-led-lighting-design

That's an interesting read!

What I do find curious is that the standard says that to prevent biological effects, 3KHz is the "minimum allowable frequency for basic PWM-based dimming", completely coinciding with my own findings!

It's interesting that it's not just the frequency, but the min and max levels that contribute to the issue, although in the case of LED dimming I would presume we usually switch between 0 and 100%.  Also that the "gold standard" might be a PWM frequency of > 3 MHz.

Where'd you see 3MHz mentioned there?
 But yeah, with LED, we're always just doing on and off, with only the effects of the switching speed of MOSFETs causing any values in between.

Are there parts more suitable for driving high power LEDs that are capable of good dimming range and high PWM frequency operation?  I had a look at some of the Linear Tech parts and while they claim dimming ratios of up to 5000:1, the trade off is very low PWM frequency: ~ 100 Hz.  Even taking a 1000:1 dimming ratio we'd still only have a PWM frequency of 500 Hz.  (The TLC 5940 maxes out at 120 mA.)

I've actually been wondering this myself. One option is to use a constant-current LED driver like the TPS92510 mentioned in the article, which if I am understanding correctly, accepts a PWM input and produces a smooth constant-current output. (The switching frequency mentioned there is not the PWM frequency.)

I've also been meaning to experiment with somehow driving power MOSFETs from the TLC5940. If anyone has any experience with this, please mention it!

Anecdote:  I was at a restaurant the other day where they were using some probably cheap LED lighting.  The colours were very cold and uncomfortable to my eye, and what really hit me was when I moved my hand, I was just able to perceive a strobing effect.

Yep, early and/or cheap LED lighting has terrible color rendition, and is often paired with terrible dimmers that cause strobing and flicker.

[knotlogic]

What I do find curious is that the standard says that to prevent biological effects, 3KHz is the "minimum allowable frequency for basic PWM-based dimming", completely coinciding with my own findings!

It's interesting that it's not just the frequency, but the min and max levels that contribute to the issue, although in the case of LED dimming I would presume we usually switch between 0 and 100%.  Also that the "gold standard" might be a PWM frequency of > 3 MHz.

Where'd you see 3MHz mentioned there?
 But yeah, with LED, we're always just doing on and off, with only the effects of the switching speed of MOSFETs causing any values in between.

Doh!  My bad!   That should be 3 kHz  I was short of sleep when I read/wrote that and misread 3000 Hz as 3000 kHz.  It's been bugging me and I was going to go back and reread it.

Sadly going between 0 and 100% is the worst case for flicker effects.

Are there parts more suitable for driving high power LEDs that are capable of good dimming range and high PWM frequency operation?  I had a look at some of the Linear Tech parts and while they claim dimming ratios of up to 5000:1, the trade off is very low PWM frequency: ~ 100 Hz.  Even taking a 1000:1 dimming ratio we'd still only have a PWM frequency of 500 Hz.  (The TLC 5940 maxes out at 120 mA.)

I've actually been wondering this myself. One option is to use a constant-current LED driver like the TPS92510 mentioned in the article, which if I am understanding correctly, accepts a PWM input and produces a smooth constant-current output. (The switching frequency mentioned there is not the PWM frequency.)

I've also been meaning to experiment with somehow driving power MOSFETs from the TLC5940. If anyone has any experience with this, please mention it!

I *think* some of the Linear Tech parts support PWM and analog (0-5V control) dimming at the same time but I'm not sure.  An input PWM signal results in PWM on the output, and the analog control can be used to adjust the current output setpoint.

The issue with adjusting output intensity by changing the current is it apparently causes a shift in colour temperature.  I've not tried it myself so I don't know how significant an effect this is, though I have in the past read accounts of people severely overdriving the early Luxeon devices and seeing a definite shift to blue.

Driving power MOSFETs from the TLC5940?  Sounds interesting.  Would this be as a switch in series with the LED?  Some of the LT parts (LT3518, LT3755) include this feature - that's how they do dimming.  I think there's something in the datasheet about syncing the PWM frequency with the switching frequency of the DC/DC converter.