PWM - What is it, How does it work and how to detect it.

jeff51

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KITROBASKIN
Will do. For the shorter stuff, I’ll put it here.
I’d like to do some better videos showing the light as it’s ramping and the waveforms it’s using to control the brightness. I just need to figure out how to do it (!).

The post about making a setup to do the measuring will be pretty long. So I was thinking it might be better to branch off and do it separately.

All the Best,
Jeff
 

jon_slider

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The Videos:
This is the original Low Res Flicker video showing the Super Tiger headlamp and the Nitecore TUBE.
https://youtu.be/RyJUbe-foPM

This the HD version of the headlamp.
https://youtu.be/vlqVixQZgFs

And here is the Rayovac screaming at 12K and 64K.
https://youtu.be/V4otzemA744

I see them all, and the first two hurt my ears

I can't hear the Rayovac.. yay!

thanks for showing me another reason to avoid PWM
making plans NOT to listen to that noise again,
it makes me hostile.. LOL
 
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jeff51

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None of the lights, luckily, make any physical noise. A headlamp would be especially annoying if it started singing.
The cheap camping lantern dose make a little bit of noise but I have to hold it up to my ear to hear anything.

I have read that some folks do have lights that they can hear and it annoys them.
I wonder if it is poor design or perhaps improper component specs that contribute to singing lights?

All the best,
Jeff
 
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peter yetman

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I did my first the other day.
Did you use the "insert video" button, top right in the toolbar on the Quick reply Editor? You click this and enter the URL.
When you get back to the editoir it should show your URL with VIDEO in square brackets either end of the URL.
Post Quick Reply and you should see a picture box with your video in it.
I think that's about it.
P
 

archimedes

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xevious

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The only flashlight I still have where it's possible to hear inductor whine is on the NovaTac 120P, when running in a low enough mode to trigger PWM. But it's so incredibly faint to my ears, I'd only hear it if I kept the light within an inch of my right ear (left ear is somewhat damaged and tinnitus cancels out a lot of frequencies). Anything beyond that would annoy me. At this day & age of LED flashlight technology, it's pretty unacceptable for a maker to produce a light with audible noise or PWM. Just doesn't have to be that way, as so many makers have successfully avoided those unwanted pitfalls.
 

jon_slider

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Nm5voEt.png


EExYeHd.jpg
 
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Hondo

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I'm guessing you have "circuit warble" in your Mini. But it is a bit fast, or your swing a bit slow, to be certain. I was not aware of any other 4Sevens lights besides some of the high voltage Quark heads having this.
 

jon_slider

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I actually see dots when I swing the FourSeevens light, but the camera sees the blur I posted.

I know it is not PWM, the light uses Constant Current, or as I like to call it, Constant Flicker.. LOL

I did swing the Q123 as fast as I possibly could, in an attempt to get a photo that showed the dots that I see with my eyes, but what you see is what my iPhone captured.

My HDS produced dots when I waved it fast, I believe it IS using true PWM.. Though HDS claims they use a type of circuit they call Constant Power, yet another variant in the range of circuits that produce flicker.

My Olights also show blurred dots, like the Foursevens (maybe because Olight makes FourSevens branded lights)...

----
moving on past the Quarks..

An example of PWM from this post:
ARxi6efl.jpg
4UdUUG2l.jpg
 
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jeff51

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I just posted a way too long thread about using a computer and sound card to measure PWM.
Good night time reading for those needing to nodd off...

[FONT=Verdana,Arial,Tahoma,Calibri,Geneva,sans-serif]https://www.candlepowerforums.com/vb/showthread.php?461093-Measure-PWM-using-a-Computer&p=5330349#post5330349

All the Best,
Jeff
[/FONT]
 

DoctorMemory

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Tons of newer cars have LED’s for daylights and rear position lights. As we all know the very same rear position lights are often also used as brake lights, so these lights need to be dimmed to differentiate from when a driver applies the brakes. Some manufacturers –perhaps most?- use PWM to achieve this, but some of them use a very (or failry) low frequency of PWM that actually affects some people, like me. I believe there is a more and more urgent need to sensitise manufacturers as the effects can be very uncomfortable for the eyes of some people. Just as an example, when I drive at night behind some models of Cadillacs or Volvo’s, I either slow down drastically to let them out of my sight or pass them as fast as reasonable (sometimes over the local speed tolerance) because it tires my eyes badly.

I couldn't agree more. Thought I might be the only one that saw dashed red lines for taillights when moving my head.
 

jon_slider

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No they did not use PWM. Not one. They simply had 120Hz line ripple.
can you help explain the difference between PWM and Ripple, in practical terms?

1. does ripple create banding in photos, the way PWM does

2. does ripple cause visual trailing dots, when moving ones head... as happens with LED tail lights?
 
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