Fenix TK40 - PWM dimming

Hi,

I wonder if anyone else has noticed that the Fenix TK40 uses PWM in low mode? I couldn't see any PWM in any of the other modes however.

I don't remember reading this anywhere on the forum.

zipplet said:

Hi,

I wonder if anyone else has noticed that the Fenix TK40 uses PWM in low mode? I couldn't see any PWM in any of the other modes however.

I don't remember reading this anywhere on the forum.

Click to expand...

That is probably because it does not use pwm. It has absolutely no pwm in the output.

That's what I thought. But switch the TK40 onto low and wave it around quickly (in a bright room so you can look at the emitter without hurting your eyes).

zipplet said:

That's what I thought. But switch the TK40 onto low and wave it around quickly (in a bright room so you can look at the emitter without hurting your eyes).

Click to expand...

I uses a oscilloscope and a opto sensor that can show pwm with frequency up to about 100 kHz and I can not measure anything, it only shows a horizontal line for the light output.

Hmm, strange that mine does it in that case. I'll see if I can capture it in a video I'll also try alkalines incase something is off with the NiMH batteries I'm using.

I've done some further testing and there is a bug in the firmware!

If you switch on the light to a mode other than low, and then cycle modes to get to low there is *no* PWM at all. However, if you set the light to low, switch it off and then switch it back on the PWM is visible.

If you have time, please try this and let me know what happens with your TK40.

zipplet said:

I've done some further testing and there is a bug in the firmware!

If you switch on the light to a mode other than low, and then cycle modes to get to low there is *no* PWM at all. However, if you set the light to low, switch it off and then switch it back on the PWM is visible.

If you have time, please try this and let me know what happens with your TK40.

Click to expand...

Nice catch, it is not really pwm, but some regulation artifact and on mine it is at about 470 Hz.

Thanks for checking that, I don't have a scope or sensor . Interesting scope plot :twothumbs

zipplet said:

Thanks for checking that, I don't have a scope or sensor . Interesting scope plot :twothumbs

Click to expand...

The interesting thing is, does this frequency vary with battery voltage? I am not going to check that today.

zipplet said:

I've done some further testing and there is a bug in the firmware!

If you switch on the light to a mode other than low, and then cycle modes to get to low there is *no* PWM at all. However, if you set the light to low, switch it off and then switch it back on the PWM is visible.

If you have time, please try this and let me know what happens with your TK40.

Click to expand...

Mine does the same thing. Never noticed it though until you pointed it out.

I only noticed it because I was comparing it side by side with another light that did have PWM using a desk fan. I do agree that it's barely noticeable as it's fast and at a low brightness. It should not be a show stopper for anyone buying this light.

In my dark bedroom I pointed the TK40 at the revolving ceiling fan and switched it on and off, cycled through the levels but could not notice any difference. :thinking:

Fan might be rotating too slowly. Set your TK40 to low. Switch it off, then on and wave it quickly while looking into the emitter (do this in a bright room so you dont hurt your eyes)

At its max speed the fan is very fast indeed and for instance the difference between L0D and LD01 is dramatic.

I have however done what you suggest in a bright room still to no avail.

Maybe we need more opinions.

Interesting. If you're certain your light has no flickering when you follow that exact sequence of steps and wave it very quickly then that means there are possibly 2 batches of circuits (or 2 versions of firmware)

FWIW I got mine from fenixtorch.co.uk a week ago (I usually use fenix-store but wanted it ASAP and w/o customs charges).

This ceiling fan has been my PWM yardstick for the last few years.

I got the TK40 from QualityFlashlights on April 10th so mine is a very early specimen.

I have been doing some more test, i.e. running a set of batteries down and checking the low level.
The frequency goes down to 400 Hz and might show up in other levels, when the batteries are nearly extinct, at other frequencies (I have seen about 600 hz).

Has anybody tested if they can see the frequency in the real world, i.e. does it freeze raindrops or falling snow?

And I can also rapport that the light get to hot to hold, at the head, when running at full blast placed on a table, but it takes more than 30 minutes.