BLF A6 FET+7135 Light Troubleshooting and Mod thread

I don’t envy you, trying to put all the useful info in one place.

But I’m glad you’re doing it! :slight_smile:

Is there any solution for pitchi sound on Hi modes, my is just too loud, even my kid standing 10 feet from me asked me what is that noise. I know kids can hear better then us hi frec. but i can hear it too. Its only when current is regulated, so 5th and 6th mode, or 3th in 4 mode configuration.
Thanks
Nikola

If it has a high-pitched whine, there is probably something wrong with the light. It should be generating sound… but it’s pulsing at 19 kHz which should be too high for almost anyone to hear. However, if the driver is under-clocked or there’s a weird connection making resonance, it could be making different frequencies.

If you put the light in bike flasher mode, it should stutter once per second. But if the driver is under-clocked, it would then stutter slower, like once every 2 seconds or 4 seconds. I’d suggest testing this first before opening the light to look for anything else which might be weird.

Yes its stutter once per second, maybe it just bad solder like from the picture above, I will try to reflow. Also might be that all one have this but no one have noticed. Just put the light closer to the ear and check it out ?

I’ve heard that too but not every time. I’m gonna put a fresh cell in the one I went through and see because I felt like it was when pushing high amps.

Haha thanks TK please if there is any thing you want on here let me know. I still really don’t understand the in and out of why this resistor here and this size resistor there. You and wight (who am I missing. db?) seem like the pros!

I definitely am getting a squeal in modes 5 and 6 on both of my lights.

So it just so happens today that I am working on a sound proof booth here at CSU. Lucky me the doctor in charge of this is studying how auditory signals affect brain waves. :slight_smile: We got to talking about khz so I brought up the 19 khz TK had mentioned. He said that while most people cannot hear that pitch - some nice sound systems are designed to reproduce up to 20k just in case I can’t remember the number he threw out but some people can get up there with good ears. Also he explained that like trying to talk under water you can hear but the water really puts a damper on the frequencies.

So what I got out of it is the metal or something around the driver is being resonated at a pitch we can hear. My thought is something is echoing the 19k at a slower rate like the capacitor or a mixture of things bouncing little sine waves around at a different rate?

One more thing I have noticed and mentioned before,is that head is not waterproof,glass is sitting directly on metal,and no O-ring between. . . so dont put it in the watter couse led is almost directly exposed

Well with a thread like this started, you may also be be one of the pro’s shortly!

Seriously good thread here, should be stickied….

I was thinking the same thing. Perhaps a thin o-ring can be added between the bezel and lens.

No I have tried that but then you cant screw the head to the end…

I see your point but in the end I kept mine between the lens and bezel. And very gently threaded it all back together as not to pop the o ring crooked. Some of my next pics are about the accidental dedomes happening.

Thanks Reman! I fell in love with this site immediately. I really just wanted to give back in some way after all the kindness that has been shown to me. And seeing as I’m new I have directed some things toward the others that are new but wanted this light. As I keep repeating it’s really not just the lights! It’s the people here that make it great!

In theory, it should be 18.75 kHz, because that’s the speed of PWM on the attiny13a. 4.8 MHz / 256 ticks per cycle = 18.75 kHz.

In practice, the speed varies on each unit by up to 10% or so. It could end up anywhere from 16.9 kHz to 20.6 kHz.

… and then there’s resonance to account for. PWM makes a square wave, which has more harmonic frequencies than almost any other kind of waveform. Viewed in a spectral manner, a sine wave looks like a flat line… but a square wave looks more like a vivid sunset.

To hear the 19 kHz tone, point the light at a black microfiber fabric from very close, and hold your ear or a microphone very close too. The photoacoustic effect should produce small sound waves as the fabric rapidly heats and cools. With slower PWM, the light can even be programmed to play songs this way. I’ve been tempted to make an infrared laser specifically for this purpose, so I can point it at things and turn remote objects into speakers. Then again, I might also end up starting fires.

Other parts of the light can make sound too, as current rapidly increases and decreases. The springs are one likely culprit, since they’re a big source of resistance and they’re prone to ringing anyway.

Even with the high PWM, I hear a whine on medium modes quite often in lights I mod. Most times the sound is coming from the tailcap. Either the spring, the switch, or the tailcap to battery tube connection itself. There have been a few instances when I have not been able to get rid of it no matter how hard I tried.

BTW, these drivers can be run faster to speed up the PWM… The problem is, the more pulses per second, the more time the waveform spends rising and falling. This makes the light less efficient and more voltage-sensitive. Comfychair and I both measured this a while back, me with some improvised tools, comfy with an actual oscilloscope, and we got roughly the same answer: At the time scale of a millionth of a second or faster, the leading and trailing edge of each pulse become pretty significant — sometimes enough to outweigh the rest of the pulse.

For example, a FET-only driver can’t get a proper moon mode at 19kHz because each pulse (at fast PWM=0) is only half a nanosecond, and the actual output varies from ~3.0 lm to ~0.001 lm depending on the battery voltage. It never reaches a full “on” state, so the question becomes how high the pulse can go in that time. A single 7135 chip fares much better, because it can use longer pulses to achieve the same total volume. It’s still voltage-sensitive, but the output only varies from like 0.6 lm to 0.4 lm.

At the other end of the spectrum, slow PWM makes the output very stable, but it also introduces audible sounds and visible strobing.

So, we generally aim for the slowest speed which will be neither visible nor audible, meaning about 20 kHz.

On the tiny25/45/85 series, this will be 25kHz or 31kHz, but I haven’t tried it enough yet to figure out where the sweet spot is.

PWM on moon mode is only visible with close up shot . Thanks Toykeeper for nice explanation :slight_smile:

TK, I’m not convinced that running them higher will completely solve the problem. It seems like the high frequency is somehow causing certain parts to vibrate at a lower frequency. My S8 is normally silent, but if I loosen the tailcap the tiniest amount a faint tone can be heard. If my dog whistle app is to be believed, that tone is around 13-15khz. The problem seems to manifest itself much more in FET drivers than linear drivers. Adding more solder to connection points like switch tabs usually helps.

Awesome tips pilotdog68!
Could almost start a thread on eliminating flashlight PWM harmonics.
Great info like this often gets buried in the vast knowledge of BLF threads way too fast.

There you go! I was hoping the great minds of blf would show up here! :party:

Moon runs at half the usual PWM speed, about 9 kHz instead of 19 kHz. It uses a slower setting to improve the stability and reduce voltage sensitivity. And at such a low output level, the 9 kHz tone it makes should be fairly hard to hear.

FET-based modes are louder because there’s a lot more current pulsing. 350mA vs 5000mA, roughly, so it’s like turning the volume up by a factor of 14.