The Whispering Gallery - Modified Category - 7th Annual BLF/OL contest entry

I love AAA flashlights.

This is a Thrunite Ti3 V2.

I like a lot of things about it except that it has next mode memory. Initially I thought that the next mode memory only lasted a minute or so, which wouldn’t be so bad. But sometimes it would last longer than that, and sometimes it would come on in low after just a few seconds. I wondered if the length of time that the next mode is remembered was dependent on the on time, as if the capacitor takes some time to charge up and then have a longer memory. (Full disclosure, I have no background in electronics).

I did a test where I turned the light on in low for varying lengths of time, and then waited varying lengths of time before turning it back on. In between tests, I waited at least 1 hour. This took a few weeks to complete.

I still don’t know why the behavior of this light is unpredictable and would love some insight from the experts here.

Here is the driver. I pushed it out of the pill with a cotton swab after desoldering the LED MCPCB. The red arrow points to a piece I broke off of a component in the process (an inductor?). I don’t think it is a problem.

Then, I used a pencil to draw lines on capacitors to see if that would shorten the length of the NMM. The red arrow points to the one that worked. With the line, the NMM seemed to last pretty consistently ~10 s. Odd to observe predictable behavior after starting with something so unpredictable.

Testing with alligator clip wires.

The next step will be to solder a resistor on that capacitor, testing to find the optimal resistance. I now have 1800 size 1608 metric resistors ranging from 10 Ohm to 1 megaohm. The first and hopefully not last giveaway in this thread will be my extra resistors.


Welcome to the comp whispering :slight_smile:

Next mode memory would have to be one of the worst ideas in the history of flashlights :confounded: So good choice of mod :+1:

Welcome to the party The Whispering. :slight_smile:
I hate NMM so much…I agree with pinkpanda, this is a nice choice.

The old pencil on capacitor trick, nice :wink:
Good deduction, perseverance testing and showing results of the NMM times too :+1:
Looks like a big bag of resistors from FT, always come in handy.

Nice. NMM is a deal breaker.

Well… Confession time. My DQG Slim AA has NMM sometimes. It’s pretty unpredictable on mine. But I put up with it because it’s so otherwise nearly perfect.

Thanks all for the kind words. I should clarify that I’m well aware that I didn’t invent the pencil trick, but I’ve never seen it done on a Ti3 V2 so I thought it was worth posting about.

Hopefully going to do a few other things to this light besides fixing the NMM…we will see how it goes.

I have now tested several resistors soldered over the capacitor that I suspect is responsible for the NMM. By the end, I got better at the soldering. These things are really small.

After trying a couple of resistors and testing using the test wires, I got NMM length of ~6 seconds with a 100 kohm resistor. Great! So I reassembled the light. But the NMM was lasting longer when assembled, ~17 seconds. I’m still not sure if this is a real difference, or how to explain it. At some point, I realized that I could assemble the driver/pill/MCPCB and that the wires were long enough to still access the driver, so I didn’t have to use the test wires like I showed in the first post.

So I tried more resistors, trying to tune the NMM to a desirable length of ~5 seconds. Unfortunately, it seemed like I was getting diminishing returns, and the light when assembled never went below NMM of ~11 seconds. The NMMs with a resistor on the capacitor were generally very repeatable, and I tested each resistor several times. Here is a table of the results.

At this point, I’ve started working with my brother, who is an expert in electronics and such. He made some assumptions about the circuit, and then did some circuit simulations, but couldn’t replicate the results that I was getting. One of the oddest parts is the capacitor discharge time, which can be easily calculated. Even if the only parallel resistance is one of the resistors that I tested, and the capacitance is the highest possible for 0603 package (which I believe is 47 uF), the capacitor is generally discharged long before the NMMs that I observed. This is true if the capacitor is charged to 1.5V battery voltage, or by the boost converter to ~3V.

Maybe some of the assumptions about this circuit aren’t true though. So I bought my brother a new Thrunite Ti3 V2 from Amazon to look at (since he lives on the other side of the country). He found that the NMM only lasts ~10 seconds though, unlike my example. However, it goes into strobe seemingly randomly. The mode sequence is supposed to be L-M-H-L-M-H-S, but his light often goes into strobe straight from low or medium.

That’s all for now. We are going to try to learn more and figure out what can be done.

Interesting mod The Whispering. You are certainly doing a lot of experimenting to get rid of an old Chinese favourite. :beer:

Welcome ” The Whispering ” to the fun. :beer:
You certainly are experienced at modding lights, nice explanations of your operations. :+1:

Thanks to you both. I wouldn’t say I’m all that experienced…especially compared to some of the amazing projects done by BLF members. I’ve enjoyed reading through the other threads in this contest, including both of yours. Just trying to learn and have fun with this :smiley:

I hope you can figure this out The Whispering. So does it seem the pencil trick had the best results so far? My Astrolux A01 has similar behavior, but much longer off time. I give it a pass though due to it’s Nichia 219B.

Ok, the next thing I did was solder some wires on the capacitor so that I could measure the voltage across the capacitor when the light is on. I found that it varied from about 2.4-2.7V depending on the mode. The capacitor is charged by the boost converter, so low mode gives the lowest voltage and high mode give the highest voltage.

After some discussions with my brother, I made some rough assumptions that the minimum voltage to power the MCU is ~0.6V, and that it uses on the order of uA. At this point we don’t know the capacitance of this capacitor either, so I made the table below to show the expected length of NMM for various capacitors and parallel resistance (the resistor which I soldered onto the capacitor). 50 uF is about the max capacitance for a 1608 capacitor, and 1E6 kohm represents the unmodified flashlight where only a few uA are drawn by the MCU. I defined NMM length as the time for the capacitor to discharge from 2.4V to 0.6V. The equation is Vc=Vo*e^(-t/RC), where Vc is the capacitor voltage at time, t, Vo is the initial voltage, R is resistance, and C is the capacitance.

The problem is that this doesn’t match any of the behavior that I observed, namely that I was getting NMM lengths of >10s even with the 1 kohm resistor. So I concluded that I’ve been working with the wrong capacitor, and started trying the others.

This one turned out to be the right one. I drew a pencil line first, and then cleaned it off and soldered on some wires to check the voltage, which was also about 2.4-2.7V. Then soldered on a 1 Mohm resistor (the highest that I have), and the NMM was ~3s.

Based on the assumptions used to generate the NMM table, the capacitance of this capacitor is calculated to be ~2 uF.

I was happy with these results, so I decided to reassemble the light.

Good to see it working. Your persistence is impressive. :slight_smile:


I first had to do something about the inductor that I damaged, so I put on a little bit of this MG Chemicals 832 HD potting compound with a toothpick.

Then I used my reflow station to install a Nichia 219b 3500k R9080 LED, and reassembled the driver, pill, and MCPCB.

Added some commemorative laser marking for the 7th Old Lumens contest, and took a quick beam shot next to my Ti3 titanium with 219b 4500k R9080 (which has the new shorter and fatter V2 body and came with only 10s NMM and works flawlessly). Both LEDs look great in real life.

Here is a close-up of the laser marking. Mine didn’t come out quite as sharp as that done by Thrunite.

Edit 2/28/20:
To put some data to it and check the consistency of the NMM length, I did 10 tests each of two different off times. Unlike the original light, which had seemingly random NMM times tested up to 10 min (shown in the first post), after the resistor mod I found the behavior to be repeatable.

I consider this light to be complete. I’m going to use it for a little while to make sure that there are no issues and then post a giveaway for it. My brother has also reverse engineered the circuit now and I will post that information soon.

It’s been an honor to participate in this contest. Congratulations to all the other participants on their excellent builds and modifications.

Congrats on finishing :partying_face: The laser treatment is a nice touch :+1:

:+1: :beer:

Good presentation :+1:
That really helps us to understand the detail operations going on inside a driver. :+1:
Great Finish with the laser :wink:

Nice work The Whispering. Nothing like a custom light to suit your own needs. :beer: