D.I.Y. Illuminated Tailcap - gChart Editions

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Not that I can see. I suspect that, on NiMh, the driver is not leaking enough current to run the tail circuit. I bet a bleeder resistor would fix the issue. I might try that since it looks like the v1.0 might work in this light.

I’ve got a new tailcap design with consistent brightness and LVP with minimal additional components. Brief post and video demo about it here, I’ll do a write-up shortly.

you are genius Gabe.

I finally managed to solder the parts for V1.4 from scratch and it work :slight_smile:

That’s great, Nick! Did you use reflow for the boost side, or an iron? I would imagine it’d be extremely difficult with an iron on that WSON package. Using solder paste and a hotplate (or even a skillet) is pretty do-able.

Low-Voltage Protection, Constant Brightness

This board uses a Voltage Reset Monitor to provide LVP and an LDO to provide a constant voltage (an in effect, constant current). Everything is on a single side for quick & easy reflow soldering. It’s dual-channel, but includes a Bridge pad for making it single-channel.

  • LVP: MAX809SQ293D1T1G, a 2.93V active-low Voltage Reset Monitor with 0.5uA quiescent current
  • LDO: NCP553SQ30T1G, a 3V “NoCap” LDO with a 2.8uA quiescent current (typical)
  • FET: PFET, size SC-70 / SOT-323 (such as BSS209PWH6327XTSA1) or NTS2101PT1G
  • LEDs: 0805 size
  • Resistors: 0603 size

So altogether, there should be a total quiescent current of around 3.3uA while the tailcap is lit, going down to 0.5uA after LVP trips. In comparison to the current for the LEDs (typically 0.15mA = 150uA or higher, this is absolutely minimal)

Standard (16mm): Oshpark

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Big Switch (19mm): Oshpark (warning - the 19mm doesn’t have reverse polarity protection!)

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Testing video:

Such exciting stuff going on here. I have all the stuff to build you latest design (before the above), but big lights have been winning out on my attention for some time now. Looking forward to building some of your awesome tail lights eventually. Thank you for sharing your designs and expertise with us. :)

Wow. We are in the age of Constant Current lighted tail caps with boost circuit and LVP. Who woulda thought we’d ever be here? :open_mouth:

Hey Gabe

i reflow with solder paste :slight_smile:

With iron it’s impossible to do :open_mouth: . I tried couple of ways but it’s way too small the legs end up short circuit so i gave up.

Now im in love with AA flashlights :crown:

thumbs up to you

BTW, I just noticed that they’re back in stock in the Lumintop AE store for $17.51 with free ePacket

Thanks gchart!

I had a bit o’ fun tonight with a new tailcap: my first “smart” tailcap. It’s definitely not a new idea, PD68 was toying with this 3 years ago!

It’s using an ATtiny416 for the smarts side of things, driving 8 individual channels. To keep the power low, it checks the voltage, sets the LEDs, then goes to sleep. For testing, I have it waking up once per second. In a light, I’ll probably have it wake up once an hour or so. Just because there’s an abundance of flash for this use (4K), I added a basic startup animation: spinning circle, looped 3 times. Even with that, it compiles at only like 700 bytes or so.

I could probably do a little adjusting to the voltage on-off levels, but not bad for my first test. By some miracle, this was the first time I ever flashed the 416, and my first time writing code for it. It all came together pretty well.

Here’s the boards on OshPark. This is a small update from what is shown in the video. I’m using a P-FET for reverse polarity protection. I realized that I had two of the legs swapped on my initial design, so I just bypassed the FET pads for testing. This v1.1 has that corrected. Also not that I have not tested this in a complete light that might detract from the functionality. I’ll update this when I complete that test.- Ok, the first in-flashlight test is complete; see post 95.

Edit: BOM

Wow keeeewwww

Can u post the parts to built :slight_smile:

I like. It’s fun to think I have a sort of legacy here.

the question would be if its running on a bleeder or needs some intelligent driver that connects battery+ with a FET when off
bleeder and MCU running might get even with 470Ohm too much drop to get a real voltage reading, or even power up as voltage drops

I had same problem with my comparator tail cap and too high current draws in the >1mA range, rund fine on PSU but with bleeder you got no real voltage reading as too high drop on bleeder

Great to see you on, PD!

Oh, and BOM added to the post

Thats a great question. My plan is to have it running on a bleeder, but I have not tested that yet (so keep that in mind before ordering parts, if someone is so inclined). I might have to make tweaks based on how it acts behind a bleeder.

Nice job gchart!
Especially like the decreasing lighted led’s to battery level indicator. :+1:

SUPER COOL!

Seems like with probably just a few very minor code changes you could use half green and half red LEDs and have a tail ring that fades from green to yellow to red.

The problem with fading is that requires ramping PWM up and down, which requires the MCU to be awake. Awake, the 416 will probably use 1mA (@3.3MHz). Asleep, it should be around 1uA. (datasheet pages 439 and 445, not my measured values). If battery drain isn’t too big of a concern, that definitely is a possibility!

Ok… I tested it in-flashlight. It’s a Convoy M1 with a Nanjg105c & 750 Ohm bleeder. Results seem mostly positive.

Firstly, it works. But a few observations:

  • I’ll definitely need to adjust the voltage detection levels. A 4.09V battery gave 6/8 LEDs. A 3.54V battery gave 3/8 LEDs.
  • The LEDs are dim during the animation, I’m guessing because the MCU is taking up most of the current. Not a big deal. I might even remove the animation. Not sure yet.
  • The first voltage check reads low. This is despite the fact that I take 16 ADC readings and trash them, then grab 8 readings and average them. I guess it’s just because it’s taking the reading on the coat tails of the animation? Dunno, I can probably code around it.
  • I can probably reduce the MCU current draw in active mode (ie, animation) by reducing the CPU frequency and making sure I have some other things disabled (like BOD). Freq is currently 3.3MHz, I think. I just rolled with the default, which I think is 20MHz with a divider of 6. Any idea whats a safe, low frequency to use?