I poked and prodded at this a little bit, but not all that much so far, mostly because I can't make any sense of what I found. Can't ID the controller, and the pin layout is utterly alien.
There's no direct path to ground on ANY pin. Switch goes between two pins, no path to ground on either switch pin. I only followed the traces out to their first component. Dashed lines are traces on the battery side of the board.
Pin #1 goes to B+. Pin #3 goes to the LTSX e3 boost controller, but it is NOT, from anything I am able to measure, a PWM-ed signal.
No markings whatsoever on the top of the controller, hidden on the underside is 'OQ1313', which I can't find any relevant info on.
The driver in stock form, being a boost driver, will run a single MTG2 perfectly fine from only one cell... shame there's no room for that in the super-skinny head.
Good work so far. To make sure I understand what you are saying, your DMM does not show continuity between any of the U1 pads and GND?
Is this the chip we suspect LTSX E3 to be: LTC1871 ?
What is the voltage between Pin 1 (red) and Pin 8 (green)? EDIT: in other words, looks like a PIC to me if that voltage is appropriate.
EDIT2: So that’s the RUN pin on the LTC1871, looks like it’s being used as a shutdown pin here. Pulling that pin low (below 1.248v) should result in no light. Pulling it high should turn the light on. I do not immediately see how modes are handled.
None, zero, of the MCU pins go to ground. Ground's gotta be supplied by one of the other components only after switch-on, and then removing the ground to turn off.
Yes, LTSX chip is LTC1871. I'm hoping to ignore as much of the power side of the circuit as possible - that part works fine, it just needs a way to get a better UI in there. Checking it (MCU #3/LTSX 'RUN' pin) while powered up with the Hz scale on the DVOM shows 0Hz, it just changes the voltage for the different modes. I'm pretty confident that's accurate since the same check on pin #6 of an ATtiny shows Hz that correlates to the firmware version it's running (9kHz/19kHz).
I don't recall the voltages at the RUN pin; it was B+ or less, otherwise it would have been weird enough I would have written it down. I can resolder and test but I'd rather not if there's other things to check while it's still removed. If what I have on the diagram so far is enough and everything else can be done with it put back together that's no problem.
I also can't find a ground pin at the LTC1871; #6/GND does not go to ground. #10/'SENSE' pin goes to B+, #9/'Vin' does not.
Wait - this is a boost driver, with LED+ going to B+ (through the flyback diode & inductor), this thing boosts by running LED- at a negative voltage? What the hell is that about? What if the MCU #1, that goes to B+ is actually the ground, and the + supply is from a voltage boosted up above B+?
I’m not sure what else to check with it off. You’ve taken pics already. You can wait for the rest of the jury to come in, but I think biting the bullet and putting it back together is probably the next step.
Analog voltages coming out of a cheap MCU is pretty abnormal I think, that requires a DAC.
I’m with you on pulling LED- lower than BAT- in order to drive the LEDs from BAT+. The rest of what you said doesn’t really add up though, there’s no reason to drive an MCU in that way. As far as I know there are only 2 commonly used MCUs that could be in play: PIC and ATtiny. PIC meets the pinout I mentioned, ATtiny doesn’t. ATtiny also doesn’t match up with the crazy boost-circuit-drives-MCU-theory pad layout, so I think we can set that theory aside until measurements show it should be considered again.
There is a negative voltage application circuit in the datasheet. EDIT: nevermind, that’s not applicable here. Another look at the application circuits shows that it’s probably driving the LEDs with a positive voltage higher than BAT+.
The LED+ pad goes to the big diode, then from the diode to the inductor, and the other side of the inductor sits right on top of the vias coming through from the B+ spring on the other side. There's no way for LED+ to be higher than B+ in that layout.
LOL, that's way beyond anything I'm able to make sense of, especially in which parts of the example are relevant to the actual driver circuit and which parts are being done in some other way (like, how 'GND' in the diagram is something different than what I see on the driver - it's not battery ground).
My real guess as to some of this complexity is that they are doing something similar to what I suggested for converting the Knucklehead v3 to e-switch: latching turning all the components “on” while the button is depressed, and then holding (eg latching) them that way with the MCU and some small transistors until such time as the MCU sees fit to turn them off again (further button presses, LVP, etc). If that’s what’s happening it’s in order to eliminate as much parasitic drain as possible. That’s a lot of guesswork though.
What manufacturer is the sickle / swoosh mark on the part marked 82LE? I do not recognize the mark.
OK I'm lost. Using a 18650 at 3.98v and a single MTG2. In low mode, I get 3.98v at the input side of the inductor, 3.98v at the output side of the inductor, 3.98v at the diode's left pad, and... 5.24v at the diode right pad/LED+, which drops to B+ voltage when turned off.
LED+ to battery ground is 5.24v, LED- to battery ground is just a few mV.
MCU pin 1 to pin 8 is battery voltage. And, now, pin 8 has continuity to the ground plane. Makes no sense - how did reattaching the MCU create a ground, when none of the empty pads go to ground? Pin 8 is still ground even with the battery disconnected, so it's not being supplied by some other component. It's just there now.
(on 'turbo', it sends 6.48v to the MTG2, so in stock form it does a pretty serious output)
OK, pay no attention to the application circuit on page 1. That’s bootstrapping the LTC1871 to 5v, so that’s not what we want to pay attention to. Page 23 is starting to look like what we have here.
For your purposes, let’s get back to the point: We really need to know signal behavior during operation if you want to convert this to run on an ATtiny.
What is the behavior of X pin during on, off, and modes:
yellow
purple
pink
orange
blue
I suspect that most of them are simply on/off: they are either pulled high or low when the light is on.
Highly unlikely on the meter, it's a cheapie: http://www.prokits.com.tw/en/product/product_detail.asp?catid=1&itemid=MT-1232
I have a Fluke, but it's a low-end model and many many years old.
I'll get back to this later tonight or tomorrow, got a migraine that feels like a small furry sharp-clawed and very unhappy animal is trapped between my brain & skull...
OK... with power connected but the light off, I have battery voltage at pins 1, 2, & 4, nothing on the other pins (pin 8 is ground). Switched on, in low mode, puts battery voltage on pin 3. Medium = B+ at pin 7. High = B+ at pin 6. And turbo = B+ at pin 5. The 4 output pins are run only one at a time (when one is 'on', all the others are off). No measurable PWM signal anywhere. :(
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