Oh no! :zipper_mouth_face: I’ll fix it. I think I was just copying the info on the Oshpark link. Thanks for picking that up. I had wondered about it at the time but don’t know enough about components for that level of editing.
K, thanks! Funny, I just did the same exact thing - laying the diode on it's side.
See my new BLF17DD ref thread: https://budgetlightforum.com/t/-/27210. You and several others I'm sure don't need it now, but I'm trying to keep an online ref, specially for those this is all new to. If you notice anything amiss or may be needed there, shoot me a pm. Trying to keep the thread uncluttered. But the idea is to use the OP as a one source reference for the BLF17DD versions.
Hhhmm. Low voltage monitoring? What do you mean exactly? Is the SOD-123 diode the one you provide in your zener kit? The SOD-323 is the standard one used in the FET driver, and Nanjg/Qlite I assume?
Zener mods typically disable low voltage monitoring since the 19.1k resistor is the wrong value for a higher voltage and the Zener latches the input voltage so that the mcu no longer “sees” the battery. Separating the voltage divider from the Zener allows the mcu to once again monitor the battery voltage as it drops and only requires a new correct value for R1 to read it correctly.
Ok, soooo, wut does this mean? I think I might understand you, but I'm very confused... I didn't realize voltage monitoring didn't work with applying a zener mod kit, or did it? To Nanjg/Qlites or FET based?
With the zener, the MCU's voltage stays the same whether the battery voltage is 8v or 6v or 5.5v. It wouldn't see the actual battery voltage until it dropped below the limit set by the zener... and by that point the voltage would be far too low to be safe for two cells in series. The MCU would still kick in the protection only at the original 2.8-3v, which would be 1.4-1.5v per cell.
It’s true of any Zener modded nanjg board. It’s been know about but nobody bothered with it. Now, with the advent of the FET mods opening up more board space combined with the enthusiasm for new boards it got done. RMM and others worked up getting the layout corrected and new value(s) for R1/R2. The Zener can still limit the input voltage to the mcu while a new trace layout bypasses the diode to the voltage divider allowing the mcu to once again detect the change in battery voltage as it drains.
So the big question, does it work with 3 cells?
Why not? The zener can handle it, I don’t think you even need to adjust the 200-Ohm resistor. You’ve got to select your voltage divider resistors correctly for LVP though. Calculator.
Scott - I'm really confused now... Are you saying a zener version of the board has a different R1 and R2 valued resistors? Is this defined anywhere? I was wondering what the new R1, R2, R3, R4, and R5 values are to use on the BLF17DD-Zener Rev 2. Is this defined anywhere? I was figuring I had to trace the routes to figure out part assignment. I thought resistor values could change, or the firmware could change to adjust thresholds.
Yes - Richard's Super Shocker is 3 cells, 3 LED's in series using a zener mod driver. Others built 3S/3S zener lights as well. It's my plan, eventually...
Sorry, to specify I was talking about specifically the voltage monitor with 3s, I actually just finished up a 3s cell / 3s emitter light myself so I know it works but being able to figure out LVP would really be a nice touch.
I’ve got you now guys. The short answer is yes, LVP can work with multi-cell zener setups. It doesn’t just happen though - we use a voltage divider and that must be setup correctly. You don’t need any math to get the job done, or understanding either actually. You just need to know what to punch into the calculator I mentioned earlier: http://www.raltron.com/cust/tools/voltage_divider.asp
You know the voltage you want to shutdown at the light (2.9v per cell, 3v per cell, whatever... those would be 8.7v and 9v respectively in 3s setups). The stock values used in the STAR firmware will shutdown the light at around 0.5v coming out of the divider, but I do not know the exact value. RBD put some effort into it but I don't recall if we came up with a precise value. 0.513-0.517v may be about right for shutdown (not rampdown). To calculate the resistors for the divider, put in 3 values and the calc will give you the fourth, for example:
Input Voltage - 8.7
R1 - ?
R2 - 4700
Output Voltage - 0.513
That yields an R1 value of 75007.6 Ohms.
If you want to use the calculator to simulate the original Nanjg 105c divider, you must remember one more thing. In that setup there is a protection diode which reduces battery voltage before it hits the divider. You must subtract that diode's Vf value from the input voltage before running the calculation (Vf is in the neighborhood of 0.25v to 0.4v, look at RBD's thread linked above for more info).
RBD or RMM may chime in with more specifics about the actual working resistor values or a more precise "output" voltage than what I wrote. I haven't done much work on this myself.
Wight and I were knocking our heads together over this. On a standard 105C board the reverse polarity diode is in the circuit with the voltage divider so some voltage is dropped across D1, then more across R1 and the remainder across R2. The mcu compares the voltage drop across R2 with an internal reference voltage and does what it’s programmed to do. The ratio of R1 and R2 determine the battery voltage at which the mcu is triggered. With one cell, 19.1k ohms and 4.7k ohms provide the correct trigger voltage. With two cells I came up with ~48k for R1 if I leave R2 at 4.7K. For three cells R1 will be an even larger value.
I checked using 8.7v input, 4700 for R2, and .5v for the trigger and got 77080 ohms.
As you can see from the slight difference between me and wight a higher value resistor will cause the mcu to trigger sooner than a lower value one. The next step is to go to online and see what values are available and pick one. If you are using unprotected cells in series I would recommend erring on the high side.
This is still relatively new ground and not much testing has been done or documented with different value resistors so proceed with caution.
Also, the internal reference voltage of the attiny13A is noted for being only accurate to within 10% and while this may not be a problem with one cell it could make a situation with unbalanced cells even worse. If you go with 3 cells then test the actual battery voltage which the mcu triggers as you might need to adjust R1 up or down in value to compensate. And please post your results. More data is needed.
The Zener mod is a very clever adaptation but it seems a bit of a shoehorn in design. I’ll use it since for now it’s unique for its size/power but I’ll be watching for alternatives.
Thanks! So for this board: mtnelectronics - FET MT-G2, Richard worked that all out for two cells because he says it has low voltage shutoff and rampdown? Does it matter what the LED's driven are (ie: 2 XM-L2's or 1 MT-G2)?
Does he use a different value R1 or did he change the firmware?
Not sure what RMM did but if he says it works then bank on it. 2 XML in series or 1 mtg shouldn’t matter to the board. By changing both R1 and R2 and adjusting the firmware it might be possible to improve the accuracy but that’s a tad beyond me just now.
Ohh - ok, hopefully he will enlighten us mere mortals 
. Absolutely I believe him, just thought maybe he published the "how" and I missed it. I think his testing is the most thorough around. I'm thinking he worked it out for 2 cells (MT-G2) and 3 cells (Super Shocker). I feel bad bugging him - busy guy to say the least...
Were all here to help. I’ve only really encountered the “shut up and do a search, boob” on that other forum. And since it’s about one of his products he shouldn’t mind. If he did alter the firmware then you probably should not use his values for R1/R2 as a guide for your own mods.
Gosh, and I thought we were still on drivers!
I’m sure there’s a joke in there somewhere about improving your drive 