[Oshpark] BLF SRK FET v3 (46mm / LFPAK56 / Dual+Triple Channel / ATtiny13A+85)

Well, when you've ben writing C code since '81, you learn a few things... But there's always new things to learn - that's a big reason why I like what I do so much.

Tom, can I freely choose between 85 and 85V for your firmware?
NarsilTriple.c and tk-attiny.h only mention “85”, but I recall the V-versions being more reliable because they work down to 1.8V.
85 is 20 MHz, 85V is 10 MHz, does firmware detect this by itself or do I have to make changes?
Much obliged.

Should be no problem with either MCU - nothing in the firmware special for either. I bought a few V's in the beginning and freely mix them up. Just fyi, I did some low voltage testing on a 85 (no V). We run them at 10 Mhz btw. I could run the light down to 2.3V without a hitch, accept the LED was a very light glow. I was pretty much amazed btw. The 350 mA 7135's, maybe combined with DEL's new 25/85 circuitry allows us to run with a PWM value of 1 with no prob, even on a drained cell. The 85 is spec's down to 2.7V, but add 0.2V for the diode, and you have 2.9V as spec'd low, but it ran on a cell at 2.3V, and since the LED is totally useless at that level, I don't see any problem at all. I literally had to cup my hands over the head to see the LED light up, and could only tell it was lit from turning ON/OFF - slight difference. I don't recall ever being able to do that, or anyone else posting bout it!!

Dunno, dunno why - maybe the 85 PWM rates, maybe DEL's great tweak on the circuit, maybe the 7135's, but the 7135's is the same batch I bought from FastTech years ago, maybe a combo of all these things.

I've been buying all my 85's from Richard - dirt cheap, cheapest around, and all he has is the 85's no V. Since basically no one has been buying them except for me, he's still got 55 in stock at that great price. I'm afraid if they ever do get popular, he'll have to buy a new batch and charge twice the price. His price is $1.35, while Mouser is over $2 in qty 10 or so, last I checked. Richard literally makes pennies on these things - amazing he even bothers, but he's there to help, not just sell/make money.

Ohhhh - btw, the spec sheet on the "V" says 1.8V-5.5V only for clock rates of 0-4 Mhz, which Narsil doesn't do, or bistro. For 10 Mhz, it's spec'd exactly the same as the non V MCU's: 2.7V-5.5V

Oh bout the clock rate, it is, and must be 10 Mhz -- the fuse values are for 10 Mhz, and the code/build is for 10 Mhz. If you want to tinker to lower the rate, by all means go ahead. I think DEL, maybe couple others used a lower rate fine, but PWM rates I believe will go down quite a bit. For me, I see no point in dropping from 10 Mhz, but the option is there. We had discussions bout MCU rates a while back in the 25/45/85 thread. Think Halo wanted us to go lower as well -- forgot, another reason as well, maybe...

Wow, very nice driver board. Way too many components for me to understand it. I’m sure there’s a kitchen sink around there somewhere. :wink:

About to pull the trigger on qty 3. $17 is a bit of an investment, but think it's worth it. I could use these as FET+1 or triple - looks easy to configure, and I still got a few SRK's to mod.

Edit: Ok, ordered!

If you get rid of the FW need for an external voltage divider for LVP, you can just leave R1 unpopulated and use the current R2 pads to run an indicator LED off pin7.

Sorry, it’s fairly obvious, but I just thought of it so clearly I had to say something :face_with_monocle:

Would additional components on the board be needed/useful for an indicator LED off pin-7?

I haven’t used one yet, so my guess is you would take the R2-pads for a bleeder resistor. Connect the indicator LED to the MCU side of the bleeder resistor or the free pad on R1. What about the resistor in series before the LED (R5 on the Q8 board), not needed?

@TomE
Thx for the clarification on the 85/85V. Will order, can’t resist anymore

Just a small update.

I changed R1/R2 (still the build of post #1) to 330k/82k and that brought the current in off-state down to 11µA (0.011mA) with a cell that is 3.3V resting. With 33k/8k2 it had been ~68µA after the ADC_off() firmware mod. So in the end I’m down from ~200µA to 11µA which is very very good.
LVP is still working as before and triggering effectively at ~2.9V. But I’ll keep monitoring that. TomE, great help, the firmware changes made for the major part.

While at it I installed a 33R as series-gate-resistor (Rgate). Not sure if it’s needed, as the FET is not PWM’d, but it can’t hurt to have it in place.

HQ - just found out the LDO requirement is Vout on pin #5, not pin #3. That's an important spec, so I just found out. TA's LDO drivers are wired the same way. Think you got it from Richard's BLF SRK V2. Weird because Richard's other LDO drivers have Vout on pin #3. The LDO's I bought from Mouser, and one I got from Richard have Vout on pin#3, so of course there was smoke when I tested it . Fortunately the only thing that seem to smoke was the 4.7 ohm resistor, so easy to replace, but I have to wait on an order of LDO's with Vout on pin #5.

Thx for the hint, I’ll added a note to the partlist.

Vout on pin5 was to my knowledge the sole version here on BLF for the SOT-23-5. Mattaus used the LT1761 in his Knucklehead V3, wight proposed 4 different LDOs with the same pinout for his AxxDD-SO8+LDO and yes, RMM used it in the BLF SRK V2, I simply kept it so.

Such a pretty board… sometimes I come here just to look at it :wink:

It's also purty in the flesh, ahh, I mean FR-4 and copper, or whatever these things are made from . Wai'tn now for the LDO's.

Forgot bout that thread. The wrong LDO I bought Richard used in the TK61 driver he designed, listed in the OP here: https://budgetlightforum.com/t/-/31955

Figured it was well tested as he stated, so had to be a good one - PN# MC78LC50NTRG, spec here: http://www.mouser.com/ds/2/308/MC78LC00-D-110708.pdf

Again - this is the wrong one. Who knew?

Wait til you get a glimpse of her next sister :wink:

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@TomE, yes, that’s definitely a different LDO pinout on RMMs board. One can only guess why he changed to it, but at least layout did not dictate it.

Ohh - been working on this:

It's gonna drive this:

Firmware has been tested. It's Narsil as the baseline. The table of voltage levels have been updated to support the 360K/47K R1/R2. It comes straight out of the spreadsheet I used to calculate them. It's conditionally compiled in, as below. The calculated values work very well now. Found a bug in indexing these ADC values where indexing was off by one. Not sure, but thought I got this code from somewhere else, maybe Bistro?

#ifdef USING_360K
// The ADC values we expect for specific voltages: 4.4V to 8.8V (2.2v to 4.4v). This is
//  for using R1=360K/36K, R2=47K/4.7K, and direct connection from Batt+
//  to R1, no diode in-between, with an LDO and a 2S battery configuration.
#define ADC_44     236
#define ADC_43     230
#define ADC_42     225  // 100%
#define ADC_41     220
#define ADC_40     214  //  75%
#define ADC_39     209
#define ADC_38     203  //  50%
#define ADC_37     198
#define ADC_36     193
#define ADC_35     187  //  25%
#define ADC_34     182
#define ADC_33     177
#define ADC_32     171
#define ADC_31     166
#define ADC_30     161  //   0%
#define ADC_29     155
#define ADC_28     150
#define ADC_27     145
#define ADC_26     139
#define ADC_25     134
#define ADC_24     129
#define ADC_23     123
#define ADC_22     118
#endif

That driver used to be a lot roomier. :confounded:

:person_facepalming:

@TomE
now we know where the driver got to…
just borrowing your picture :innocent:

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I hope you can fix the 7135 issue. Even if DEL more or less had ruled out a thermal issue I will make the connection of Q1 to GND wider.

Any other ideas or needs for changes in your book?

That mod sounds good. Dunno bout anything else - I like all the versatility this driver offers. There's plenty of thru holes for Batt+, but I'd still like to do something more there, but not sure how. I'd like to be able to solder fill the thru holes but not sure if the holes are wide enough. Hard to see but the holes themselves appear to be covered in purple soldermask but I'd like to see the entire holes to be bare ENIG. This way solder filling should work well.

This is what I did for the contact surface:

Got from here: etsy.com brass-discs-20-gauge (might be cheaper direct from their shop: https://boppermetalsupply.com/) in 1 3/8" size that fit well. All I did was drill the center hole and sand it down to get it flat, then reflowed to the driver. Bad thing was I added the brass disc only after reflowing the parts, so didn't get the PCB heated enough to use hot air, so had to use a torch.

Brass is preferred (to me at least) because it's harder than copper and I don't think has as much problems for electrically conduction loss from oxidation.

The thru holes seem to have filled up with rosin and not solder paste unfortunately. If I were to do this again, I'd apply solder paste maybe on the component side and apply the heat on the battery side to see if I could fill the holes first, before reflowing the copper disc.

From the picture above, clearly the larger ground thru holes are not coated with soldermask. I didn't closely look at the Batt+ thru holes though - I might be wrong there.

What is the rationale for calculating R1 and R2 in cases like a 12V SMPS input source, instead of battery cell(s)?