Help with Current Sense Resistor Modding

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garrybunk
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I broke a corner of it off and one of the legs. Is there anyway to keep using the 105c with it (and get more output)?  I know I could always just use it as a contact board and run the light entirely off the 105c, but I'd have to wire another one up that still has the MCU attached. 

And so those ARE current sense resistors and NOT current limiting resistors? So going back to an FET would give me regulated output or not?

-Garry

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Rufusbduck
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On a 7135 driver loss of modes sometimes means the pwm pin is pulled high (usually because the led + pad is shorted to the pwm pin closest to D1) but a momentary switch should not be able to interrupt that. Is there anything else on the trace we think is the pwm that might affect the signal ? If there’s unwanted capacitance there might it not prevent the 7135’s from turning off the way they should?

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

wight
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I’ll tell you what I think:

  • Either the maximum duty cycle the MCU (or whatever it is) will provide is OR the 7135s just do not like something about the PWM signal (very high freq for example).
  • Those are current sense resistors but they are not used in a traditional way. This driver provides PWM output using an FET (like an East-092 driver) and varies the PWM to achieve a specified average current. That is not the same kind of output that a buck or linear driver generates. I’ve actually considered trying to do this but I decided that there must be some reason not to since nobody else was doing it. Kind of like the opposite of “if everyone else was jumping off of a bridge…” The average current is being regulated, this is not the same as what we normally refer to as regulated output.
  • You can probably grind the FET until that leg/pin can be soldered to. Using flux will probably help. Maybe carving with an X-ACTO knife could give better results than grinding/filing, depending on the situation.

I don’t think you have the ability to flash MCUs, but if you did you could use ToyKeeper’s STAR mod which features support for status LEDs. You’d just wire up the 105c to the status LEDs & their limiting resistors on the stock PCB.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
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garrybunk
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I already threw the FET away and can't find it. Is there any easy cheap replacement (like an EBay listing?). Any FET work?

-Garry

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Rufusbduck
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Would the AOD510 from one of the DD boards work? It doesn’t look like you’ve done anything beyond wasting that one part.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

wight
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Any decent DPAK FET which we’d use on a regular DD driver should work, AOD510 included.

RMM sells singles of IRFR3711ZTRPBF, that should be fine and I think it’s the cheapest option if you just want to purchase a single unit. Should be <$4 shipped.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
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garrybunk
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I've ordered 2 FETs from Mountain (along with other parts to keep on hand).  In the meantime, here are those higher res. photos I promised:

My final driver wiring after changing over to 22ga wires and removing the + wire (the PWM wire is the red):

1

 

Ground Wire on the Back Side Due to Thicker Area to Attach (and my stacked 7135):

1

 

Closeups of my stacked 7135;

11

 

11

 

Few views of being wired up to the main driver board with FET removed:

1

1

1

Really tough to show the wiring with so much in the way!  And those photos were prior to me moving the ground wire to the other side of the sense resistors.  This was the wiring that gave me no modes.

I'll post back when I get the FET and get it remounted. 

-Garry

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ImA4Wheelr
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^ Sweet driver mod you got going there.  That 7135 stack is just showing off.  So many of us wish we could stack those that well.

garrybunk
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Well it was sweet until it didn't work (you read that part, right?)!  It was good practice though.  And as I stated earlier, that was my first attempt at stacking 7135's and I found that to be a lot easier than attaching those darn 22ga wires!  I never had that slave board fully functional to see if I ended up with the proper current level (i.e. that I didn't burn up any 7135s). 

I tell you what though, I am enjoying the quality of photos I am getting out of a camera that I only paid $39 for! 

-Garry

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ImA4Wheelr
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LOL.  OK, semi-sweet driver mod.  Or, sweet looking driver mod.  What it lacks in functionality, it makes up in personality.

Or, I4W likes pictures and skim reads a lot.

Sorry about it not working yet.  Looking at the wiring, it looks like you have it connected properly.

Rufusbduck
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Poor Garry was led astray by a mad duck. The wiring looks exactly the way it should but unfortunately I was mistaken about how simple the swap would be. My bad. Once again, knowing a little will get you into more trouble than knowing nothing.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

wight
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The perpetrator did not act alone. Sad

We’ll get garrybunk straight in the end.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

LowLumen
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…rewind to post #1 and do the sense resistor mod.

Lesson learned: KISS

Rufusbduck
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True but you still learn more from mistakes than you do from things you already know. In a situation where failure is not an option kiss is more appropriate but not for something like this where you can go back to square one with little risk.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

ImA4Wheelr
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wight wrote:

. . . I don’t think you have the ability to flash MCUs, but if you did you could use ToyKeeper’s STAR mod which features support for status LEDs. You’d just wire up the 105c to the status LEDs & their limiting resistors on the stock PCB.

Do you know which modified version of STAR has this support?  I searched for discussion on the topic, but didn't find any.

wight
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ImA4Wheelr wrote:

wight wrote:

. . . I don’t think you have the ability to flash MCUs, but if you did you could use ToyKeeper’s STAR mod which features support for status LEDs. You’d just wire up the 105c to the status LEDs & their limiting resistors on the stock PCB.

Do you know which modified version of STAR has this support?  I searched for discussion on the topic, but didn’t find any.

Yes. Wink It’s the version discussed in comfychair’s Roche F6 Hacking thread.

She may have implemented the status LEDs in one or more of her other firmwares, but I know that they are present in this one for Helios-‘s Ferrero Rocher DD driver for the F6: http://bazaar.launchpad.net/~toykeeper/flashlight-firmware/trunk/files/h...

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
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ImA4Wheelr
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^ Didn't search that thread.  Searched the OSH Park and STAR threads.  Thank you. Smile

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Got the new FET from RMM mounted. Now I'm gonna power up and check currents from battery pack and at LED wires. 

A

Cruddy cell phone pic. 

-Garry

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garrybunk
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Ok here are my measurements at 4.2v battery pack (2 cells parallel @ 4.01v)

off: 0.011A

low: 0.98A

Med:1.30A

High: 1.75A

Now meter in line with LED wires:

off: 0.000A

low: 0.81A

med: 1.33A

high: 1.81A 

So I guess my LED measurements are higher because my battery pack wiring & connectors (maybe just my connectors I add to get inline measurements) are adding some resistance. Anyway, I'm pretty much back to stock output. What resistors would I stack / replace? Think my goal was about 3A on high (1.5A per emitter). I know I have R120's and think I have R500's. I have others but I'd have to look. 

By the way, I'm correct that the 1.75A I measure gets cut in half for "per emitter" current, right?

Thanks,

-Garry

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wight
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garrybunk wrote:

Ok here are my measurements at 4.2v battery pack (2 cells parallel @ 4.01v)

off: 0.011A

low: 0.98A

Med:1.30A

High: 1.75A

Now meter in line with LED wires:

off: 0.000A

low: 0.81A

med: 1.33A

high: 1.81A 

So I guess my LED measurements are higher because my battery pack wiring & connectors (maybe just my connectors I add to get inline measurements) are adding some resistance. Anyway, I’m pretty much back to stock output. What resistors would I stack / replace? Think my goal was about 3A on high (1.5A per emitter). I know I have R120’s and think I have R500’s. I have others but I’d have to look. 

By the way, I’m correct that the 1.75A I measure gets cut in half for “per emitter” current, right?

Thanks,

-Garry

Iout = Vref / Rsense

Vref = Iout * Rsense

Rsense = Vref / Iout

Therefore for 3A output you want something like 0.033 ohms for Rsense. Three R100’s would be good. Four R120’s is 0.03 ohms for ~3.3A output.

By the way, I’m correct that the 1.75A I measure gets cut in half for “per emitter” current, right? – Yes.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
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garrybunk
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Thanks. I'll try the (4) R120's and then measure again. 

-Garry

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Ok, I pulled the R100 and stacked (3) R120's (left other R120 in place). My resistors are supposed to be 0805 size from FastTech and they are 1/2 the size of the ones on this driver. Does that seem right? Is it ok? 

Anyway, current on the LED wire is now:

Low-1.32A

Med-1.80A

High-1.96A

I'm wondering now if the LED leads are too thin. Holding the lead up to 24awg wire I'd say its close to the same size, maybe a size smaller (26Awg?).  

-Garry

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Or could I have burned up a resistor? Or do the new Low & Med currents show the resistors are all good?

-Garry

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wight
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It may be that the thing has a maximum duty cycle it will not exceed. The new Med/Low currents do seem to indicate that the resistor mod is having an effect. Just not the end result you want for some reason. Sad

0805 sized sense resistors should be OK with 4 in parallel. They are quite small compared to 1206 sized ones, I prefer to use 1206 when I can. Assuming the 0805’s are good for 1/8-watt or greater, there should be no problem with dumping around 0.3w across 4 of them in parallel.

EDIT: no harm in replacing the leads.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
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So would you suggest adding another R120 just to see if High increases? Or just replace the leads? Do both? 

I need to get some 1206 sized resistors! These are too darn small!

-Garry

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By the way, I'm done working on it tonight. 

-Garry

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wight
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I recommend replacing the leads first. If that helps, great. If not, I feel that you have run into a limitation of the software that came preloaded on that driver’s MCU.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
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wight
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Copy/paste from my post in another thread: FT carries 3 values of sense resistor for 1206. Use the dropdown menus. http://www.fasttech.com/products/0/10007371/1615805-1206-0-12r-smd-preci...

For anything else you’ll want Mouser/Digikey/etc

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
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Thanks!

-Garry

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