Another little driver that won't be much use to most of you guys

Flashlight Modding and DIY Parts
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!!! Update April 13, 2017 !!! I need help again. See post #71. I’m trying to re-design my driver board, because I realized it wasn’t going to work. I decided to upgrade to a FET at the same time. I need some help trying to arrange the components on the tiny (now ~11mm) board.

!!! Update January 20, 2017 !!! I added even more vias to the alternate board. The newest alternate board is shown in post #62.

!!! Update January 19, 2017 !!! I added some more vias to the alternate board as Rufusbduck suggested. The newest alternate board is shown in post #59. I guess I need to go back and add vias to the regular driver board as well.

!!! Update January 16, 2017 !!! The latest revision of this driver is in post #47. And, there’s another board in post #50 which is a bit different.

!!! Update January 06, 2017 !!! The newest board design is in post #42 now. All components are within 5.5mm of center so it can be sanded down to 11mm diameter. Just sanding down the OSH Park Edge­­™ will leave you with 12.5mm diameter.

!!! Update in post #29 !!! Sorry, the board in post 29 won’t work. See post 40 from DEL.

Hey guys. I just wanted to post this up in case someone might be interested in it. It’s not for the barn burners. But not everybody wants to light up the whole world at once from a single hand-held device. Sometimes, just a little light is all you might need. Also, since I’m still very new at driver building, let alone driver designing, I’d like somebody who does know a little about this stuff to give me some feedback if ya don’t mind.

So, here we go. The driver outline is 13.28mm, according to OSH Park. Just sand down the OSH Park Edge­­™ to make this a 12.5mm diameter linear LED driver with only a single AMC7135 chip to regulate current for very small flashlights. The MCU is Atmel attiny13a MMU. The resistors R1 and R2 have a 0603 footprint, but 0805 resistors will fit. I used 0805 footprint for both Capacitors C1 and OTC.

I was really hoping to get a simple (old style around here) linear driver down to 11mm if possible, but I haven’t figured out how to squeeze this stuff any tighter, even with using the smaller MMU footprint of the tiny13 MCU. If any of you Eagle Masters wouldn’t mind helping me figure out how to cram this stuff into a tighter space, I would appreciate it. I know putting some components on the other side would work. Two sided drivers as small as 10mm have already been done, but I’m trying to keep this single sided.

I made this driver for (hopefully) modding a little Lux-Pro zoomie I found at Lowe’s a few weeks back. It has a rear clicky switch, and uses four little button cells to directly power a cheap LED. It’ll take some work, but I’m planning to squeeze in some kind of driver (maybe this one) and a better LED, and replace the button cells with a single 10180 Li-Ion to make around 150 LED lumens. Alternatively, I thought about stringing multiple LEDs inside a tube epoxied into the bezel to make a sorta stick light that will be small enough to pocket. With the added efficiency from splitting the current, it might reach close to 200lm output.

Here’s what I’ve got so far:

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Wow! That is tiny. And looks good!

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Shorter traces save board space so you could eliminate the outside loop and shorten the other trace for the voltage ladder by moving R1/R2 and led + around next to D1. Rotate U1 ~90 clockwise to their previous location. That puts everything connecting to B+ in the same area with a minimum of vias. D1 and C1 could stand to move south and inboard a bit more since you have two traces of separation from the mmu and it can’t be programmed after install there’s no need for clip clearance. You still might need to go to 0603 for the caps as well but this should get you closer.

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If that’s still not enough R1/R/2 are the thinnest components if shifted to the bottom and beyond that D1 and both caps can be easily connected to the mcu with vias. Probably need only a small B+ post and pad(3-4mm) with whatever of those parts necessary arranged around it. It might not be necessary. Just start by moving things to minimize trace lengths and blank areas as that’s the acreage you dont have to spare. Continuous ground is only needed on the bottom, just use vias to reach it.

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Thanks RBD! I’ll try moving the resistors around to the other side. I know this driver doesn’t need space for a clip because of the MMU package. I thought about using 0603 Caps, but with my present design, there’s no significant gain in board space. Maybe when I move things around, making smaller pads for the caps will make sense. For the light I have, this driver is the right size already (after removing the OSH Park Edge­­™ ). But, I’d like to cram things in tighter for other lights that don’t have ~13mm of interior space for a driver. If I can make it reducible to ~11mm, that would be nice.

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Hi DavidEF,

good work, keep it up, and thanks for sharing. Don’t worry whether someone else is nedding it, yet.

Do you really want to use the 20pin MMU (20M1)?
When I tried the MMU, I used the 10pin version (10M1). You have more space on the board and can better use traces under the MMU.

And I really love this OSH Park Edge­­™ remark. You made my day. :laughing:

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@RBD: He does not need to worry about a clip, I know of no clip that can reprog the MMU, the “pins” can hardly be seen at the sides, let alone reached by anything but a fine needle.
And what’s wrong with his number of vias (“with a minimum of vias”), I see 5 GND vias and a BAT+ via, all of them either useful or necessary.

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Looks like a good start :+1:

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I don’t really have any attachment to the 20 pin MMU. It’s just that it’s the version available at Mountain. I don’t flash MCU’s so I have to get them where available. Now, if you wanted to sell me some pre-flashed 10-pin MMU’s, I’d change the board for that! :wink: I like to have three or four lighting levels starting from low (or moon), mode memory, and no step-down. :smiley:

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What size components are those, they look like 0805? I would drop down to 0603 for sure for that driver (except for C1 naturally). You can still use 0805 components on the pads but 0603 is really not hard to work with.

Also, can the tiny13 use the internal voltage reference like the tiny25 so that it could handle LVP without the low voltage divider? That could eliminate the R1/R2 and save a lot of space.

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Just a proof of concept, obviously vias and ground plane are missing:

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outline is 13.2
yellow circle is 12.5
even 11 looks doable with this design
R1, R2, OTC are 0603
C1 is 0805
MCU is the 10pin (10M1)

It’s not like I reenvented the wheel, you’ll find it quite similar to my HQ10D, which itself consists of parts and ideas others were sharing and I did pick up.

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I just looked at the ATtiny13 datasheet. It does have an internal voltage reference, which it says is useful for brownout detection. I don’t know anything about it, other than that. Is the internal voltage reference a yes/no deal? Does it just being there mean that you can use it for LVP, or are there other considerations? Sorry I don’t know anything. :person_facepalming:

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I see your point with the 20pin MMU. If I start making a fortune by selling pre-flashed MCUs, you be the first to know…
In the meantime
With the 20pin version GND sits differently (which is the least concern). It’s larger. And lot’s of Do-Not-Connects on both sides.
You use Eagle? You might want a custom part stripped of DNC pads so you can use wires under the MCU.

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Is there going to be a problem with the MCU because of the back/bottom GND plate not being soldered down?

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I have no idea what is needed either, only that it apparently works lol.

Since I do not see this driver being used in anything but a 1S setup using an internal voltage reference should work well.

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Only if the MCU produces more heat than the package can dispose of without the soldered back. I can’t find anything substantial in the datasheet. But I truly assume that, as our Attiny13A are in sleep mode almost all the time, that it will work fine without the added heatbridge.

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You’re probably right. Additionally, this driver only has a single 7135 regulator, and will be running off a very small Lithium cell. So heat from all sources will be quite low.

Edit: So, any chance you’d sell me some pre-flashed 10 pin MMU’s?

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Yeah, I think there is even more heat coming from the LED to the driver to the MCU than is generated in the MCU itself.

As I wrote, if I start making a fortune by selling pre-flashed MCUs, you be the first to know…
No, honestly, I do not sell, I only have a flimsy breakout board and I’m not capable of testing post-flash. Did I already mention I sit in europe?

But RMM might be able to do it, if he already sells the 20pin, why not the 10pin? Might just ask him.

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Oops! I missed that post of yours before. :person_facepalming:

I hadn’t thought about making a new library part. That would work well enough for what I need. If I do that, as well as removing the LVP parts and moving everything around a bit, I could possible get the driver under 11mm diameter. Then it should work for most 10mm cell size lights (10180, 10250, and 10440/AAA) as long as they have length enough in the driver cavity.

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Don’t give up on the 20pin MMU yet, being able to get these preflashed from RMM is still a major asset.

Here another proof of concept, which might be very much along the lines RBD suggested:

Make C1 an 0603, use 0.254 instead of 0.3048 wires, squeeze everything tight together and you might even hit the 11mm mark… But the 20pin is huge compared to the 10pin…

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Thanks HQ! :partying_face: