Ohh, true, if you go with using both sides, not sure if it would work for this though, but maybe with the thin board. This was done with trimming diameter down, and direct soldering to the contact board. Space gets real tight. I suppose it could be done with a triple, having all 7135's on the backside. If so, then just need a pad for the pin freed up by the R1/R2.
Yeah, I could give something like that a shot. With that small FET it should not be hard to do. Might have to eliminate the zener and bleeder but it should fit. The resistors also may need to be 0402.
I will take a look at it when I have some free time.
Thanks for the vote of confidence 
I still plan on knocking out that 15mm driver before long, AC is out and 90+ degree temps in the house means that I have very limited motivation at the moment lol
Till then been trying to perfect bistro for the triple channel drivers to optimize the usage of the 7135’s and make it as universal as possible. I created a new thread on the subject of filling in the remaining 4 mode groups I have available here: Bistro for Texas Avenger drivers officially released! Still taking suggestions for future mode groups
Speaking of new threads, you probably saw, it, but your mention of the Ti buck driver above inspired to me figure out how to use it better (possibly/I think) than the MTN-MAX driver:
https://budgetlightforum.com/t/-/41762
So if you do ever want to get around to thinking about that, there were some nice ideas raised in the comments too.
Actually I had not seen that. I don’t have time at the moment to read it fully but have a look at this thread where I was floating the idea of a buck driver for the Q8.
Basically while possible and actually not that hard from a component / schematic layout point of view. For less then 3-5 amps it is also pretty easy to make it work.
It is quite hard on the other hand in the real world to deal with all the EMF that are emitted at high currents. 10+ Amps is something that many have tried at this point but no one has been able to make work yet.
Possible for sure but it would cost a fair amount in components and prototype PCB’s in order to get it working. If I ever have enough spare funds to take that on I plan to give it another go. Just not right now.
I already have the schematic and buck converter figured out (the datasheet has a good schematic to start from), just the components and layout that need to be figured out.
It’s funny you mention that. I’ve been wanting to do a RGBA (A=Amber) driver for a light saber, and I know how to get the firmware to work but haven’t attempted to actually make the circuit for it. I’m hoping to put 3x7135 on each of the 4 channels, and I think I have up to 25mm to work with (will have to double-check the inner diameter).
The idea is to make a rainbow saber, driving a quad XQ-E RGBA at about 1 amp per die. I’ll probably want to put a tiny85 on it so there will be plenty of room for fancy color patterns.
It may be a bit different than flashlight drivers, since the battery isn’t pressed directly against the driver and the host isn’t used to conduct power. I’m thinking battery carrier to charge port to forward clicky switch to driver to emitter pill. Would likely put the MCU in an odd place for easier access to it, like on the back of the driver where it has fewer wires connected.
I finally got a hot-air reflow station, but I haven’t actually made anything with it yet… and I still don’t know much about circuit design. So this is probably going to be a slow project, but I think it’ll be fun.
I could try to put together a circut for you TK if you let me know exactly what you need. Ideally I would like to be able to make it dual use for both flashlights and your saber but once I have the schematic drawn up it should not be too hard to adjust it to fit either.
I would just need to know the specs on the size and connection points/outputs. A picture of where it is going would be good as well.
I assume I could use the standard driver circuit we use around here - the FET parts.
It would be after the 15mm driver though, which I hope to get to next week.
I’m not exactly in a hurry. For now, I’m using my Astrolux S41 in the empty hilt. It’s just the right size, shape, and weight to counter-balance the blade for easier spinning, and as a bonus I can turn it on to make the blade light up. The way it barely fits into the back half of the handle, with the back end press-fit into the pommel, it’s almost like it was made for this purpose.
For the RGBA build though, space is going to be tight. In the back half, there’s just barely enough room for an 18650 cell in a compact battery holder. Then there’s a switch section with a narrower inner diameter, and all the wires will get crammed in there. The front section is 25.5mm internally and long, but needs to hold the driver, emitter pill, and as much blade as possible.
Alternately, the driver could be long and thin (~20mm x ~60mm) and be placed on the back side of the battery holder. This makes driver placement and layout easier but makes the wiring harder. Five long wires from driver to emitter in that case, instead of strapping it directly onto the back of the pill.
… and because the entire hilt is one solid piece (except pommel), I need to make the wires long enough to do the soldering outside then cram the wires in. Long enough that I can pull it out for later reflashing without un-soldering anything. It’ll be fun getting everything to fit.
Note the two screws near the front, one to hold the emitter pill in place and one to hold the blade.
This barely fits into the back half. I could increase available space a little by soldering wires directly onto a battery and omitting the holder.
Would like to make it use a forward clicky, but if I can’t find a suitable one I may have to go with an e-switch. The downside is more complicated code and relying on the charge port’s weak contact spring while power is on. It would send all current through a weak connection and I’ve had issues with that on other sabers. Like, random blade dimming or shutting off when it gets hit. Was planning to bypass that if I can.
FWIW, here is the emitter setup… (this one is 3x royal blue 1x red, but I’ll be doing RGBA) I think I can probably put the driver directly onto the back of the pill, with only + and - wires going to the driver.
That emitter pill, the wires normally go out the bottom I assume, is there a reason those wires could not go directly to the driver (I think thats what you were saying?)
The pill appears to be about 20mm internally, I should be able to make up a 4 channel board in that space, the issue is how many 7135’s you would need, to fit 12 of them would be quite interesting.
That said I think it would be doable, just. All you would need is 4x banks of 3x 7135’s with the SOIC8 150mil pads + C1 + R5. The FET parts are not needed , if there is room I can try to fit C2 and the LVP could use the internal reference correct?
Plus pads for all the channels + power + e-switch + ground.
I should be able to fit 7x 7135’s on one side, possibly 8 if you can remove that lip at the bottom of the driver / sand it down for more clearance so I can put the 7135’s right on the edge of the driver.
The pill has no “internally” measurement. It’s solid except for the wire holes, and it doesn’t screw into its shell all the way. So, the driver can also be up to 25.4mm in diameter; no need to fit it inside a pill. The wires would ideally go directly from the driver to the emitters, with the solid heat sink between. Which means the driver will likely be held in place by its five short forward wires. To expose the MCU, it’ll need to be on the back side somewhere.
I’m assuming there will be no room for an e-switch unless we drop the voltage divider and voltage sense pin, and instead use the internal ref/VCC method which has been tossed around but never tried. No OTC either, for the same reason, unless it uses Mike C’s combined-pin method.
Pins:
I’m hoping it won’t need an e-switch, but if so, that’s another pad or two on the back side of the driver. It’s weird having the switch between the battery and driver.
The driver will probably be pressed against the thinner switch section, which might make some of the layout awkward. Here’s the general idea:
The rear “button” there would actually be a charge port with its third pin unused, and the front button would need to be a clicky/latching switch. But an e-switch could go there instead, if I use all three charge port pins and connect a couple more wires to the driver.
Sorry this is getting so off-topic. This really has nothing to do with the TA driver any more.
lol, no problem on going off topic. I kinda started it.
It is late tonight but I think that can be done. I will create a new thread for it tomorrow and we can discuss the details there.
I think I would personally prefer to put it inside the pill if possible from a simple safety aspect seeing as it is going to get knocked around, it just seems more protected in there.
Also TomE or DEL has some working code for the internal voltage reference IIRC. It was posted in one of the firmware threads.
I haven’t seen the ‘New Thread’ come up yet, so I’ll post this here for now. 
Texas_Ace, ToyKeeper has already said that there is no ‘inside’ of the pill. It is a solid chunk of metal with only some holes through for wires. Do you mean inside of the shell that the pill screws into? I’m not sure, but it looks like the pill would screw into the shell emitter-first, with the TIR on top, so the shell holds the TIR against the MCPCB. The back of the pill would then be in open-air toward the hilt.
ToyKeeper, are you wanting the RGBA dies to be individually addressed? I know you’re the firmware writer, not me, but I’d think an e-switch UI would be monstrously easier to use. That is, unless you are just going to have some very limited functionality in your UI. I guess for a lightsaber that would be fine. Also, there’s no need for OTC if e-switch is used.
If the driver is to sit against the back of the pill, then the driver should also be one-sided, right? Both the Vin+ and Vin- would come in as wires to the ‘top’ of the driver. Then, there would need to be vias near the edge, in the right size and position to solder wires straight through the wire holes in the pill to go to the emitters. The rest of the ‘back’ of the driver can be a host ground plane, or nothing at all, since the host is electrically neutral.
You are correct, I was looking at the “pill” backwards.
Started new thread for light saber driver here: 4 channel Light saber driver design, may the light be with you.
Ok, I had some free time to give this a go. Here is what I came up with:
15mm, can be sanded down to almost ~13mm if needed
Kept components on 0603 pads, could give a bit more space if I went to 0402.
SOIC8 150 pads, so you will need to bend pins for tiny85
Kept FET resistors
0603 Pads for OTC / E-switch
0603 pads for pin 7, for later expansion / dual switch / indicator LED ect.
Kept it a triple channel driver with 4x 7135’s on the bottom
~5mm spring pad that should be just enough for a 105C spring
Large passthrough for 20AWG+ wire
Full copper ground pour to reduce noise and increase heat sinking. (also possibly why these drivers were able to manage a 1 PWM on the 7135’s)
All of the 7135’s will most likely need to have their center pins trimmed in order to fit.
I am indeed trying to make it dual use as both a normal clicky driver and e-switch driver (although someone will need to add the internal reference LVP to bistro as a selectable option).
Let me know what you think, if you see any changes you would like, let me know.
If you think it is good I will upload it to OSHpark and put it in the OP.
Didn't see this til now. Ohhh, this is nice! Wow!! Is this done or do you have more tweaks? Might have been nice to have a pin#7 pad on the component side, but not a must have. I'd order these asap. I can't see any probs. There's times when I'll have room to populate the 4 7135's, and sometime not. The 85 clearance may also be an issue in some mods because of the added height when mounted w/bent pins, but I'll have to see. At least I'd have an option to drop features from Narsil and try to squeeze it in a 2K for a 25. Thanx!! 
I can fit the 85 pads and put the pin 7 pads on the top but it will push the top side components out to the edges of the board and/or would need 0402 components.
You had said you wanted as much edge clearance as possible so I put that above those features as a priority.
If you would prefer less edge clearance let me know and I can update the design.
Oh boy, tuff call. Can't have a light that throws 1 mile at 1 oz and runs on a AAA?
Hhmm, I'd say leave it as-is. Would not be happy working with 0402's, and having space on the edges is valuable as well.
Well, it appears to me, in your photo above, that you only need the generous board edge at the top and bottom, not all the way around. If that’s true, maybe a bit of re-arranging can still be done to get the other features you requested. How much extra width really needs to be added to the SOIC 8 pads to make a Tiny85 just fit?
Edit: Do you really need OTC pads? Are you ever going to use this board with a clicky instead of an e-switch? Anyway, the OTC/switch pads may be able to move up and to the right a bit to make clearance on that side of the MCU. And the diode might possibly be moved up and to the left for clearance on the other side. It’s hard to be certain when looking at such a relatively huge picture of such a minuscule part. That over-poured pad for the FET can be reduced to make room for the OTC/switch pads. In fact, there’s more room on the right side than the left, so maybe even slide the MCU over a tiny bit to the right to make it easier to get clearance on the left.
I can rearrange things a bit, and already tried. I actually need to move the OTC pads (they are the e-switch pads as well, so needed no matter what) out a bit more anyways as they are a bit close for comfort when trying to fit a programmer on the MCU (should be ok with a tiny25 but not sure on the 85).
The components at this point are all approx the same distance from the edge, I could push them towards the sides a bit, it should allow for the pin 7 pads up top for sure but the tiny85 pads would be quite difficult, it would take up the entire bottom of the board, no components would be able to fit next to it and still put a programmer on it.
I will see what I can do to get the pads up top.