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

Another thought, with left side mmu pads eliminated, swap the 7135 with everything but OTC and route pwm under mmu. Maybe rotate the mmu so the gnd side flat is aligned to the board edge instead of it’s corner and put a gnd via under the mmu.

The inner yellow circle has a 5.5mm radius (->11mm).
Getting closer.

Gaining space below the MCU doesn’t help, no component fits. So I swapped D1 to the right again.
Still the notorius OSH Park Edge­­™ has to be considered. :frowning:
But it looks promising.

@DavidEF, if you want the .brd with the custom parts, PM me an email (preferably an anonymous one).

Now my TimeZoneGap will commence.
Goodnight.

L+/L- could be much smaller(1mm) if they were vias solder able from the bottom. 10xxx cells are all small contact on the positive end so a .4mm (?) via should work for L- if between B+ pad and outer ground ring. B+ input via becomes L+ eliminating that pad altogether.

Wow! You guys are great help! RBD, thanks for all the great space-crunching ideas. I meant to work on this board again this afternoon, but I forgot. I’ll have to try to remember tomorrow afternoon. HQ, thanks for all the work you’ve done on those board designs. Don’t worry about the OSH Park Edge­­™ being a problem. These boards can be sanded down pretty easily. I’ve been adding extra diameter to my boards just to accommodate it. If we can get the real diameter to be as small as possible, then the OSH Park Edge­­™ doesn’t really hurt anything except making the boards cost a bit more.

Update January 4, 2017: Ignore this post. See post 40 from DEL. This board isn’t going to work.

I made a new, even uglier version of the driver! I deleted R1 and R2. LVP will have to be implemented using the internal voltage reference. By doing that, and also using a chopped down MMU part, I was able to add another 7135 and still squeeze everything into 11mm! To clarify, the overall size of the board is still 13.28mm including the OSH Park Edge­­™, but all the components are fit within a 5.5mm radius from center, so it can be sanded down as far as 11mm diameter. Just sanding down the OSH Park Edge­­™ only still gives a 12.5mm diameter, which is what I’ll be using if I get to do my mod.

Did I say it was ugly? :confounded:

That weird shaped exposed copper at the top left is the LED and the other one at the right, hanging dangerously close to the ground pad of the 7135, is the LED+ solder pad. Sorry RBD, I didn’t use your idea to make those into vias. I also didn’t label very well. Only D1, C1 and OTC are even labeled at all. But at least I got my name on the back! LOL! I may go back later and clean up the look of this board a little and add labeling for components. Maybe. I’m tired now.- :weary:

What size is the C1 pads? The smallest 10uf I know of is 0805, which can be installed on an 0603 pad but nothing smaller.

It’s a 0603 pad, but it will indeed be a 0805 cap. I guess for consistency’s sake, I could either make the OTC pads also 0603 or change the C1 pads back to 0805. I just didn’t think about that last night. I guess I was more tired than I realized. :weary:

Ok, an 0603 pad will work, just have to be more careful with soldering it but not a big deal. It looked like it could be a 0402 pad which would not work.

I ain’t gonna be sodderin nuthin anyhow! :open_mouth:

I’ll reflow these if/when I build them. :crown:

Don’t want to baffle anyone but to measure voltage without external components the mcu doesn’t only need an internal voltage reference. It also must be able to measure the internal bandgap (voltage) reference against Vcc and I’m not sure whether Attiny13 is able to do this. Don’t have time to check the datasheet currently, perhaps someone more experienced could step in and clarify this.

I hope somebody does clarify for us. I can go back to having only one space for AMC7135, and put the R1/R2 back. I might just do that anyway, so all the “normal” ATtiny13a firmware will work with it, including biscotti.

Edit: I just looked through the datasheet a bit. The internal voltage reference is mentioned several times in connection with the ADC and BOD. But, I don’t understand a word of it. :person_facepalming:

On the other hand you could simply use a Attiny25, only minor changes to the code required.

Do you know of a trustworthy place I can get ATtiny25 MMU 20-pin chips for a reasonable price including USA shipping? Oh yeah, and pre-flashed with custom firmware!

Edit: Mouser has ’em for a reasonable price. Anybody want to volunteer to buy them for me, flash firmware to them, and mail them to me for cheap?

Just a tip… that 7135 ground tab is mighty close to the other 7135 outer pins. I’ve had shorts with them that close. What I did was create a custom 7135 with shortened ground tab, and then cut the tab down on the 7135. Buys some space.

And why avoid 0603 size components? I use them on all 20mm and lower drivers, even if space is not an issue. They’re easy to handle. The only components I need 0805 or larger are the big caps for OTC less design.

Thanks, Mike. I thought it looked close too, but I didn’t think it would short. If I re-work the board to put the R1/R2 back, then it won’t be an issue. But if I don’t do that, maybe I’ll change out the 7135’s to a cut-down pad just to make sure.

I’m not really avoiding 0603 as much as I’m just using what is easily available to buy at Mountain Electronics.

The 13 cannot measure the bandgap against VCC, so unfortunately the software-only method for LVP is a no-go.

(Compare the ADMUX register descriptions on the two datasheets. For the 13 you do have the choice to use either Vbg or Vcc as reference. But you cannot measure Vbg using Vcc as reference like on the 25+.)

OK. Well, I guess that means I’ll have to change it back to a single 7135 and add R1/R2 back. While I’m at it, I’ll clean it up a bit. Thanks for stepping in here and advising, DEL!

Here, let’s try this one. :innocent:

If you cut the 7135 tabs (custom footprint) and used 0603 components, you could fit it all with a little space to spare:

I’ve used a 85 with bent legs here, it’s a little bigger than your MCU footprint, but still have a little wiggle room. Visible border diameter is 12.5mm.

Also, there are 10uF 0603 caps. Here are the ones I use: http://uk.farnell.com/tdk/c1608x5r1a106k080ac/cap-mlcc-x5r-10uf-10v-0603/dp/2211164
They aren’t X7R rated, but do you really need X7R ratings for this driver?

Thanks, Mike! That looks really good! I do have 0603 components on my latest board revision. The light I’m planning to use this driver in has a 12.5mm shelf, so your design here will fit in the light. I left it at only one 7135 on my design so that all the components fit into 11mm diameter, because that could fit in a lot of AAA size lights, whereas 12.5mm seems to be less likely. But, when it comes to actually doing my mod, I might still go with the two chips instead of one. I guess I haven’t really decided yet. :stuck_out_tongue: