Hawkeye

Small Modular BLMs via OSC?

39 posts in this topic

KiCAD is an excellent tool - highly recommended, also for complex designs.

Back to the original topic: would you need 1 LPC core per BLM module, or is it so that one LPC core can handle the maximum size matrix you have in mind? This, IMHO, would be a clear indicator for whether to include the LPC socket per (modular) board, or keep it separate.

Edited by ilmenator

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Hi Ilmenator,

as far as I can see, it would be one LPC core per large BLM module of 17x17 buttons/duo color LEDs.

If there is a solution to drive more than one large BLM with a LPC core, I would be fully convinced to go "modular", because the design goal for this project is minimum build cost.

But I doubt, that it is easily possible, because one large BLM already uses 5x3 (=15) 74HC595 shift registers (5 MBHP_BLM_SCALAR modules) and as far as I know, the limit is 16 (or 4xDOUTx4).

Of course, one could try to increase the matrix by not using two shift registers for 8x8, but by using four shift registers for 16x16... I don´t know if it would be possible, also regarding LED current requirements (for an 8-LED-matrix, there are BC337 transistors employed, I have no idea, if they would be sufficient for a 16-LED-matrix).

Currently, I also have some concerns of how to fit all the necessary traces on a two-layer board with this really dense button/led packing :-).

Greets,

Peter

Edited by Hawkeye

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Currently, I also have some concerns of how to fit all the necessary traces on a two-layer board with this really dense button/led packing :-).

Could you provide a link to the footprints of both buttons and LEDs?

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Hi,

on the first page of this thread, you find an overview picture montage of the planned unit in correct relative sizes... it is 600x800 pixels big and every pixel corresponds to 0.3mm giving a total PCB area of 180x240mm. If you scale the picture in your browser to 18x24cm, every component should be correct size :-).

The switches have a pin-to-pin spacing of ca 7.5mm, the switch grid should be 10x10mm.

The LEDs are 3.2mm x 1.6mm.

Still missing in the illustration is one SMD diode per switch, which should be smaller than the LEDs.

I am planning for partial SMD coverage of the backside for the MBHP_BLM_SCALAR components and want to route the backside tracks to the frontside with vias to connect all switches and LEDs.

It is a next-to-impossible first project for learning PCB routing, typical :-)

Greets,

Peter

Edited by Hawkeye

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I just wanted to know where the soldering pads sit on these switches - I cannot see that from the bird's eye perspective fotos :unsure: .

Also, it might make sense to use through-hole diodes for easier two-layer routing... but then you won't have a clean PCB top side.

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Hi Ilmenator,

sorry for the missing information - the solder pads are 8mm apart on the left, respective right side of each switch. Vertically, they are centered:


  ----

_|    |_

 |    |

  ----

You can see them in the photo of the first posting of this thread (slightly blurred, but still visible).

I cannot provide you yet with a manufacturer link, because I´ve obtained them very cheap on ebay, but would be looking for another supplier before routing, so the PCB can be reused by other interested users.

As far as I´ve seen on the Alps webpage, these kinds of SMD switches are fairly common (5x5mm integrated button, ca 8x8mm case, soft feeling).

Nevermind the clean PCB top side :-)

I also have the strong feeling, that using a larger BLM matrix (e.g. 2 + 2 shift registers for a 16x16 matrix) increases the routing difficulties :-).

Greets,

Peter

Edited by Hawkeye

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This is the datasheet I've used for these switches http://www.alps.com/...t/SKPG/SKPG.PDF To the best of my knowledge this is the correct one.

Hawkeye, I think maybe you'd be better off thinking of this as a 3 or 4 layer design. Cost will increase but I think it's the only way to achieve the compactness you're looking for.

Still haven't finished soldering mine. Back at university now. Hopefully get done on wednesday.

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Please, no hurries, it is not so important.

I will look into multilayer designs, when everything gets a little bit clearer :-)

And thanks for the datasheet link, that is it! :-).

Greets,

Peter

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I hurry for myself too :)

Soldering complete. There are some minor issues that I should be able to sort out but I won't get to troubleshoot them until the weekend. For now, I offer merely a pic in the gallery. :flowers:

One lesson learned: double check schematics before getting boards printed!

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I've got a wiki page up now, with some of my BLM design files for your perusal. There's a list of current issues which is required reading before downloading.

I'm going to attempt a slight relayout of the BLM to allow for more sensible mounting hole locations, but I'm not sure I'll achieve it.

http://www.midibox.o...p?id=findbuddha

:)

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Also, it might make sense to use through-hole diodes for easier two-layer routing... but then you won't have a clean PCB top side.

Okay, the way you did the routing you could have also used SMD diodes... I was actually refering to the idea of using the diodes to get vertically across the horizontal 8-channel busses. But you've got a clean layout already!

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findbuddha, thanks very much for your schems - will look into them after work :-)

Are these the corrected ones (as far as I remember, there was a wiring problem somewhere)?

Great work on the "big" unit, btw! :-)

Greets,

Peter

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I'm trying to maintain a complete list of issues on the wiki page... My small BLM that is fully soldered is the 5x17. It's just the lowest 5 rows cropped from my (original) full 16x16+X. In general I'll be posting design files exactly as I've used them - the 5x17.brd contains the error documented here:

The blm-full.* design files are for the full 16x16+X. They have been corrected for the above error, but have not been tested. I should be able to order it in the next month or two.

Hope that makes sense :)

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Thanks a lot for the schematics - it all looks very clean to me... I will wait until your final order before adaptation (not because of missing interest or lack of faith, but because of only 24 available hours per day :-)).

Greets and keep up the good work!

Peter

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