Dual In-line Adaptor Board?

XCore Project reviews, ideas, videos and proposals.
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The_RB
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Post by The_RB »

That's very nice work Omer. :)

You seem to have nailed that "strip it down to the minimum" concept quite nicely.

The size looks good, but maybe it could be shrunk a bit more? Getting the size down will help in costs as it saves costs on the PCB and the SMD placement because you can get more PCB on each placement panel.

I'm won't pretend to know anything about XMOS JTAG but how many pins does the programming interface actually NEED? It would be great to get rid of that big ugly connector... Even if it must have 20 pins I think a vertical 2x10 plain pin header would save quite a bit of wasted PCB that the angled IDC connector takes up.

And what will the dissipation of U4 be like (1v regulator)? If you have 3.3v reg and 1v reg on board, there is a chance that the user will just connect 6v or 9v to it, and I think that is going to cause problems for a number of reasons.

What I originally imagined was putting the 1v reg on board and run from 3.3v. So the 1v reg has a fixed and predetermined dissipation. Then the 3.3v reg off board, so the module is powered from external 3.3v. This reduces size, cost etc and allows for a larger 3.3v reg. It is not unreasonable in terms of functionality in that the module is basically functioning as a 3.3v powered "chip". It is likely that other external devices will require the 3.3v too.

Moving the 3.3v reg off board and changing to vertical plain 2x10 header and some tweaking could get that PCB down to 70% of its present size.


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bdring
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Post by bdring »

I would be interested in purchasing a DIP XMOS when available. Seeed Studio might be able to help get them made. They have business model that helps open source communities get things built.

http://www.seeedstudio.com/blog/?p=877

Check out the open source "bus pirate" for example. It is a pretty good price for what you get. I hope this long URL works

http://www.seeedstudio.com/depot/preord ... 92e812a31b
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Omer
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Post by Omer »

Hello folks,

Let me start off by saying Happy New Year to all :) Apologies for the late reply, I have been busy with travelling/general festivities!

As for your comments:
TonyD wrote: Should U4 LP3879 pin 8 SHDN be tied to the INPUT pin 4 and instead of the OUTPUT pin 5 ?
You are absolutely correct, I missed that completely! Thanks ;)
TonyD wrote: also have you considered taking the RESET signal to one of the 40-pins?
To be honest I haven't, as the number of pins I had was a perfect fit for the I/O that the chip provides :) I suppose I could add the reset pin, what would be the main advantage of doing this though? The simple RC reset circuit should be sufficient for the operation of the chip...
The_RB wrote:The size looks good, but maybe it could be shrunk a bit more? Getting the size down will help in costs as it saves costs on the PCB and the SMD placement because you can get more PCB on each placement panel.
Correct, but shrinking the board means spacing and via sizes will have to be smaller too which seems to be a more important factor when it comes to price. With the current size/specs, I could get PCBs for around $2 a piece at quantities around 50 and as this is a 'hobby' project rather than a commercial one that is good enough for me :)
The_RB wrote:I'm won't pretend to know anything about XMOS JTAG but how many pins does the programming interface actually NEED? It would be great to get rid of that big ugly connector... Even if it must have 20 pins I think a vertical 2x10 plain pin header would save quite a bit of wasted PCB that the angled IDC connector takes up.
I am using the 20pin JTAG configuration as I want to be able to program this directly using an XTAG1 or XTAG2 programming adapter. As for the IDC header, removing it will save space (and reduce cost) but I like 'fool proof' interconnects which reduce the frequency of headaches so I think I will stick with it :)
The_RB wrote:And what will the dissipation of U4 be like (1v regulator)? If you have 3.3v reg and 1v reg on board, there is a chance that the user will just connect 6v or 9v to it, and I think that is going to cause problems for a number of reasons.
Yes, the heat dissipation of U4 is a concern. I intend to play around with this when I get back to the lab, having board-wide copper pours should help this a little bit...
The_RB wrote:What I originally imagined was putting the 1v reg on board and run from 3.3v. So the 1v reg has a fixed and predetermined dissipation. Then the 3.3v reg off board, so the module is powered from external 3.3v. This reduces size, cost etc and allows for a larger 3.3v reg. It is not unreasonable in terms of functionality in that the module is basically functioning as a 3.3v powered "chip". It is likely that other external devices will require the 3.3v too.
Hmm, this is a tough one. I have considered the same scenario you have outlined but decided against it because I wanted this to breakout to be 'self-contained'. Having said that you raise an important issue with the heat dissipation and also the space savings so I guess I could be convinced that removing the 3V3 regulator would be a good idea. Further comments on this?


Thanks for your comments/suggestions, please keep them coming :)


Cheers,
Omer.
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TonyD
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Post by TonyD »

Omer wrote:......
TonyD wrote: also have you considered taking the RESET signal to one of the 40-pins?
To be honest I haven't, as the number of pins I had was a perfect fit for the I/O that the chip provides :) I suppose I could add the reset pin, what would be the main advantage of doing this though? The simple RC reset circuit should be sufficient for the operation of the chip...
No advantage really, I just find having an accessible RESET signal useful :geek:

Anyway, how's the board coming?
Are you planning on having some assembled?
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