Universal PI Micro

[Pete the Builder]

OK, here's the first attempt. I can't attach it as a bitmap or image, 'cause it's too dense. (A bit like me!). So it's in PDF form.

Please go over this, and just double-check that I haven't missed anything silly! Also, if you can, please verify that it matches the correct (i.e. latest) schematic revision.

I've made a few minor, and one major (but invisible) changes to the circuit. Here are the changes I've made :
- I've renumbered the parts. (I can undo that real easy if it's too much of a headache comparing. Most of the subcircuits are blindingly obvious, so it shouldn't be a brain-baker).
- I've added a standard cap and pullup to the reset input of the MPU to meet the Atmel specs. BW was extremely lucky that the floating reset input allowed the system to work at all! I'm assuming, therefore, that he had the programming header connected all the time.
- I've changed the 24x1 SIL headers to 50-pin (25x2) headers. You can use SIL, DIL, or boxed IDC headers as connectors with no changes.
- I've changed the main reg to a 7805 instead of an L05 (this has better line rejection and lower output impedance - both good things in this circuit)
- I've also added a VCC rail to the "spare" pin of the 50-pin header.

A bit of explanation is necessary about the last two changes : I really try to avoid multiple regulators on a single small system - they're just additional points of potential failure. There's no reason why the 7805 can't supply plenty of 5V to all the cards in the system. So by making the motherboard regulator a 7805, and adding the extra bus line, it allows two options for everyone : have all the boards powered exactly the same as the original design - in this case, you don't need to do anything. Just ignore the 25th pin, and the original boards will work perfectly. The second option (that I'll be using) is to use the supplied 5V rail to power the boards.

It's entirely up to you if you want to take advantage of the single power option, and you don't have to do anything either way. Just move a jumper on the daughtercards, and that's it.

I'll provide a design for the daughtercards that does the same thing - build it with the additional regulator on each board, or you can ignore the extra regulators and use the supplied 5V.

I hope this way to a) allow anyone who really, really, really wants to use the exact, same, identical-in-every-way design of BW to do so without even thinking, and b) let anyone who wants a more reliable supply and mounting system to be able to do so with almost no changes to anything - just a jumper on each daughtercard. I think that gives us the best of both worlds, but I live to be corrected. And of course, this needs to be tested thoroughly - this is something really basic that can catch up to you and ream you while you're not looking! So I'm not assuming anything with this change - not until it's been tested to death and verified that it's at least as reliable as the original. I hope that puts any nervousness at ease!

I hope this design looks right, and please let me know right away if you find anything wrong. As soon as I've heard back, I'll start the PCB design. In fact, I've started playing with the rat's nest already. It's going to be, er, fun to get it fitting the original PCB area...

Cheers everyone!
-PtB

Switched Cap Motherboard 3.pdf

[moscadondres]

Hi Pete ,
Very nice work,i hope more

[WM6]

Hi Pete ,
Very nice work,i hope more

Yes, good start PtB,it will be most on your own, but we all support you.

[Pete the Builder]

A PCB to have and to hold...

OK, here's my first-pass attempt at a PCB.

I'll just post two images first off, to get everyone's feedback on size and layout.

This first attempt is a double-sided board, and it probably needs to be manufactured, unless you have experience with making double-sided boards. I've got a quote, for just one board on it's own is about US$70. That's the minimum, and I'll be making at least one for myself. Subsequent boards are much cheaper - for example, if 6 people want one, the full cost per person is US$25.00 That's for a solder-masked, silk-screened, through-hole plated, double-sided FR4 1/2oz copper board - better quality than anyone can hand-make. But it IS doable, if you've got experience. I've tried to minimise double-sided traces where possible.

I'd guess that we won't want the main board made up until the daughtercards are done, which is my next project.

If people prefer a single-sided board, I'm working on that, but it will be a bit larger and it will take some time, as I'm hand-routing everything.

This board is 3.75 by 3.25 inches. The main changes I've made (as we discussed earlier) are : a full 5V positive regulator, which means no additional regulators on each daughtercard; boxed DIL headers for the daughtercards, which can be converted to SIL headers if you prefer, just plug in the header to the appropriate holes. And the reset circuit has been added. I've also added some bypass caps, and the final release will be ground-planed top and bottom.

All the rest of the circuit is exactly as Bugs designed it, even the pin numbers are the same!

Here's a really crappy 3D image of the board...Who knew that Altium's $6,500 software can't print the 3D view for nuts?


... and here's the board layout showing the top (red) and bottom (blue) traces. Part overlays are green. And for some additional reason that escapes me, Altium won't show vias in Assembly view. But the vias are in the final output, so please ignore the bug.
The final silkscreen will have component values for caps and resistors, and connector names for the connections, so it's really easy to build without needing the schematic. All part of the service!
Note that the overlay view is the latest revision, and is different to the 3D view. The 3D view was an earlier revision, but it shows the parts in their correct places, and the mounting holes and so on. Just the traces have changed (for the better, I hope!). Sorry if that's confusing.


Let me know if you're OK with this, and I'll go on to the daughtercards.

Cheers,
PtB

P.S. I just realised that I forgot to mention something important : if you already have daughtercards made up, they will work perfectly in this motherboard with no changes. Just a thought.

[mickstv]

Hi Pete, VR2 in the schematic is wrong, you have a 79L12 but the circuit looks like it needs to be a 79L05.

[sido]

Hi Pete, VR2 in the schematic is wrong, you have a 79L12 but the circuit looks like it needs to be a 79L05.

Hi Mick, have not compaired BW schematic, but good pickup on the "V" regulator specs.

Where is the single uC schematic design as the one PtB has posted? Is there a PIC sourse code provided already, or is it to be developed in due course?? according to the basic design parameters developed so far?....I am confused as to its forwarded format.

I must of missed something

Is it possible new threads can be created from the past to the NEW to aid the experimenter....instead of shifting through past documents to have a basic understanding of what is being forwarded now?

I may be missing some stuff with the whole project.........as i have may misunderstood the design changes to a single uC?

Sorry for my incompetance.

Am i the only one....maybe i am

Cheers Sid

[moscadondres]

Hi mickstv,can you tell the value of vr2,thank you.

[Tinkerer]

Hey guys, the one thing that is amiss here, is that nobody congratulated Pete for his great job and thanked.

Thank you Pete, for all your effort and sharing it with us.

All the best

Tinkerer

[joop]

Pete, thanks for reviving this project! I will keep an eye on it, might have a go at it eventually... Hope you will succeed in creating single boards for this project.

[Pete the Builder]

I forgot to add a huge "thank you" to mickstv for catching a massive error on my part, and preventing a lot more pollution from magic smoke! So
Thank You, mickstv!

I owe you at least one beer!

Ah well. Hell, if you're gonna make a mistake, make it a big one, right? And it wasn't even a footprint or component problem, just a part comment that would've sent builders astray... Sigh.

Oh, OK, I've just found out I can't edit old posts, so I've pulled that document, and I'll post an updated copy below. Gngngngngnnnnnn!

Anyway thanks to everyone for keeping an eye out on me!

-PtDB

*D as in "dodgy"!

[Pete the Builder]

Corrected UPIM Motherboard Schematic FEB2013

OK, here's the actual, corrected schematic.

Note that the internal font Altium uses does get better with expansion. 'Course, it doesn't help when your medication gives you binocular diplopia (each eye sees two slightly offset images...)

I'll hopefully be working on the daughterboards tomorrow (Tuesday). Fingers crossed!

Cheers,
PtB

UPIM Schematic 1.02 Feb 2013.pdf

P.S. I can't seem to delete the original using Chrome on Win7 x64, the forum software's uploader goes crazy. When I get on the laptop, I'll update it. Thanks!

[Pete the Builder]

It's done. Anyone who would like to help by verifying my schematic please contact me by PM, and I'll provide the schematic. If you don't have the other schematic, it's available "in the wild". Beware of imitations!

FYI, There Be Dragons. The legality is all up in the air at the moment, but you may risk serious legal action if you choose to get involved. Sorry, I don't understand it fully myself, and I don't make the rules. Enter At Own Risk. Beware Of The Dog. Trespassers Will Be Composted. Etc.

Goody, now I can start the UPIM switched-cap daughtercards, which is what I was doing before I got interested in the other design.

Oh, yeah, there's no PCB yet. One thing at a time. My brain hurts right now.

And the banker's been. Looks fantastic (woo hoo!) but it can take up to 5 days before we know whether or not the bank's going to give us the opportunity or not. Fingers crossed.

Now, back to illuminating someone else's better design. I do feel like a 11th century monk highlighting and illuminating things he doesn't fully understand... but working with the schematics helps!

[Pete the Builder]

I've done something!

For anyone watching, I've just unraveled the coil/preamp schematic. It's attached below.

I've got a PCB design in the works, just roughing things out right now, so if anyone smarter than me (i.e. pretty much anyone at all) could cast an eye over the schematic and post any issues here, that would be great. This was a complete mind****, the lines connecting the inputs of the two op-amps started to merge into one... I don't know how many times I wired up the wrong pin 2 to the wrong pin 6! Argh! And the resistors! Aaaaah!

I've posted the original schematic as well, just to have all the material in a single place.

At this stage, I'm again working on a double-sided PCB, with all through-hole components (THCs - hee hee). If someone is desperate to not have a top-quality board to play with once the design is finalised, I might be able to actually do this single-sided.

And if anyone wants to use BW's original PCB, of course I would be happy to regenerate that as well as a .pcb file for future generations! Just say so.

I hope this gives a little kick forward into BW's brain before he made the Q-know-what...

Questions, comments, and suggestions welcome. Money, too.

-PtB
P.S. Boy oh boy the latest Adobe flash update is playing havoc with the attachment manager and uploader. Took me 4 tries before it worked. God I hate flash...
First, the original :
PtB Slot Board - Coil Schematic.pdf
Next, the updated version :
CS 2013 Coil & Preamp.pdf

[Midas]

This first attempt is a double-sided board, and it probably needs to be manufactured, unless you have experience with making double-sided boards. I've got a quote, for just one board on it's own is about US$70. That's the minimum, and I'll be making at least one for myself. Subsequent boards are much cheaper - for example, if 6 people want one, the full cost per person is US$25.00 That's for a solder-masked, silk-screened, through-hole plated, double-sided FR4 1/2oz copper board - better quality than anyone can hand-make. But it IS doable, if you've got experience. I've tried to minimise double-sided traces where possible.

http://www.seeedstudio.com/depot/fus...html?cPath=185
I've used these guys with good results. Only $30 for TEN 100mmx100mm double sided, through-hole plated, silk screened, delivered. I couldn't even buy the materials to make ONE board for that price locally, and of course even if I did it as you say, it would be nothing like the quality. $3 a pop, gotta love globalization.

Midas

[sido]

http://www.seeedstudio.com/depot/fus...html?cPath=185
I've used these guys with good results. Only $30 for TEN 100mmx100mm double sided, through-hole plated, silk screened, delivered. I couldn't even buy the materials to make ONE board for that price locally, and of course even if I did it as you say, it would be nothing like the quality. $3 a pop, gotta love globalization.

Midas

Hi Midas, that is a great price/per devolpment board...Have been looking local here in Au and does not come close to what you have posted. Very thankfull.
Will keep that in mind.

Cheers Sid