The issue with the regulator(s) came up early in the discussion. It will be best to leave the regulators off and connect USB externally with no 5V back into the board. That is why the design for the Centipede puts all these components on side break-out boards. I’m following this and redesigning Centipede to be an extension of Ant with all the “goodies” on the side. I hope we’ll come back to that one later.
I think the “convenience” resistors are important. It adds just about nothing to the cost, but does make the board self-contained. The principle should be to add all the components you will always use with the processor on board, and put optional components on the break-out pins.
Decoupling, reset pull-up, Special pins like Mode and Loader “not floating”, USB protection resistors and I2C pull-ups are considered mandatory in my book.
Just as an aside… Doesn’t I2C have internal pull-ups on the chip? Every other IO pin seem to have built-in pull-up or pull down?
Related question, because I was looking around for crystals in smaller packages, and I realized something:
Why does GHI use 27pf capacitors for the crystals? According to the datasheet, they should be either 18pf or 39pf, depending on the load capacitance of the crystal…
BTW, the price difference between the giant HC49 package used on the Mini and Panda II and a MUCH smaller package is roughly double, or ~$0.50 for the big one and ~$1.00 for the small one. The smaller package offers routing benefits.
Here’s what the routed board looks like with the much smaller crystal packages. As you can see, the traces are MUCH shorter, and this leads to better reliability for the crystals.
You know what I don’t understand? At RS Components, the small 32KHz crysta, 3.2mmx1.5mm is $1 in strips of 150 but $0.015 in bags of 5. Make sense of that…
I’m currently waiting for a test PCB to come back from DorkbotPDX. Assuming that goes well, I’m going to have a test run of 3 of my board made, as soon as I finish cleaning up the silkscreen. I’ll put together a final BOM here shortly. It won’t be very long, as I’ve gone and removed everything non-essential.
I’ve begun acquiring equipment to solder one together (just got my first real soldering station, yay!), since Gus made it look so easy. If anyone else is interested in one of the first run of the boards (understanding, of course, that they’re designed by a novice and completely unproven), I’d be glad to send them off at cost (which won’t be much).
@ godefroi - that’s why I asked! I’m interested in honing my as yet unproven SM soldering skills. I’d also be interested in starting a new Wiki page to create instructions for putting this board together, exchanging tips as we go. I’m not worried if there are glitches - that’s part of the learning process. I’ve already have a soldering “mistake” bin (with stuff in it) on my bench ???
hey fellas, i seem to be trying to jump on a moving train , but i am in the process of doing the same thing as you guys , just a couple of differences as far as chip and what pins i am breaking out and components etc… quick question though what fab-house will you guys be using? because some of the fab houses i have seen want to charge me more for a pcb then i would pay for a Domino , which i think is crazy, only half decent one is iteadStudio but turn-around time is insane being it is over seas. so i was just wondering if you guys have any other connections i may not… im the U.S by the way.
DorkbotPDX is here in the US, and the boards are manufactured in the US. They’re $5 per sq/in, but you get three copies. This board, which is 1.3"x2.5" will cost $16.25 for three copies, including postage, which works out to ~$5.42 per board.
Laen claims that you’ll receive your boards within 9 days of the order being sent out to the fab house. My order went out on the 26th, I’ll let you know when I get them back.
Depends on where you are in the US. I submitted my order for September 12 run. Got it September 27. Laen shipped it to me on September 22. I am in Virginia.
ithink it depends on when they get a full panel, i could place an order today but if that panel does not get full for another month then im out of luck and have to wait more , at least i think thats how they do it , sending a panel only half full would result in losses i assume.
DorkbotPDX are getting so popular that it’d be strange not to see their panels full in a fortnight. It used to be 4-6 weeks, it’s hardly that now from what I’ve seen.
The other options are all much longer lead times. They probably do the same thing, wait for a full panel before submitting to the China fab house. Seeed Studios and ITead Studios both have small run prototyping capabilities, but you end up with 10 boards (which might be good if you want that many). They have pre-defined sizes though so you have to pay for the full size based on what size your board fits into; you could try panelizing yourself if that was an issue.
yes their predefined sizes are good for some projects but can cripple you you in other projects. I will be sure to spread the word ,and yes a new thread would be nice for the 144 , i basically want to squeeze as much as i can out of the little bad boy.
I made a first pass at the BOM, sourcing the parts from DigiKey (except the important part, of course ;D)
The parts total comes to $24.24 plus about $0.50 per header if you want to populate the USB or JTAG headers.
The board, sourced from DorkbotPDX, runs $16.25 for a set of three (it is 2.5" by 1.3") or $5.42 per board.
As you can see, it would help a lot if the 1x24 headers could be sourced cheaper. I’m also eager to take suggestions or corrections on the rest of the parts.
Part Value Device Package Description
C1 27 pF C-USC0603 C0603 CAPACITOR, American symbol
C2 27 pF C-USC0603 C0603 CAPACITOR, American symbol
C3 27 pF C-USC0603 C0603 CAPACITOR, American symbol
C4 27 pF C-USC0603 C0603 CAPACITOR, American symbol
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=490-1413-1-ND $0.55 per 10
C5 .1 uF C-USC0603 C0603 CAPACITOR, American symbol
C6 .1 uF C-USC0603 C0603 CAPACITOR, American symbol
C7 .1 uF C-USC0603 C0603 CAPACITOR, American symbol
C8 .1 uF C-USC0603 C0603 CAPACITOR, American symbol
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=399-1097-1-ND $1.88 per 10
R1 15k R-US_R0603 R0603 RESISTOR, American symbol
R4 15k R-US_R0603 R0603 RESISTOR, American symbol
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=311-15KGRCT-ND $0.10 per 10
JP1 PINHD-1X24 1X24 PIN HEADER
JP2 PINHD-1X24 1X24 PIN HEADER
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A26509-40-ND $1.76 per 1
JP3 PINHD-2X3 2X03 PIN HEADER
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=609-3218-ND $0.43 per 1 (OPTIONAL)
JP5 JTAG PINHD-2X4 2X04 PIN HEADER
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=609-3362-ND $0.48 per 1 (OPTIONAL)
X1 32.768 KHz CRYSTAL-ABM8G ABM8G ULTRA MINIATURE CERAMIC GLASS SEALED SMD CRYSTAL
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=535-9166-1-ND $0.71 per 1
X2 12 MHz CRYSTAL-ABM8G ABM8G ULTRA MINIATURE CERAMIC GLASS SEALED SMD CRYSTAL
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=XC1770CT-ND $0.53 per 1
IC1 USBizi100 USBizi100 LQFP100
http://www.ghielectronics.com/catalog/product/117 $16.95 per 1
nice, is the text you posted straight from digikey’s BOM manager? I noticed BOM text files can be imported there, but have not investigated the exact format. Looks like were at about $48 each
That’s actually the BOM export from Eagle, edited somewhat. The crystal descriptions are wrong, because they’re just what I put in there when I created the part.
We’re actually at $29.66 plus shipping costs from Digi-Key. Probably there’s cheaper suitable caps available. Possibly there’s cheaper suitable crystals available. Hopefully there’s cheaper headers available.
If someone were planning to manufacture, say, 100 of these, costs would be reduced SIGNIFICANTLY.
For example, 100 decoupling capacitors can be had from Mouser for $1.60. That’d do 25 boards, and is less than the ones I have in the BOM above.
being it is over seas. so i was just wondering if you guys have any other connections i may not… im the U.S by the way.