Topic for #homecmos is now Homebrew CMOS and MEMS foundry design | http://code.google.com/p/homecmos/ | Logs: http://en.qi-hardware.com/homecmos-logs/
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<bart416> azonenberg, did you ever take part in a "design a DSP system in 4 hours" contest?
<bart416> We did yesterday
<bart416> Worked amazingly well :S
<azonenberg> Design a DSP system in four hours? No
<azonenberg> I'm currently in the middle of a self-driven "design a pipelined superscalar DSP softcore in 4 months" contest :p
<bart416> We used a 8 bit flash ADC heh
<azonenberg> lol
<azonenberg> oh, check out this board http://i.imgur.com/sZng0.png
<bart416> Not much that can go wrong there
<bart416> And DACs generally well behave
<azonenberg> my first design in kicad
<bart416> Not bad
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<azonenberg> the TQFP is the ethernet PHY/MAC
<azonenberg> the MCU is the little QFN at left
<bart416> I figured out it was RJ45 due to the connector pattern :P
<azonenberg> jack is 10/100 with integrated magnetics
<azonenberg> so two center-tapped transformers
<azonenberg> all contacts are SMT
<azonenberg> The only through-hole component on the entire board is the JTAG header
<azonenberg> the footprint at left (no 3d model) is a mini USB
<bart416> You sure?
<azonenberg> Yes, but i just realized i did osmething dumb
<bart416> Looks an awful lot like the footprints for network connectors lol
<azonenberg> *reopens kicad and fixed bad footprint*
<azonenberg> its small :p
<azonenberg> let me put it this way, the giant header at the bottom is 0.1" pitch
<bart416> lol
<bart416> Let me put it this way, my latest board is A4 sized xD
<azonenberg> lol
<azonenberg> How many parts on it?
<bart416> roughly 200 BJTs
<bart416> 700 resistors or so
<azonenberg> ...
<bart416> 2-3 inductors
<azonenberg> is this your RTL monster?
<bart416> part of it
<bart416> lol
<bart416> testbench board
<bart416> 7 capacitors
<bart416> 10 voltage regulators
<bart416> 1 opamp
<bart416> (relaxation oscillator)
<azonenberg> o_O
<azonenberg> also... LOL good thing this is a batch board
<azonenberg> there's time to change it before it goes out :po
<azonenberg> just realized my pinout on the usb connector was wrong
<bart416> heh
<azonenberg> pins 4 and 5 got swapped somehow
<azonenberg> Nothign i couldnt fit with rework but it'd be annoying
<bart416> btw, yellow at the left is a capacitor right?
<bart416> yellow-beige I meant
<bart416> or is it a resistor?
<azonenberg> tantalum cap
<bart416> your track to it is rather small
<bart416> Might cause problems if it's for decoupling like I assume it is
<azonenberg> Yes, and also good catch
<azonenberg> All the 3.3V stuff is on a filled plane
<azonenberg> somehow the 5V rail got forgotten lol
<bart416> lol
<bart416> you getting the 5V from the USB?
<azonenberg> Yes
<azonenberg> Nothing high powered
<bart416> be sure to add diodes to protect the usb port from reverse current flow
<azonenberg> how would that happen?
<azonenberg> there's no external power source anywhere
<bart416> It's standard procedure on good designs
<bart416> It just happens
<bart416> I've gotten into the habit of adding diodes to protect my power rails recently
<bart416> And it has saved me a lot of trouble
<azonenberg> That'll go in the next board rev, i think
<bart416> There was a while I constantly had issues like my 0V going above my 5V in potential :S
<azonenberg> how is that even possible?
<azonenberg> I just have a linear reg and then everything else is 3.3
<soul-d> i hope n4148 orsomthing will do nice for that
<bart416> it happens if you operate a switched mode topology
<bart416> you build up charge
<azonenberg> Oh, i see
<azonenberg> Yeah, no SMPSes here
<bart416> And suddenly it ends up in places it's not supposed to go
<bart416> It's just, the cost of the diodes is so low that there is no point in really adding it for small home designs
<bart416> If you're making a run of 10000 then indeed it's worth checking if it's necessary or not
<azonenberg> Well, its more that i dont have any diodes handy :p
<azonenberg> So i think i'll leave them out this revision
<bart416> I bought this reel of diodes a while back cause it was really cheap and would push my order over the shipping fee limit
<bart416> So free shipping
<soul-d> bought 500 smd ones on last order should be enough to protect me from my stupidity
<soul-d> 3,25 euro for that
<bart416> And that was actually cheaper than the original order + shipping fee lol
<soul-d> did come from china though
<bart416> 2000 1Nsomethings lol
<azonenberg> A big load of schottky diodes is on my next parts ordrer
<azonenberg> but not in time for this board
<bart416> :)
<bart416> What's really funny is the cost to make an A4 sized board at university
<bart416> 10 euro >_>
<azonenberg> o_O
<bart416> I can't etch it myself for that price
<bart416> can't order it myself either for that price :S
<bart416> order it at morning, have it in your hands by late afternoon :S
<soul-d> how many layers
<bart416> double sided
<bart416> Didn't believe it myself at first either :S
<soul-d> so you pretty much pay cost price of pcb
<bart416> ofc you don't get a soldermask or anything
<azonenberg> bart416: yeah
<bart416> just an etched pcb
<soul-d> not drilled either i geuys ?
<bart416> But that's not really all that bad all things considered
<bart416> Nope, not drilled
<azonenberg> Oh
<azonenberg> i'd homebrew then
<azonenberg> i send out boards for things i cant do at home
<soul-d> do you predrill azonenberg ?
<azonenberg> Like PTH
<bart416> You can throw it in the CNC drill in the lab azonenberg
<bart416> Give it 5 minutes...
<azonenberg> soul-d: I havent gotten plating to work yet
<azonenberg> bart416: its not the hole drilling, its the plating
<azonenberg> In any case the best price i've seen yet for full-service fab is dorkbot's batch service
<azonenberg> there is long lead time
<soul-d> drilling is nasty work to do manual
<bart416> For through hole I can't say their board quality is bad
<azonenberg> But $5/in^2 for three units
<bart416> We've used it for loads of projects
<azonenberg> or $10/in^2 for quad layer
<azonenberg> three units
<soul-d> you checked out seeedstudio azonenberg ?
<bart416> power or signal layers?
<azonenberg> bart416: fully routable
<bart416> sweet
<bart416> soul-d, seeedstudio is good if you do larger batches
<bart416> I intend to do it for my final design as the core components will always be the same
<azonenberg> soul-d: we're talking prototype volumes here
<soul-d> ok yeah i would like a palce for that
<soul-d> i usaly need 2 boards at most
<bart416> The thing is, you can't homebrew an A4 sized board for that price
<azonenberg> Also
<bart416> I often etch PCBs for other people
<bart416> can't make it for that price
<azonenberg> seeed doesnt seem to provide quad layer
<azonenberg> I actually want to try to find a cheap place for prototype volume 6 or 8 layer boards lol
<azonenberg> Because when i get into designs that use stuff like 484-ball FPGAs and multiple banks of DDR3
<azonenberg> They get pricey :p
<soul-d> plus you probably want to outsource soldering id would find that tricky :P
<azonenberg> Not sure about that yet
<azonenberg> Depends on how well my first BGA board goes
<azonenberg> Only two metal layers
<azonenberg> 6x6mm CSBGA CPLD, 56 balls
<azonenberg> broken out to DIP-pitch headers and a JTAG port
<azonenberg> For scale the caps on the underside are 0402
<soul-d> :)
<azonenberg> And the traces are 6 mil / 150um
<bart416> soul-d, do you etch your own pcbs?
<soul-d> id be happy if i design somthing with 0805 and some tqfp do have some qfn's around
<soul-d> do have stuff laying around
<azonenberg> soul-d: I used to do 0805 and 0.8mm TQFP, moved very quickly to 0603 and 0.5mm
<soul-d> but not complete drill set :)
<azonenberg> But now i want to take the big leap
<azonenberg> into more "hardcore" packages
<azonenberg> BGA, QFN, 0402
<bart416> bga is annoying
<azonenberg> I know it is
<azonenberg> But a lot of the really cool parts dont offter any alternatives
<azonenberg> this CPLD does come in both TQFP and QFN
<bart416> yeah :(
<bart416> It's a pest
<azonenberg> But i got the BGA version because it's $1.60 a chip
<azonenberg> so i can afford to kill several while refining my reflow process :p
<bart416> I'm looking for some time on the university's pick and place machine at this point actually
<azonenberg> And not kill a $25 FPGA
<bart416> The machine only has an error rate of 1 in 1000 or something like that heh
<bart416> Can't do that at home
<bart416> azonenberg, why don't you use the university's machines over there to do the BGAs?
<bart416> I'm sure they have some
<azonenberg> bart416: I'm not trying to build a board per se
<azonenberg> i'm trying to develop a process that i can take with me after i graduate
<bart416> heh
<azonenberg> I may use their gear the first time, to get started
<bart416> Here they keep doing it for old students
<azonenberg> but i want to avoid being dependent on them
<azonenberg> I may not be living anywhere nearby
<bart416> Some guy consulted a professor this week (was working in the same lab at the time) on how to build a computer using vacuum tubes btw :')
<azonenberg> lol
<soul-d> you did that bga in kicad to ?
<bart416> The professor started laughing at the guy lol and told him to go and get a life
<bart416> (keep in mind this is an old guy from the vacuum tube era that is an expert at high frequency design as well, so he's used to things being hard or near impossible to make)
<azonenberg> soul-d: yes
<bart416> How good is kicad at bgas?
<azonenberg> bart416: So far? Decent
<bart416> You sure?
<azonenberg> I need to play more, obviously
<azonenberg> But it handled this little guy just fine
<bart416> The only program I've found good at auto routing them is orcad/allegro at this point
<azonenberg> Oh, this was hand routed
<bart416> ah
<soul-d> does anybody acrutaly do autoroute ?
<bart416> yes
<bart416> Altium and Allegro can do it
<soul-d> yeah started that stuff up once i din't realy get it :P
<bart416> You can write an entire book on how to use those auto routers lol
<bart416> They're also capable of auto placing components taking into account design rules
<bart416> another thing eagle fails horribly at
<azonenberg> i've never tried doing something quite that complex lol
<azonenberg> my biggest board to date was in the 200 component range
<soul-d> i hate eagle every minitue i use it lol
<soul-d> im just stocking up on basic components for now
<soul-d> now im broke ofcourse
<bart416> I still find myself often just grabbing transparent paper and a marker and drawing the routes by hand...
<soul-d> i probably make to may mistakes for that
<bart416> It's good enough for small boards
<bart416> You should try it once azonenberg
<bart416> works great for high frequency board as it's pretty much impossible to make sharp corners by hand :)
<azonenberg> lol
<bart416> azonenberg, you have some experience with this
<azonenberg> with what?
<bart416> What do you think about level triggered flip flops in digital design
<azonenberg> I've always worked with synchronous design so far
<bart416> Yeah, but I meant triggered on clock level instead of edge
<azonenberg> Oh
<azonenberg> hmm
<azonenberg> i'm so used to doing edge triggered stuff
* bart416 too
<azonenberg> never had the chance to fool around much
<bart416> I mean, I sometimes dare to use a regular RS flipflop in async design
<bart416> But I'm talking about an entire register bank this time
<azonenberg> Hmm
<bart416> The risk of unwanted triggering seems to be fairly high
<azonenberg> Yes, it does
<azonenberg> Yay glitches
<bart416> glitches on the clock are unlikely but yeah, glitches when clock is high...
<azonenberg> You'd be much more sensitive to skew
<azonenberg> if data starts changing before your clock falls
<bart416> yeah
<bart416> it's risky
<bart416> I'd have to buffer the input to the flip flops somehow
<bart416> I can use a S/H circuit for that I guess
<bart416> but that just seems stupid
<bart416> Btw forgot to mention, we had to make a guitar distort with our dsp
<bart416> so the 8 bit wasn't much of an issue
<bart416> the distort already destroyed so much information anyway that using 8bit wasn't a problem lol
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<berndj> bart416, not really tubes, but http://www.ese.upenn.edu/~jan/eniacproj.html
<bart416> berndj, not of much interest to me to be honnest
<bart416> I don't have this much space btw: http://upload.wikimedia.org/wikipedia/commons/4/4e/Eniac.jpg