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Thread: New Hardware Developer - Putting lights on your homenetwork!

  1. #21
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    Default Re: New Hardware Developer - Putting lights on your homenetwork!

    I know that the PCB was for an older proto, but a few suggestions:

    - Don't run any traces under the optos; the spacing is needed to keep the isolation barrier
    You could rotate the current-limiting resistors and run the ground trace between their legs
    - Grow the width of the ground traces to the crystal caps and decoupling caps. Traces to the decoupling caps need to be short and wide for low inductance
    - I don't see any decoupling caps for the PIC
    - Try to avoid 4-way junctions like the two on the left sides of R17. Having connections like that which are intentional makes it easier to overlook ones that are accidental. Not so important on tools like KiCAD which won't let you short two nets, but ExpressPCB has no checks to prevent this.
    - There's an acid trap on the trace between CN5pL and the bridge

    /mike

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    Default Re: New Hardware Developer - Putting lights on your homenetwork!

    Quote Originally Posted by n1ist View Post
    I know that the PCB was for an older proto, but a few suggestions:

    - Don't run any traces under the optos; the spacing is needed to keep the isolation barrier
    You could rotate the current-limiting resistors and run the ground trace between their legs
    - Grow the width of the ground traces to the crystal caps and decoupling caps. Traces to the decoupling caps need to be short and wide for low inductance
    - I don't see any decoupling caps for the PIC
    - Try to avoid 4-way junctions like the two on the left sides of R17. Having connections like that which are intentional makes it easier to overlook ones that are accidental. Not so important on tools like KiCAD which won't let you short two nets, but ExpressPCB has no checks to prevent this.
    - There's an acid trap on the trace between CN5pL and the bridge

    /mike
    And that is the exact type of advice I was hoping for by coming here. +1

    Thanks!

  3. #23
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    Default Re: New Hardware Developer - Putting lights on your homenetwork!

    Quote Originally Posted by n1ist View Post
    - There's an acid trap on the trace between CN5pL and the bridge
    I've read the descriptions (always trying to learn more), and this one has me stumped. What's an "acid trap", and where exactly is it in this diagram?
    Standard Disclaimers apply:
    "Product may not appear as shown, your mileage may vary, I'm not a doctor nor do I play one on television, these are not the droids you seek"

  4. #24
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    Default Re: New Hardware Developer - Putting lights on your homenetwork!

    Quote Originally Posted by LabRat View Post
    I've read the descriptions (always trying to learn more), and this one has me stumped. What's an "acid trap", and where exactly is it in this diagram?
    It's where the thin trace and thick trace join just to the left of the N pin on CN5, where the non-trace area comes to a sharp point. That very pointy area is a place where acid could get trapped when etching the board, possibly resulting in the thin trace being etched all the way through. I'm not sure this is a problem with modern fab houses, though.

    @Ike - what is that circuit around IC5 and IC6? I assume it's the zero-crossing circuit, but it's a little bit different from what I'm used to seeing. On the basis of n1ist's comments I'm assuming that IC5 is a full-wave bridge rectifier and that IC6 is a standard transistor-output optoisolator (like the 4N35, but in a 4-pin package). Could you have used an H11AA1 in place of those two parts?
    Phil

  5. #25
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    Default Re: New Hardware Developer - Putting lights on your homenetwork!

    Quote Originally Posted by P. Short View Post
    @Ike - what is that circuit around IC5 and IC6? I assume it's the zero-crossing circuit, but it's a little bit different from what I'm used to seeing. On the basis of n1ist's comments I'm assuming that IC5 is a full-wave bridge rectifier and that IC6 is a standard transistor-output optoisolator (like the 4N35, but in a 4-pin package). Could you have used an H11AA1 in place of those two parts?
    Yep, you nailed it. That's my original zero crossing detector I designed myself a while ago. I used that before I discovered the H11AA1 circuits commonly used around here. My newest layout which I hope to get made sometime this month uses an H11AA1.

    As for the acid trap, I haven't had a problem with it yet in the boards I have had manufactured to this point. ExpressPCB seems to be pretty clean with all the boards I have bought. That said, I think it would be pretty easy to send the smaller trace to the bottom of the board so I'll probably do that. Always good to play it safe.

    What PCB manufactures do you guys use? I've always used Express PCB due to the cheap $51 miniboard service but I want to explore my options when I move to the much more expensive custom size boards.
    Last edited by Ike; 02-29-2012 at 02:53 PM.

  6. #26
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    Default Re: New Hardware Developer - Putting lights on your homenetwork!

    CN5pL is just a shortcut for device CN5 pin L. As for board houses, I tend to use itead studio (seeed studio uses the same board house) but in the past have used PCBcart and Gold Phoenix. ExpressPCB is nice but I haven't used them since switching over to KiCAD. It's too bad they don't take Gerbers as input (the will generate them for $65 or so after you have fabbed a board thru them but that too is a bit pricy for home usage)

    I haven't seen over-etching problems with real board houses in quite a while (I have, however, on home-etched boards), but after getting yelled at for acid traps at work, I keep an eye out for them. I guess it is in the same catgagory as 90-degree bends.

    /mike

  7. #27
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    Default Re: New Hardware Developer - Putting lights on your homenetwork!

    given you have a microprocessor with the capability, have you thought of ditching the Zero crossing circitry, in favor of using one of the comparators on board for zero crossing? You can use that to drive an interrupt, and set your timing from there..

    Also, id look carefully at your decoulping around both your PIC and the ENC, i'd put both a 100 and 1nF in parallel, ( particually around the ENC ) as you will get some nasty HF transients flying around. Another thing you almost certainly want to do, is put some 'tank' caps on the board, ( >47uF ) near the main IC's.. They periodically pull quite high transient currents, and you'd be suprized how much this causes problems. You might also want to consider a slow start up on your PIC, so, that everything is stable before it starts ( use a cap and resistor tied to the MCLR to do this ).

    Perhaps you might like to post your schematic.. I've built a lot of stuff using this and closely related stuff ( the pics and the enc ) and probably can save you some disappointment

  8. #28
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    Default Re: New Hardware Developer - Putting lights on your homenetwork!

    Quote Originally Posted by mrpackethead View Post
    given you have a microprocessor with the capability, have you thought of ditching the Zero crossing circitry, in favor of using one of the comparators on board for zero crossing? You can use that to drive an interrupt, and set your timing from there..
    Simplest to use opto-isolators, I think. There are other possibilities, but anything directly connected to the AC is a bad choice IMO. It can be done, but a lot of attention has to be paid to isolation and safety issues, and (short of using a transformer to reduce the voltage), I don't think that these are good ideas for non-commercial or non-enclosed designs.
    Phil

  9. #29
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    Default Re: New Hardware Developer - Putting lights on your homenetwork!

    I was assuming ( badly ) that it was obvious that this would be the case. ( isolation ) whats not clear is how the device is powered, ( on the low voltage side ) i would have thought that it woudl have been derived from the AC.. In any case a schematic would clear that up... Something else i spotted that i think would be a good additon ( at no cost ) is a ICSP header.. Makes reprogramming and debugging much much easer..

  10. #30
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    Default Re: New Hardware Developer - Putting lights on your homenetwork!

    (test points for the SPI interface to the ethernet chip too... if you can find the space)
    Standard Disclaimers apply:
    "Product may not appear as shown, your mileage may vary, I'm not a doctor nor do I play one on television, these are not the droids you seek"

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