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Opinions on design requested

Discussion in 'Electronic Design' started by HighFlight, Nov 4, 2003.

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  1. HighFlight

    HighFlight Guest

    I'm a novice and this is my first attempt at designing a PCB. If you don't
    mind, could you give me some feedback on the feasibility of my design.

    Also, suggesting on the resistors and LED's would be incredibly helpful.
    The 5v voltage regulator design I'm stealing from the current board. It is
    outputting a clean 5v. I'm planning on breadboarding the design...but a
    starting point would be awesome.

    The background is that this a 12V (boat) light control. The current one
    doesn't work and I wan to replace it with a simpler design. I'm using a
    P227EE1C DPST push button switch but still trying to keep the "cute" LED
    indicators.

    Any feedback is greatly appreciated.

    Thanks.

    Jon

    http://www.malenfant.us/ShoreThing/Lights
     
  2. Is there a schematic?

    What are the loads?

    What about the old design doesn't work?
     
  3. Leon Heller

    Leon Heller Guest

    It's not a good idea to have those acute angles where the tracks leave
    the pads and where tracks meet.

    Leon
     
  4. HighFlight

    HighFlight Guest

    No. I don't have any schematics. But the link I included shows the board
    layout, which is pretty simply I think. The lights use a common + and
    switched -.

    The loads are light. They are just small 12v, very low wattage each lights.
    Each circuit controls a single light (they used the shotgun approach to
    lighting the cabin).

    The current board kinda works when I first insert it. But after a few
    seconds, all the circuits shut off and never come back on. If I pull the
    board out, wait a few seconds, and put it back in, it works again for a few
    seconds. I though it might be a thermal problem so I replaced everything
    but the resistors...but the same thing happened. Can a resistor have
    thermal issues?

    Thanks.
     
  5. HighFlight

    HighFlight Guest

    I'm not sure where you are talking about. Sorry, although I can solder
    halfway decently, I got nutt'n otherwise. Could you give me an example of
    where you mean.

    Also, do you think with small 12v lights, that the switch is ok...and the
    design in general is ok?

    Thanks very much!

    Jon
     
  6. After sending my earlier reply I looked at the layout more closely and
    realized you were controlling each light with a switch and had a LED in
    parallel to show which light should be on. I'm guessing the F's are fuses.
    Why was the old board so much more complicated?

    If you are building only one of these, I can't see any problems with it, as
    long as you get the LEDs in the right way.

    For componenet selections, look in google.com. For 5V, and normal red LEDs,
    330 ohms usually is about right.
     
  7. Don't route a signal that has an angle less 90 degrees if possible.

    These are acceptable: | /
    | /
    ------- -------

    This is unacceptable: \
    \
    \
    -----

    The reason is that contaminents can get caught in the acute angles and
    corrode, possibly causing long term reliability issues.

    --
    +--------------------------------+----------------------------------+
    | George H. Patrick, III | Resources for PCB Designers on |
    | | the Web - The Designer's Den |
    | | http://www.pcb-designer.com |
    +--------------------------------+----------------------------------+
    | Take what you like and leave the rest... My opinion ONLY. |
    +-------------------------------------------------------------------+
     
  8. HighFlight

    HighFlight Guest

    Yup, I'm definitely only building one. I played around a little with the
    etching process and am going to give that a go. Should be interesting. I'm
    going to breadboard the circuit first. Thanks very much for the LED and
    resistor suggestions. I will start with that.

    The complications with the current board are just around the use of what I
    have come to learn are J/K flip flop circuits and MOSFETs. I tried
    re-creating the use the MOSFETs without luck. Switching the ground just
    seems odd to me...but what do I know! I guess they just wanted to be cute
    and use momentary switches. Heck...I just want it to work!

    Thanks again for your help.

    Jon
     
  9. HighFlight

    HighFlight Guest

    Ok...gotcha. The close angles were me just trying to take advantage of both
    sides of the switch. I figure two paths were better than one. Considering
    I'm going to etch it, I could just make it one solid area rather than making
    the 'V' shape.

    Thanks very much for the input.

    Jon
     
  10. Indeed, the more copper you can leave on the board, the faster your etching
    will go and (to massively oversimplify) the more current you'll be able to
    handle. There's really no reason to have a couple of traces on an otherwise
    bare board - it's probably better to have a couple of bare lines separating
    large areas of copper. Sometimes when you do it this way, you can just etch
    the bare spots with a Dremel tool or razor blade - you don't even need to
    use chemicals at all. A rendition of a simple board done this way is at
    http://www.cafewalter.com/cafewalter/fetpre/basspre2.htm.

    By the way, if you're going to etch this yourself, then you'll have a much
    easier time if you don't lay it out double-sided. Do it single-sided, and
    use jumpers where you have to. With a little bit of thought you can
    probably get it so that you need few if any jumpers; but even if you need a
    lot, it will still be a lot faster and easier than trying to get both sides
    of the board aligned and making sure that every via (the places where one
    side connects to the other) is actually connected.
     
  11. Jim Meyer

    Jim Meyer Guest

    1, Your 5 volt regulator, VR1, only has connections to two of its
    leads.

    2, The dropping resistors for the LEDs all connect to each other at
    one end, but then they only go to a capacitor. LED current will only
    flow while the capacitor is charging (brief flash).

    3, You really don't need to drop the 12 volts down to 5 volts just
    to run some LEDs. Use the 12 volts directly by raising the dropping
    resistors' values.

    Jim
     
  12. HighFlight

    HighFlight Guest

    1. Yeah, I was going to jump the lead in into the VR using a diode like the
    current card. I should have made a circuit diagram...sorry.

    2. Wow...I totally misread the current card. After your comment, and
    looking deeper, I realized the ground and output are jumped with the
    cap...which I then followed with "DUGH!". Thank you on that one!

    3. Well that would certainly make things less complicated. What size of
    resistor could I use? I have 10K, 1K, and 3.3K, and 330, and 220ohm
    resistors. Can they be strung together? Parallel or serial?

    Thanks!

    Jon
     
  13. HighFlight

    HighFlight Guest

    I took your advice and redesigned it to be one sided. It turned out to only
    need a few jumper. You are right, that will make the process much simpler.

    Thanks.

    Jon
     
  14. HighFlight

    HighFlight Guest

    Boy did I overcomplicate this. I found a site that helped and found the
    resistor. Much easier!

    Thanks!!!

    Jon
     
  15. James Meyer

    James Meyer Guest

    You are starting with 12 volts and the LED will subtract 2 volts all by its
    self leaving 10 volts remaining. If you use a 1K value for the dropping
    resistor, Ohms Law (V = I x R) tells us that you will limit the LED current to
    10 mA which should make the LED pleasantly bright. The 3.3K value will be fine
    if the 1K value makes the LEDs bright enough to keep you awake at night.

    Heck, with a few transistors and a photo-resistor, you could make the LEDs
    automatically get brighter in the daytime and dim at night.

    Jim
     
  16. HighFlight

    HighFlight Guest

    DING!

    Thanks to everyone who made suggestions. I have a simpler and cheaper
    design now between making it single layer and getting rid of the VR and just
    using between a 1K to 3.3K resistor for the LED's.

    My only other question is the switch. Is the
    http://rocky.digikey.com/WebLib/E-Switch/Web Data/P197 Series.pdf safe
    to switch the raw 12V source in the boat? I'm using 2mm traces on the board
    and it's switching ground with a fuse between the switch and the light.

    Thanks.

    Jon
     
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