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wire wrap advice

Discussion in 'Electronic Design' started by [email protected], May 18, 2005.

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  1. Guest

    I want to do make some prototype microcontroller boards with an 8051,
    memory, latches, ... I think there will be about 10 ICs. I am new to
    wire wrapping and need to purchase the tools, wire, and prototyping
    board.

    Can someone give me advice on what tools, prototyping boards to use?

    Also best practices advice would be nice. I realize the importance of
    decoupling caps, but what about things like:

    choosing boards with ground planes, power buses, and connecting power
    and ground pins.

    what wire gages to use. Same for power, ground, and signal?

    Any tricks for connecting data and address buses?

    Specific manufacturers and part #s for tools and boards would be great.

    Thanks in advance,

    Scott
     
  2. Tim Wescott

    Tim Wescott Guest

    By the time you spend enough to be up and running efficiently doing wire
    wrap you will have spent enough for your first two quick-turn 2-layer
    prototype board designs -- and soldered boards are much better than
    wire-wrap.
     
  3. Luhan Monat

    Luhan Monat Guest

    Wire wrapping is a good choice if you are not very experienced.
    Microcontrollers, unlike microprocessors, are very forgiving on layout
    and such since rom and ram are internal.

    Wire up all the power and ground lines first. Run redundant connections
    in a 'matrix' manner. Put some 0.1 or so ceramic capacitors in several
    places spaced around the board and tie into the power and grounds.

    I use #30 wire for everything. Pad-per-hole boards allow you to solder
    two diagonally opposite pins on DIP sockets to hold them in place.
    Quarter watt resistors can be trimmed, bent, and inserted into DIP
    sockets. The same for small capacitors.

    Most all of the projects shown on the site below are done in wirewrap.
     
  4. Guest

    I hate to disagree with you Tim but a small project like this is ideal
    for wire wrap. The whole job would take only 2 hours or so to do once
    the circuit has been designed. Reliability is also good, wrap joints
    are good for at least 10 years allthough I have 20 yearold boards that
    still work fine.
     
  5. dave garnett

    dave garnett Guest

    I'd advise using a protoboard with a collander ground, and soldering
    ground pins directly to it. You will save yourself untold trouble !
    Similarly you can solder your decoupling caps directly between ground
    and the Vcc pin.

    Lots of colours will help you follow wiring more easily. You used to be
    able to get little labels which pushed onto dips and gave you the pin
    numbers - saves hours of counting.

    Another useful tip is that there are two sorts of wire-wrap wire -
    tefzel and kynar insulated. Kynar is tough, resists soldering irons and
    so on - but a pig to strip. Tefzel is easy to strip and not very robust.

    If you buy a 'cut strip and wrap' bit they only work with Tefzel.

    Go for 'modified wrap' tools (adds a couple of turns of insulated wire
    at the start of a wrap, gives greater strength to a joint).

    Your bus wiring strategy needs to take account of the fact that you get
    a limited number of joints on a single pin - three typically, unless you
    go for short pins.
     
  6. Paul Burke

    Paul Burke Guest

    As one who has done a lot of wirewrapping in my time, my advice would be
    not to do it. Prototype PCBs are now much more cheaply and quickly
    available than in the past, and you are unlikely to get bad wraps or
    signal problems. Wirewrapping gear is expensive, the less expensive the
    slower it is. Use a simple free PCB package, go to PCB Pool or PCB Train
    (in the UK- local alternatives otherwise), and you are also free to use
    SM components in the design without clumsy and terrifically expensive
    adapters.

    I still use it occasionally if I need a one off very simple (slow,
    coarse analog or single- chip microcontroller) test circuit in a blazing
    hurry, but then I've got all the gear lying idle already.

    Paul Burke
     
  7. Luhan Monat

    Luhan Monat Guest

    Since I've been doing it so long, I forgot to mention. Use precut and
    stripped #30 Kynar wire in a variety of colors. I buy them with a
    different color for each length. Using a standard 'modified wrap' tool,
    you can actually get about 5 wires on a '3 level' wirewrap socket. If
    you need more, cut off up to half of the 1 inch bare end, 5 turns of
    wrap is plenty good most of the time - thats a total of 20 contacts.

    The big advantage of wirewrap over circuit boards, is that is both good
    as a prototype (allowing experimentation and changes), and works as
    reliably as a soldered board (some claim more so), over long periods of
    time. I have never seen one fail - even after 30 years.

    Good luck,
     
  8. Guy Macon

    Guy Macon Guest

    Good asvice. Use a small clip-on heat sink to stop the solder from
    wicking up the pin.
    Find them here:
    http://www.action-electronics.com/pdww.htm#Id
    http://www.wassco.com/socketwrapid.html
    http://www.abra-electronics.com/catalog/sockets/8id.html

    Another tip: if you are connecting many pins together and go 1 to 2,
    2 to 3, 3 to 4, 4 to 5, 5 to 6, you end up ripping the whole thing
    out when you discover that 2 is in the wrong place. If instead you
    go 1 to 2, 3 to 4, 5 to 6 then 2 to 3, 4 to 5, you only have to redo
    three wires to correct an error.
     
  9. Guy Macon

    Guy Macon Guest

    In my opinion, this depends a lot on your experience. If your skills
    are such that the circuit is right the first time, buy a PCB. If
    your skills are such that you end up rewiring again and again as you
    learn, use wire wrap.
     
  10. Ken Smith

    Ken Smith Guest

    For most things, the soldered prototyping PCB patterns are a better option
    than wire wrapping. With the soldered stuff, the board ends up larger in
    the horz dimemsions but thinner. All the connections are made on the
    component side so there is no constant flipping of the PCB.

    Some years back DEC made (had made for them) a wire wrapped socket where
    the pins came up on the component side. This made for very easy wire
    wrapping.

    I prefer a hand wrapping tool to an electric gun. In the hands of a
    skilled person, the gun is very fast but it takes more care to use.

    There are wire wrap pins you can force or solder into hole of the board.
    These make very good tie points to help connecting things up. Power and
    ground connections often need extra tie points.

    Extra tie points can also be used to modularize the circuit. If the
    system breaks naturally into sections, making the connection between
    sections via a row of pins can help to keep the changes managable when a
    fault is found.


    Buy good quality sockets. Cheap sockets are a false economy.

    You want to run your power and ground wires as a grid. Each chip should
    have a bypass of a 0.01 or 0.1uF. Line driver chips should have two
    bypasses, one pointing North and the other pointing South so that they
    connect to two different ground runs.

    Twisted pairs of wire wrap wire are a good way to carry a sensitive signal
    from place to place. It can also be helpful if you have a bus such as a
    data bus and command signal running near each other.
     
  11. John  Larkin

    John Larkin Guest

    My advice: don't wire-wrap. If your time is worth anything, you'll
    come out way ahead laying out a PC board and having four or so fabbed
    by AP Circuits or somebody for less than $100 total.

    You said "some boards" not just one. There's nothing more tedious than
    wrapping the same thing multiple times.

    John
     
  12. Luhan Monat

    Luhan Monat Guest

    Wire-wrap the first one. Make sure it works. Have boards made for the
    rest (http://www.expresspcb.com}. Reworking PC boards is also tedeous.
     
  13. John  Larkin

    John Larkin Guest



    Design it, think about it carefully, and fab boards. It's good
    discipline for real life. We never breadboard entire circuits; we go
    directly to multilayer PCBs, and most of them are sellable first pass.

    Breadboarding teaches a number of bad habits. Careless design is
    self-reinforcing.

    John
     
  14. Luhan Monat

    Luhan Monat Guest

    Hey, I've done that for purely digital circuits. For analog and mixed
    signal stuff, no way!
     
  15. Terry Given

    Terry Given Guest

    hear hear!

    Its amazing what a good production department can do with rework :)

    a contract mfg we used in NH showed us a rework they did for one
    customer, who forgot a wire under a 512-pin BGA. So these guys (alas,
    cant remember name) whipped the BGA off, re-balled it, soldered a dangly
    wire onto the BGA then replaced it on the PCB. 100% success rate, almost
    1000 boards. wow.

    an OEM ups I got lumbered with had 90 rework mods. It took longer to
    rework the pcb than to assemble it in the first place. So we built
    17,000 like that :) [long story why we didnt re-spin the pcb]

    careful design + careful spice + careful layout = its close enough to
    working that we can make it go.

    Cheers
    Terry
     
  16. John  Larkin

    John Larkin Guest

    Oh, come on, take a walk on the wild side.

    John
     
  17. Luhan Monat

    Luhan Monat Guest

    Hey John, did you notice what the this thread is called???

    Game, set, and match.
     
  18. Rich Webb

    Rich Webb Guest

    Everyone has mentioned a modified wrap tool but nobody listed a specific
    one. Get the OK Industries WSU-30M (these guys have it cheaper than
    Digikey): http://www.web-tronics.com/wrto30awgmow.html for 30 gauge
    Kynar wire. I've had one for <cough-several-cough> decades and still
    reach for it occasionally.

    You can use pre-stripped wire but it's easy enough to cut and strip from
    a bulk spool. Use the tool above to do the stripping and use your finger
    joint as a quick'n'dirty gauge for the length to strip. Goes fast.
     
  19. Guy Macon

    Guy Macon Guest

    There are times when it is impossible to know what a circuit will do
    without breadboarding and modification. For example, I once designed
    a system that measured hydrocarbons in exhaust gasses by injecting them
    into a Hydrogen-Oxygen flame that contained two gold plated electrodes,
    applying 1,000 volts across the electrodes, and measured the resulting
    microamp current. I didn't know how many stages of filtering I would
    need to handle turbulance and still meet the response spec until I did
    a handwired prototype and took some measurements.
     
  20. Richard H.

    Richard H. Guest

    Hmmm... double-ended?? That'd seem awkward to spin one-handed.

    I got one of these when Radio Shack still had vacuum tube testers
    in-store... it still works great.
    http://www.radioshack.com/product.asp?catalog_name=CTLG&product_id=276-1570
    The head spins freely, making it pretty low-fatigue to use one-handed;
    stripper stores in the handle. It looks like they still stock it
    in-store too.

    Richard
     
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