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.
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.
------------------------------------------- Tim Wescott Wescott Design Services
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.
--
Luhan Monat: luhanis(at)yahoo(dot)com
http://members.cox.net/berniekm
"Any sufficiently advanced magick is
indistinguishable from technology."
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.
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,
--
Luhan Monat: luhanis(at)yahoo(dot)com
http://members.cox.net/berniekm
"Any sufficiently advanced magick is
indistinguishable from technology."
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.
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.
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.
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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.
Good asvice. Use a small clip-on heat sink to stop the solder from wicking up the pin.
Find them here:
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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.
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.
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.
True. Sometimes we breadboard a small circuit, like an oscillator or a GaAs fet switch, or we lay out a little board to test a part when the datasheet isn't clear or entirely believable. For example, we use a lot of microwave parts in the time domain, where there's little or no data. But there's no point in breadboarding an entire product, or even part of one, when the elements are understood and when the datasheets are clear.
Straightforward analog and digital and uP circuits will just work if you're careful. Breadboarding is a pernicious habit that encourages sloppy thinking and can let a lot of bugs and marginal designs sneak through to production. The Space Shuttle took off under full power, with a full crew, and flew to orbit on its first powered flight. The A380 took off and flew at altitude for hours, first time off the ground.
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):
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for 30 gauge Kynar wire. I've had one for 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.
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.
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