Artificial Stupidity

Discussions around autonomous, semi-automatic and intelligent robots and systems.

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BeligerAnt
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Post by BeligerAnt »

You have 2 choices: DIY or pay someone to do it for you!

For the DIY method, you will need some PCB design S/W (free), access to a laser printer or photocopier, some "Press'n'Peel" film from Maplin (?15) or another method of transferring the toner (glossy photo paper, ohp film - search the web for various suggestions), some ferric chloride to do the etching, some plastic trays/dishes/tanks to do the etching in, and some old clothes because ferric chloride stains everything.

You can just use a permanent pen to draw the tracks onto the board, but this method only really works for large through-hole parts. It's certainly no good for surface-mount parts on a 0.5mm pitch!
You can also use a UV-sensitive solder resist and a light box with a track pattern printed onto OHP film, but this requires a UV light box. I think Peter Waller uses this method.

You also need some copper-clad board from Maplin, Farnell etc. Single-sided boards are dead easy to make, double sided gets a bit tricky ensuring correct registration of the two layers. I tend to use one side as a ground plane and the other side for tracks. Anything that's too difficult to route I use wire links.

I use the Press'n'Peel method which has worked very well for me for quite a while now.

You can now buy small quantities of prototype PCBs quite cheaply from a variety of suppliers. Try www.pcb-pool.com, www.pcbexpress.com, or www.pcb-train.com
I've not tried any of them, but I think Chris has used one for his SmartAnt boards. Costs are around ?30 for a 100x100mm or 160x100mm board. Some companies will let you fit multiple boards into their standard size, so if your board is only 50x50mm you will get 4 or 6 for the standard ?30 charge. Read the T & C's closely!
Gary, Team BeligerAnt
slurp
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Post by slurp »

BeligerAnt wrote:For the DIY method, you will need some PCB design S/W (free), access to a laser printer or photocopier, some "Press'n'Peel" film from Maplin (?15) or another method of transferring the toner (glossy photo paper, ohp film - search the web for various suggestions)
I use the waxed backing paper from a label sheet... you don't have the problem of soaking the paper off.

Press evenly over the back of the sheet and let it cool before peeling

Don't try to put the sheet thru the printer more than once, it's likely to crumple. Better to print all your masks in one go...

best regards,
colin
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Post by Andrew_Hibberd »

Thanks for the advice, i will look into this more. I have been using the eagle software, the trail version allows the design of two sided boards. I have planned it out to use double sided, but i have also planned one using strip board as it won't require etching. However i will look at making a single side board and have a few linking wires as this will be more space efficant than the strip board and will be easier to make than the double sided ones.

I am curious about the waxed backing paper, is this just the stuff left over on the back of stickers? If so would be cheaper than the press and peel film.

Thanks again
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slurp
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Post by slurp »

Andrew_Hibberd wrote:I am curious about the waxed backing paper, is this just the stuff left over on the back of stickers? If so would be cheaper than the press and peel film.
that's the stuff... just take you time and don't rush it :D

once pressed it's also worth rubbing the surface lightly to see what has not taken to the surface but a little care and you should be ok

there's a couple of picture here

regards,
colin
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BeligerAnt
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Post by BeligerAnt »

Some layout tips for home-etched boards:

1) Be conservative! Most CAD programs are aimed at commercial PCB manufacturing. They default to 0.012" (0.3mm) or less tracks and gaps. Whilst it is possible to achieve 0.012" at home, 0.020" is so much easier! Make life easy by using the biggest tracks and gaps you can. If you can get away with 0.1" pitch through-hole parts and 0.050" tracks and gaps it will be a breeze.

2) Beef up the pads! Again CAD programs assume some small drill sizes and often minimal pads. Small drills break very easily (so work out expensive) and small pads require very accurate drilling to avoid the drill breaking out the side of the pad. Oval pads can help if you need to get a track between 2 pads.

3) Especially beef up your vias! It's OK to use a 0.3mm hole and 0.5mm pad on a professional board, but for home building, stick to a sensible drill size (at least 0.8mm) and a decent pad (2mm is comfortable).

4) If your CAD program can do it, put a 0.020" (0.5mm) drill hole in the middle of each pad, and make sure it appears as a hole in the copper on the final print output. You will then have a centre help with the driling.

5) Use one side as a power and/or ground plane. It really reduces the number of connections you have to route on the signal layer, and gets rid of the longest net(s). If you use the plane for power and ground, use the CAD program to route both with no links. Then work out a route between the tracks to cut the copper into 2 areas. You don't need to etch the plane side, just cut along your route with a craft knife (Best done after drilling as the holes act as a guide).

5a) For through-hole, put the tracks on the bottom and the plane on the top. Components that connect to the plane can simply be soldered on the top side.

5b) For surface-mount the tracks need to be on the top and the plane on the bottom. You will need to make some via holes (use wire links) to connect to the plane.

5c) For a mixture of through-hole and surface-mount, put through-hole on one side and surface mount on the other. I usually put SMT on the top as that's what I use most of. Make sure you "mirror" the components correctly when putting them on the bottom side.

6) If using a power/ground plane, don't forget to mask the plane side when etching the signal side! Ordinary masking tape works fine, make sure it is well stuck down and overlap any joints carefully.

7) Put some text on each layer, even if it's outside of the board outline. This way you can easily tell whether you've got the design round the right way! Don't forget text on the bottom layer appears reversed in the CAD program!

8) If using any of the "iron-on" methods, don't forget the pattern needs to be printed out in reverse. The text comes in handy here. If you are doing the bottom side of a board, you need to print it "straight" from the CAD program as it is already designed in "reverse" :o

9) Add some dimension lines to your design. You can then measure them to check that you really have printed out at 1:1.

10) Make sure you use at least a 600dpi laser printer, the old 300dpi ones are no good for fine PCB tracks. Even with 600dpi, don't attempt anything below 0.003" as it might not even print properly.

11) Don't use an inkjet printer, it won't work! :(

That's all I can think of for now, might stop you falling into some of the holes I had to dig myself out of...

(Colin, feel free to rip this for a "how-to" for your site :) )
Gary, Team BeligerAnt
Andrew_Hibberd
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Post by Andrew_Hibberd »

Thanks Gary that is very useful. I will do some modifications to my design. I suppose i will have to wait until i have access to a lazer printer before making the board.
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Post by slurp »

BeligerAnt wrote:(Colin, feel free to rip this for a "how-to" for your site :) )
Thanks Gary, what links would you like when credited for the text.

regards,
colin

after thought:
this might for some tips for a bigger piece on PCB etching in general...
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BeligerAnt
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Post by BeligerAnt »

Colin
Use the "www" button at the bottom of this post...
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Andrew_Hibberd
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Post by Andrew_Hibberd »

I have been working on the next version of artificial stupidity. I will be using 2 IR opponent detectors and 3 line sensors. Was planning to keep it simple but is getting more and more complicated. Will update when i have compiled the necessary parts.
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Post by BeligerAnt »

Glad you're still working on it Andy!
Orgiami is likely to remain mechanically unchanged for a while but I will try to find time to tweak the software before the next AWS.
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