Electronics > Projects, Designs, and Technical Stuff
Digital Caliper with custom plates?
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q12:
(Mention and give credit to"q12" if you are doing this project and post it on internet)



{
This is an image from internet - not mine.
On my caliper, I peeled the plastic cover a bit in the margin, (the unused side), and the copper shapes are exactly like this image i put here from internet. Excellent.
The copper shapes are T's and I's. No connection between them. Just 'floating' shapes delimited by space/gap.
the fixed    plate circuit color is the brown one.
the mobile plate circuit color is the green one.
}

 The model circuit  is like this:  copper + space + copper + space +etc.
1.  My plan, how i see it from my intuition so far, is to unite Not in a straight line, but following the contour of the space between the copper shape. And 'voila', i extended it like that.
2.  If by some motif i can't cut the board exactly in the contour of the copper shape, I cut it in straight line, and where the gap between fiberglass pcb boards unite, I stick/glue a shaped copper foil between the 2 boards. I will reinforce underneath pcb's with a metal plate the 2 boards anyway.
 Exactly for this reason, is best to experiment with this juncture first, before using the full scratched length of the plates - to avoid any errors.
3.  Make the desired length board from a non conductive material. Plastic, wood, fiberglass, glass, cement, molded resin, stone, rubber etc. Glue the cut copper shapes into their positions onto the isolator board. Stick a band of scotch over all this top surface for protection. A couple rows of scotch for being sure. It can be matte scotch, not transparent, either. The capacitance field will not be interrupted. 
4.  Copper erosion with an acid, the old way of etching ! I almost forgot about it. For those who don't know, you paint on top of the finish part you want to remain with a acid resistant paint, but easy to remove after. We used special markers and before them, fingernail paint which we remove it with diluant or benzin/gasoline. Submerge the PCB plate into a bath of acid and check  from time to time until you see the white textolite surface underneath copper. Then is etched. Remove the paint to expose the copper trace that remained. (we used sometime fine sand paper and slightly remove the paint).
Merge more plates together using method 1 or 2 described here.

"I'm not sure how you will make them at home with required accuracy."
I am an artist by trade (digital and traditional painter). Patience is a requirement in my work. I have plenty.  Well, I did some sort of fine resolution modifications in my past and I am confident. Using a simple needle to do the scratching(if using copper plated PCB boards), it will give very good results, i am sure. But it will take a LOT of time!
Another idea is to buy some gold thin foil (used in orthodox iconography in this parts), and shape the required elements and glue them.
Of course, testing all the time, if it works and how it works. Making 1-2 cm length in the start until getting some results. If the results are ok, proceed to making the full length. Experimenting will take 1 week to 1 month or several months maybe, but actual building the full length will take a couple of days. Is how i predict it so far.

q12:
This is the gold foil I am talking about:
https://www.ebay.com/itm/100-Sheets-Gold-Sliver-Copper-Leaf-Leaves-Foil-Paper-Edible-Gilding-Craft-Decor/382556673030?hash=item5912279406:g:GZ8AAOSwDYBbjgSf:rk:5:pf:1&var=651312637216&frcectupt=true&autorefresh=true
@ $2.25

Here is more practical solution :  5mm Copper band. Why 5mm and not 6mm that you find a lot on ebay? My T shape copper element width is 5mm. So 1 side is resolved automatically.
https://www.ebay.com/itm/1-Roll-Copper-Foil-Tape-Single-Adhesive-Strip-For-Stained-Glass-5mm-Copper-Faced/323444613013?hash=item4b4ecd1f95:g:dVsAAOSwnTdaHmBa:rk:12:pf:0

Now, how to cut such thin material? And precise enough...
Practice i suppose.
If you have any ideas on this subject, please tell me.

1. I have a stone for knife sharpening. I sharpen my chirurgical knife with that stone, it was like a samurai sword cutting efficient. I cut a paper and some surface layer skin to test it. Also some hair from my arm. That can be used as efficient as possible.    Also using cutter blades is another solution.

2. I also wonder if there are some LASER cutter individuals, who can make the desired shapes from copper foil for me(us), put those shapes in a bag, mail it ... And I just pick and stick them. That will solve the precision cut problem. Mmmm, that will be awesome.
ataradov:
There is absolutely no way you will cut so many lines by hand with required accuracy. You may get it to show you something, but how are you going to prove that whatever is shows is accurate?

I don't want to stop you from trying, but I don't think any approach that requires cutting something by hand will work. You need to figure out a process to make this work in a more automated way.

If I was going this route, I would be exploring ways to accurately join two PCBs like this together, and then order a bunch of shorter boards from cheap manufacturers like AllPCB or JLCPCB. May be put vias on the edge copper panels and join them together on the back side. Not sure what this will do to the readings.

How cheap is your labor that you are willing to work for a month, and don't want to spend $50 on a readily available solution. You know you can make much more than $50 in a month doing something else?
q12:
Thank you for believing me, mister ataradov. I will be forced by life to change work very soon, but until then, I will endure a bit more. I resisted 6 years already. Not the place here to discuss such things. But I appreciate.
Again, you are right about automation as a safety measure against (manual) errors.

"- how are you going to prove that whatever is shows is accurate?" - I will draw a measured ruler on the table and I will slide the thing against it for comparison. Smart,da?

I will have to actually start doing some tests. I am agreeing with all that you said, and all that we discuss here is standing in the back of my mind. But experience will teach me the truth. Probably  I will fail as you predict and I am not that a large hope myself... i'm rather curious about the thing. Very ! And that's all that matters. I will update here the results, bad or good, to leave a nice finish.
 Again, your advises were very direct and to the point. Don't change! Thank you.
Conrad Hoffman:
Here's another way to do it using a tube of precision balls, something that better lends itself to DIY- http://www.newall.com/technology/
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