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Printable RC Filter

by CafeT, published

Printable RC Filter by CafeT May 5, 2010

Description

In line with my desire for a 3D printer like the CupCake that uses conductive build material, here is a printable RC filter. The two spirals are a resistor and a capacitor. As you might have noticed, one of the spirals is continuous (the resistor) and the other has a gap in the center (the capacitor). Use of the circuit is just a matter of attaching power or a signal across the two thicker terminals perpendicular to the line formed by the spirals. This kind of circuit could probably be printed with traces on a PCB. Made in Inkscape and Blender.

http://makezine.com/go/makerbot

Recent Comments

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20% carbon black (by mass) into PLA (or PLC) yields a very conductive polymer (~0.09 Ohm/meter through 3mm filament), printed as an RLC resonant tank will be most interesting... any guess at this R(L)C behavior is suspect at best. Experimenters hoe!

I made a much longer resistor at thingiverse.com/thing:3029 with resistance calculations.
I didn't calculate the values. I just know from experience the sort of effects you get from PCB traces.

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Instructions

This is a 2D design extruded so it has volume. The block underneath is just to support the thinner sections. Ideally, the block would be dielectric/plastic while the design on top would be conductive.

20% carbon black (by mass) into PLA (or PLC) yields a very conductive polymer (~0.09 Ohm/meter through 3mm filament), printed as an RLC resonant tank will be most interesting... any guess at this R(L)C behavior is suspect at best. Experimenters hoe!

If you print it in copper R will be a fraction of an ohm and C will be only 10's of pF. That would give a time constant of the order of 1ps. At those sorts of frequencies the parasitic inductance and transition line effects would dominate.

I don't see any practical use for this.
How did you calculate resistance and capacitance? I was going to make it parametric (wrt these values) anyway, and that would help a lot.
I didn't calculate the values. I just know from experience the sort of effects you get from PCB traces.
I made a much longer resistor at thingiverse.com/thing:3029 with resistance calculations.
Printable Resistor
by CafeT
I didn't make this with a a scale in mind. Thanks goes to clothbot for doing that. I was just demonstrating creation of components and hoping someone else would be able to do more of the electronic engineering to make it useful. :)

Also, parallel plates in 3D is an obvious capacitor building method...
Neat idea!

The STL came out empty for me so I converted the SVG to DXF and whipped up an OpenSCAD wrapper to make something scalable to test later: thingiverse.com/thing:2982

You can't print conductive material yet, but there's nothing to stop you using the squeegee method to fill the trace with something that is!
Printable RC Filter Redux
Now we just need someone to make a software that can determine the values of R and C with a given geometry and material, so we can print the filters we actually need... ;)
Have you considered this approach:

chem.utoronto.ca/staff/WHEELER/Papers/OnDemand.pdf

This paper is about microfluidic applications, but if you want to print circuitry that's where I'd start... We used a colour printer to print a mask (using regular inks) directly onto copper sheet and then etch. Passing the copper sheet through the printer seems a bit...counterintuitive...but we didn't have any problems (YMMV, always possible it could blow up or injure you so be careful ) :)
CafeT - in reply to MarkU
Good suggestion, thanks for pointing that out. I like how they can control thickness, too, have to read the paper in full later. If I had that I'd have been more careful about calculations, practicality, etc.
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