Vik has tried an experiment with his circuit idea. He says:

"I did a quick experiment with conductive silver paint. I Stretched out commercial PVC food wrap over a box lid and daubed tracks 1.5-2mm wide on it. When the paint had cured, EVA hot-melt glue was applied to cover the tracks in an approx. 0.5mm layer.

"Spare component leads were pushed through the PVC into the EVA via the paint. A resistance of 0.6 ohms was measured across two test leads inserted into circular pads at each end of a 25mm line.

"The pen tip is not a fibre tip, but reminiscent of the old correction ink pens, and the particular one I had was prone to clogging. A syringe-based system may be more appropriate.

"I'll leave the samples for a week and see what happens to them. If all is well, I'll attempt to assemble a simple electronics kit. This should be achievable by stretching the PVC over the copper side of the board,
tracing out the tracks, and pushing the components through. I might mount that one on drilled plywood though."

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Here is the latest Wood's metal deposition head design from Ed Sells, all made by RP:




(To see the original look at the blog for March 23 2005.) This one has a hot-air heating jacket controlled by a thermocouple thermostat, and drive feedback from the optoswitch you can see at the top of the picture. The whole thing is straightforward to control with a PIC and the rather neat H-bridge BA6286 from Rohm. When I can get myself (and more importantly the data) organised I'll put all the designs and software up on the Documentation section of the website.

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Thanks to my colleague William Megill for drawing the following measuring device to our attention; he says:

"It's basically two thin copper wire coils set in a sleeve of silicone rubber. As it's stretched, the coils get further apart, which changes the capacitance. Strains up to 150-200% are no problem."

See this link for details.