Hello there again. I took three months off to travel but I am back in the swing of things with a couple of exciting engineering projects lined up. First, let me see if I can finish my Electronic Mural saga from January…
I decided I had to move, and thus redo, the control circuitry. This would allow two things: First, I could place the micro-controller next to the location of the power plug on the lilypad and run wire power leads directly to it, solving my power issue (which was that the resistance of the conductive paint was too high to transmit power for the microcontroller over a long distance). Second, I could connect the LED leads to different pins, somewhat ignoring my strange micro-controller pin problem by not using that pin.
I was sad to rip up the circuitry. I could have reused the stickers, I had some conductive double-sided tape, but they were pretty beat up after being pulled up and I had extras. I washed off the circuit scribe ink with water as well as the parts of the bare conductive paint that needed to be redone. I redid everything using the conductive paint, eager to retest the LEDs.
Bare conductive paint has a disturbingly higher resistance when wet. In moments of anguish I would use a heat gun over the paint to help it dry faster, but the best thing was to step away for an hour to come back to perfectly dry paint which would not be changing its resistance. The resistance would be lowest if I could paint it on as thinly as possible, but the stuff was thick and goopy — difficult to apply finely. I had not considered thinning it out with water, though in retrospect that might have aided things greatly. I couldn’t tell if the thickness was normal or because of age. I know that the paint will dry out completely, even in the bottle, if left for a long time (I once found an old bottle completely hardened) but I’m not sure if you can resurrect it.
One issue with using the bare conductive paint was that I couldn’t paint it thinly enough to connect the sound sensor without having to jump an electrical line. The circuit scribe ink went on slowly but finely and I could weave the sensor line underneath the circuit sticker. With the bare conductive paint this would be impossible.
I had planned to paint over all the conductive paint lines with white paint, allowing me to paint the mural as if the circuitry was not there. I had been told by kind folks all over the internet (not directly) that yes, you could paint over it easily with acrylic paint. So when redoing the control circuitry I thought I could make a clever bridge for the sound sensor by painting over the conductive paint with acrylic paint, allowing the sensor line to cross the power lines.
This is categorically not true. Lies! Let me write it in bold: You cannot paint over bare conductive paint with acrylic paint. No one has ever tried this, because as soon as you paint over the conductive paint with acrylic paint, they begin to mix. You drag conductive paint everywhere you want the acrylic paint, even if you’re extremely slow and careful. My bridge idea did not work in the least. Additionally, a large part of my concept for this mural was that the electronics could be hidden in the paint. I was distraught. I went to an art store, looking for guidance.
I went to two. In Central Square in Cambridge, MA there are two conveniently located across from each other.
In the first I talked with a confident lady in a well-used art apron who, while flummoxed by my explanation of the electronic mural, explained to me in great detail that no acrylic paint would work, (“But surely,” I would complain, “some acrylic paint is mostly plastic!”) because it was all water based. That’s why you can wash your brushes in water. I needed oil paint, she explained, though she wasn’t sure it would work well over this conductive paint nonsense I was working with. She found me some small jars of sign paint, (“It’s oil based,” she assured me, “and paints on almost anything.”) and told me I should wait until the sign paint dries completely before painting over it. This could be days, she said, breezily looking over the bottles for the correct time period. Just wait days, she said. I gulped. I had to finish the mural in the next two days, because I was leaving the country. I bought the small jars and some turpentine-equivalent (for washing my brushes) and headed across the street.
In the second I talked to a far less confident lady with many piercings who wasn’t sure that anything would work at all, and certainly not oil paints. Oil paints and water paints don’t work well together, she explained with graphic imagery of paint bubbling up through paint in a gross mess. Maybe, she said, you could try spray painting over the conductive paint. That way you don’t disturb it with the brush and cause it to mix. My jaw almost dropped to ground at her apprehensive genius. Yes, yes, I said. She started talking, still hesitantly, about some different spray paint brands and how she thought, maybe, one had less water, because once they had this brand whose selling point was more water and therefore… I bought two cans of white spray paint of the recommended brand and fled back to the mural.
I did not even try the oil paints. I have never used oil paints and this seemed like a bad time to experiment. I tried the spray paint on the paint that was originally going to connect the power supply to the circuit (before I moved the wire leads much closer to the circuitry) and it worked like a charm, not disturbing the conductive paint underneath in the least. It was a great idea and I highly recommend it. The conductive paint showed through a bit underneath, not so much from color but from the raised contour and a slightly different surface texture. I thought this was a fine compromise. I felt so close to finishing.
Testing the spray paint over the conductive paint, and then using regular acrylic paint on top of the spray paint. Works great!