After visiting The Hacktory’s “Soft Circuit” event, PJ and I were inspired to take a stab at making some micro-controller circuits using alternative, “high/low tech” approaches. PJ made an MCU circuit using conductive paint (has potential, but needs some tweaks). I opted to try a circuit board using metal leaf. That happened to work on the first shot — although careful scrutiny of the picture on the left suggests there was some luck involved (there are holes in the circuit that come dangerously close to wrecking it).
I had considered using scored foil as a way to make free-hand, one-off circuit boards for quite some time — but until recently, I never had the mix of free time and raw nerve to actually try it. It turns out that my reservations were probably well-founded, but it also happens that the technique is workable, and the results are actually aesthetically interesting.
We decided to make the board in a hexagonal shape (Hive76 — hexagon — get it?). First, we prepped circuit board material by spraying adhesive on card-stock and then sticking the faux gold-leaf on the prepared surface (this sounds simple, but the foil is maddening stuff, so the process involved profanity and a certain amount of despair). Then we cut the foiled card-stock into hexagons. After that, we cut out a rectangle where the IC was going to go, so that there were no conductive paths under the chip. Once the board was roughly prepped, we made a “squashed bug” of the IC , splayed its pins out, and soldered it to the gilded surface. Using the gaps between the pins as a guide for an exacto knife, we cut free-hand traces that routed the pins of the chip to large zones on the edge of the hexagon (I was a little surprised that the cuts were free of bridges). Finally, we soldered a capacitor between the MCU’s Vcc and ground and soldered a 47k resistor between Vcc and the MCU’s reset line. At that point, we had a working circuit that was in-system programmable — at least in theory.
Unfortunately, I had no idea how we might program the MCU or hook it up to external circuitry without damaging the fragile structure. PJ came up with the idea that made it all workable … magnets. All really good magic is done with magnets. The idea here was to place the paper computer on a steel surface, which allowed us to stick magnets wherever we wanted to make a connection. With steel under the circuit, the down-force of the magnets gave us firm-but-gentle electrical contact with the delicate foil. Once the magnets were in place, we only needed to touch alligator clips to them — since the clips were steel, they stuck happily. With the clips secured to selected points on the MCU, we were free to connect the opposite ends of the clips to the various external items needed for the circuit. Note the ingenious use of paper-clips. PJ again — see a pattern here?
Our first connection was power (two magnet connections, one for +3.6 volts, the other for ground). Then we hooked up the Spy-bi-wire programming interface (two wires, two more magnets). After that, we wrote the obligatory “blink LED” program and loaded it into the paper computer. Naturally, we wanted to see the results — two more connections for the LED terminals and — Voila! Here’s the movie …