It is also possivle to combe copper tape and saltwater to create functioning circuit paths. I tested out this method by building a circuit board that has an photoresistor integrated. Thus the buil paper device can react towards light changing within it’s environment. The LED again serves as an examplary, triggered reaction when a reduction of light is detected. Here a sketch taken from http://arduino.sundh.com how the circuit would look like if you use primarily metal-based materials like a breadboard and jump wires.
Instead of using a breadboard and jumping wires, copper tape can be stuck to the paper’s surface to connect the arduino board’s connection pins and all needed elements for the circuit. As the copper tape has one sticky side, the resistor, LED and photoresistor can be fixed onto the copper-based paths. Also the connection tends to disturbed sometimes, as the folded copper material tends to change it’s position and therefore loses a touching point with the electronics pin.
Never the less – the connection between the A0 pin and the photoresitor pin is not established by a stripe of copper tape. Once the paper in between gets wet with saltwater, the whole circuit is closed and working.
Of course the whole circuits can be realized without any copper tape by simply using Cirquids. But you might consider one thing I learned during realizing this circuit board: Due to resistence loss caused by the paper’s properties, it might be necessary to attache the integrated electronics to each other to provide enought current flow (as only 5V were attached to the circuits).
Here is a picture of the unsuccessful, first version. As you can see the LED is barely lightning up.
Here is the improved version, finally the circuit works with applying only 5 volt.