By McKenna Cisler
WMSI recently began developing a new kit for use in paper circuits—circuits built out of copper tape on cardboard. The kit—dubbed the “Spider” for its bug-like appearance—is intended to add new and interesting functionality to basic paper circuits. With the Spider, kids can go from simple circuits of series and parallel LEDs to exciting projects with blinking LEDs controlled by how hard they push down their finger. The Spider’s central microcontroller and its reprogrammability provide even more opportunities: everything from paper speakers and electromagnets to the concepts of digital signals.
The Spider’s brain - an ATtiny85 microcontroller
The Spiders’ design is centered around the ATtiny85 microcontroller, a “tiny” device equipped with nearly all the functions of an Arduino. The ATtiny has 5 “pins” which can be programmed to either sense a voltage or output one. For example, it can read a voltage on one pin to see whether a button has been pressed, and then output a voltage on another pin to light up an LED if so. It is essentially the simplest (and smallest) form of a modern computer--it takes input from a user and does something else based on that input.
A circuit of blinking LEDs with the Spider’s ATtiny85 out of its socket to be reprogrammed
The Spider’s ATtiny can be taken out of its socket and put in a Tiny AVR Programmer, where it can be reprogrammed using Arduino software to do any number of things with a paper circuit. Our first couple programs were designed to make interesting patterns with LEDs: we made them twinkle, come on randomly, and flash in a series. After figuring out how to change the outputs, we started to use input to change what the ATtiny did, setting up a button that would change the direction of the blinking LEDs when pressed.
Controlling the LED blink rate with finger pressure
Then, using the ATtiny’s analog input pins--capable of precisely measuring voltage--we controlled the blinking speed by changing the resistance between two contacts. A lower resistance means electricity can flow more easily, so the ATtiny would read that less voltage is required for it to bridge the gap. This unleashed all kinds of possibilities when paired with a paper circuit: now kids can explore how the resistance of everyday things, such as pencil lead or salt water, affects the blinking of LEDs in their very own paper circuit.
A fully-featured paper audio circuit, complete with plenty of batteries, a pencil resistor, paper speaker, and paper buttons.
However, the coolest function was yet to come. Inspired by our past work with paper speakers, we designed a new Spider with an onboard transistor for feeding more power to our speaker. We then programmed the ATtiny to play some simple sound effects from the era of 8-bit video game music. From there, we delved into the mechanics of audio to program the Spider to play certain melodies (naturally starting out with the Imperial March). The result was a loud but exciting noisemaker--made of just paper, copper tape, a magnet, and a Spider!
A prototype LED Spider hot off the manufacturing line
Putting microcontrollers into paper circuits has unleashed all kinds of possibilities with copper tape and cardboard, and we’re excited to see where students will take it! And with our open source code, anyone can explore our Spider programs and write exciting new ones. We’ll even be selling a “programmer's kit” with everything budding Spider developers would need. Keep an eye out for Spiders coming soon!