When we at The Hacktory were invited to present a hands-on activity for The Davidson Young Scholars’ gathering at the Academy of Natural Sciences, one scientific exercise came immediately to mind:
Students of all ages used conductive play dough and electronic components to sculpt a fantastic menagerie of glowing, moving clay creatures. As they exercised their creativity, the students also got to explore the science behind circuits and electricity (a principle which happens to be part of The Hacktory’s core educational values!)
To assemble our squishy circuits dough, we used instructions from the University of St. Thomas. They recommend a salt-flour-water ratio 1:4:4, with vegetable oil and cream of tartar added for texture and stability. The mixture is cooked on a stove, cooled, and then more flour is kneaded in by hand until the desired consistency is reached.
The first batch we produced wasn’t conductive enough. Its resistance measured over 100 kilohms, which made it impossible to light an LED with the 3V we expected they would need. Via Ohm’s Law: I = V/R, so with 3V and R=100,000, our LEDs were only getting .03 milliamps, and they would need closer to 10 mA to produce any light.
We theorized the initial batch had been too moist when we removed it from the stove, and in order to get it less sticky, we had worked in too much extra flour, lowering its conductivity. Back to the kitchen we went! We made another batch, cooking it until the mixture was drier and less sticky to touch. This was much more successful, with resistance measuring around 2 kilohms. We also switched to larger 12V battery packs, allowing our LEDs to draw around 6 milliamps. With LEDs aglow, we declared victory and made several batches of fun colors.
We also made a batch with triple the salt, under the theory that this would be still more conductive. To our surprise, it was not, and the grainy texture of this extra-salty dough was characterized by the students as “gross.” The next time we make a batch, we’ll try adding more cream of tartar (KC4H5O6) — perhaps more potassium ions will increase conductivity?
In addition to 12V 8x AA battery packs, we also had success with single 9V batteries, and a 6V 2x CR2032 cell holder from Adafruit. The most popular parts were the chunky 10mm diffused LEDs, like this model. We also brought an assortment of electric motors we had recycled from old toys.
Other lessons learned:
- Alligator clips are hard on little fingers. (They’re hard on our adult fingers, too!)
- Multimeter probes get gunked up with dough pretty quickly and require cleaning for accurate measurements.
- Applying 12 volts directly to a standard LED with no conductive dough in between as a resistor WILL render the LED unusable (and make a bad smell as you let the magic smoke out.)
- Sharing is good, but each participant having his/her own battery pack is better.
- The female equivalent of a “Brony” is known as a “Pegasister.”
If squishy circuits sounds like fun to you, be sure to check out the other cool classes we have coming up at The Hacktory!