Solar Cell Photon Toss Exhibit
| K-12 Outreach Kits and Labs |
Overview
The Solar Cell Photon Toss is a desktop or freestanding interactive exhibit that is good for younger audiences or families. The poster graphic is mounted on a rigid board with a hole at the center at the junction layer. Behind the hole is a hinged panel and a microswitch which connects to strips of LED lights which flash when the circuit is completed. The switch is adjusted so that it requires the force of the heavy blue bag in order to actuate.
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Science topics to discuss
Conversation Starters Can you make electricity with sunlight? These bean bags represent sunlight of different colors. Throw them at the solar cell and see what happens.
Here are some of the topics that can discussed with kids and parents as they toss the bean bags.
- Sun light is made of many colors
- Blue light has more energy than red light
- Much of the solar radiation is invisible Infrared which can pass through clouds
- We need to develop solar cells that generate electricity using the whole spectrum
- Solar cells can be made of layers of semiconducting plastics
- A photon must absorbed near the junction between the acceptor and donor layers for a current to be generated
- After a photon is absorbed an electron moves one direction and a hole moves the other direction forming a complete circuit.
Construction
The poster is printed glued to a 1/2" plywood backboard. An 8" hole is cut in the center. Behind this 4" deep box is mounted containing a hinged board. The board is supported by a spring so that tension can be adjusted with a threaded bolt. The microswitch connects to the power supply and then to an LED light strip and a oscillating color LED. The lights sit behind the poster in a groove that is routed in the backboard. Another hole at the bottom allows bean bags that get through the hole to pass be retrieved.
There are three types colors of satin bean bags, red is filled with light fiberfill, green is filled with half fiber and half beans, the blue bag is filled with beans. The tension on the spring is adjusted so that blue bag trips the switch and the green only trips it when it is thrown really hard.
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We used an Arduino UNO as a programmable timer so we could turn the circuit on and off every second for 5 seconds by way of a relay. Download Arduino blinking LED sketch
Another approach is install a series of LEDs along the path of the wire every 2 inches and then switch these in sequence using the Arduino and a 74154 multiplexor. The multiplexor takes 4 outputs from pins 10,11,12,13 of Arduino input into its pins 20,21,22,and 23 which turns off multiplexor pins 0 to 15 in sequence.