Engineers Month Activities, 2008
In cooperation with the IEEE Oregon Section, The Oregon IEEE Consultants' Network , and the Business Education Compact Circuitsville Engineering was a presenter to a fifth grade class at Cooper Mountain school in Beaverton Oregon in February 2008. All of this required working with the teacher to intergrate my presentation into things the class was studying.
The presentation consisted of two parts.
The first part was a quick discussion of how electricity is understood, using the analogy of water: the measurement called "Voltage" is similar to water pressure and the electrical property called "Current" is similar to water flow. The second connection comes from the British explanation of vacuum tubes as 'valves', objects that could be turned on or off electrically but control the flow of electricity, just like a faucet valve controls the flow of water. This led to the first demonstration circuit, using a screwdriver to turn on the 'valve', in this case a MOS FET transistor.
The variable resistor or potentiometer allows a variable DC voltage to be applied to the Gate of the FET. Once the applied voltage is above the Threshold Voltage of the FET it begins to conduct. This allows current to flow through the LED and, if selected, the buzzer. At the top end of the pot the LED and buzzer are fully on, both brightest and loudest. The circuit was powered off of a 4.5V "wall wart" AC to DC power supply.
The second part of the presentation fit into the teachers classroom activites of student designed innovations and inventions. In this particular case, one student had designed a pencil dispenser. The Circuitsville Engineering designed a simple, battery powered circuit that indicated when the dispenser was empty.
There are two ways to accomplish this. The first is to use a microswitch (S3 on the right edge of the drawing) to sense when the pencils are gone. The second method would require adding a 'fin' to the bottom of the plate that forced the pencils up. This fin would interrupt the light beam in the photo interrupter when the dispenser was full, but when empty the fin would be pushed out of the light beam and thus would turn on the LED. The circuit for this is shown at the bottom of the drawing.
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