To build a simple sensor to detect rainfall and to brainstorm ways a sensor can activate simple devices.
One class period
National Education Standards
Materials: (Per Group)
Transfer of energy
Students will develop an understanding of and be able to select and use information and communication technologies.
Communication systems are made up of a source, encoder, transmitter, receiver, decoder and destination.
- Six-volt lantern battery
- Wire (Wires with alligator clips are recommended.)
- Six-volt light bulb and socket
- Small piece of wood [about 4 inches (in) by 4 in, or 10 centimeters (cm) by 10 cm]
- Heavy duty aluminum foil
- Spray bottle filled with water
- Student Page
- This lesson can be used as a demonstration, an exploration activity for a science project or an introductory activity for a unit on circuits and electricity.
- Build a simple circuit (like the one pictured below) to demonstrate how closed and open circuits behave.
- Adding salt to the water will help conductivity (useful for younger grades), which will help ensure success of sensor circuit.
Sensors are usually designed to monitor one thing at a time. If more than one condition needs to be monitored, more than one sensor is used. Sensors can measure light, temperature and other things. Simple sensors will basically answer a yes or no question [Is the temperature above 90 degrees Celsius (194 degrees Fahrenheit)?]. The computer monitoring the sensor will decide how to use this information.
- Discuss the importance of sensors. Bring up the idea that sensors can be placed where it would be impossible or impractical for a human to observe environmental changes.
Image to right: This shows a simple circuit with a switch. Credit: NASA
- Demonstrate the simple circuit to the class. Encourage them to observe what happens when the circuit is turned on, creating a closed circuit. What happens when the circuit is turned off, creating an open circuit?
- Tell the students they will use a simple circuit as a guide to build a sensor to detect rain.
- The simple detector they will use will be two strips of metal with a very narrow gap between them. When raindrops fall on and bridge the gap, they will complete (close) the circuit, turning on the light.
Image to right: This shows a simple circuit with a sensor. Credit: NASA
- Discuss procedure and safety instructions with students.
- To test the circuits, spray them with a spray bottle. (BE CAREFUL TO ONLY SPRAY THE SENSOR!)
- If the wood is absorbing the water, slip a thin piece of plastic underneath the metal strips.
- To make sure the connections on the circuit are working correctly, use a paper clip to bridge the gap between the pieces of foil. This should close the circuit and cause the light to glow.
- After cleanup, discuss the activity/demonstration.
- Brainstorm ideas of where this simple sensor could be useful. What could you replace the light with to make it more useful? (One idea is to replace the light with a motor to close a sunroof if it starts to rain.) Be creative.
- What other things might close the gap, causing the sensor to turn on when no rain is present?
- Examine a more complex sensor (where the detector is more complex) such as one contained in a fire alarm. (Different types are designed to detect different events.)
Rain Sensor Student Page
- Display a variety of other electronic materials for students to explore and from which to build other sensors. (A burglar alarm with a pressure-sensitive "switch" and a buzzer attached to a doorway would be fairly simple.)
- Set up a real classroom sensor that can be placed outside to monitor the weather.
- Determine which student group built the most sensitive sensor. Why could a sensor that is too sensitive not be useful?
- Have students draw their designs and research their inventions on the Internet to see if they already exist.