Grades K–2 · Computing
How can a light beam help a door respond?
A door can begin opening without a hand touching it. In the light-beam arrangement shown, a source sends light toward a receiver on the other side.
In the diagramA door can respond to a change in lightA toy through-beam sensing systemSourceReceiverDoorControllerbeam interrupted; door open.The sensor notices a light change, not an identity.
The person blocks the beam, so less light reaches the receiver. The receiver is a sensor: it turns a change it notices into a signal. A controller responds by switching on a motor, which moves the door open. The light carries the clue; the powered motor does the moving.
An opaque box would block the beam too. The signal means that the light changed, not that the sensor knows who arrived. Real doors can use other kinds of sensors.
About this explanation
Starting knowledge: Learners need everyday ideas of light being blocked and a door being open or closed; adult read-aloud is suitable.
Sources
- OMRON Industrial Automation — Overview of Photoelectric Sensors