Servo - October 2010

www.servomagazine.com/index.php?/magazine/article/october2010_Intermaggio

We’ll start by getting a broader understanding of the light sensor and its functions.

• What exactly does a light sensor sense?

• What are some practical applications for a light sensor in consumer electronics?

• How can we use the light sensor within the NXT system to learn more about robotics?

After answering these questions, we’ll build two light sensor attachments for our robot: one using just one light sensor, and a second with two light sensors.

If you only have one light sensor, have no fear! We’ll be focusing on the single light sensor attachment, offering the double light sensor attachment as a challenge! Next time, we’ll be covering multiple sensor programs, so you may want to purchase an extra light sensor from LEGO Education ( http://bit.ly/lightsensor).

What exactly does a light sensor sense?

A light sensor uses a photovoltaic cell to detect the intensity of the light it is exposed to. It can sense either reflected light (light originating from the sensor itself and reflected off the nearest surface) or ambient light which is light naturally existing in the robot’s environment. To put it simply, a light sensor will sense the intensity of light that it is exposed to, whether by itself or its environment.

What are some practical applications for a light sensor in consumer electronics?

Probably the most common use of photovoltaic (light sensitive) cells in consumer electronics are street lamps that turn on automatically at night. If you’ve ever been down a road at dusk and watched different streetlamps turn on and off at different times, it’s more than likely small variations and imperfections in the photocells are causing them to turn the lights on at a different threshold.

Beyond that, light sensors have many more interesting applications. Lots of cellphones are now equipped with light sensors to save battery life — screens need to be brighter during the day to be visible, but at night it’s not necessary, so screens dim automatically to save power.

How can we use the light sensor within the NXT system to learn more about robotics?

We could certainly make a LEGO street lamp or a LEGO automatic dimmer switch, but that would be boring! We’ll be taking a much more hands-on approach to learning about the light sensor by creating several programs that move and react based on the readings received.