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WeDo sensors

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Lego WeDo motion (top) and tilt (bottom) sensors.

Unlike its big siblings the NXT and the EV3 (see NXT sensors), the WeDo kit only has two sensors. Nevertheless, these sensors give students the opportunity to experience how robots sense the world around them.

Note: The NXT/EV3 sensors cannot be used with the WeDo kit.

Motion sensor

The motion sensor (part 9583) can detect objects very roughly up to 15 cm away, depending on the shape of the object and other properties (reflection, colour, etc.). It is sometimes called a distance sensor.

Very technical details: The motion sensor is an active IR (infrared) sensor. One of the visible parts emits a light while the other is the detector. The LED light is pulsed at 7 kHz. You might be able to see (and show) the flashing light using a camera phone. The sensor can work with 5 to 9 volts, with the WeDo set at 5 volts.

Tilt sensor

The tilt sensor (part 9584) detects changes in position. It can detect six different positions: tilt this way, tilt that way, tilt up, tilt down, no tilt and any tilt. On occasion, the vibration of the motor will interfere with the accuracy of the tilt sensor. The fix for this is to design a construction in which the motor vibrations are isolated from the sensor.

Using the computer’s microphone

Even though the WeDo does not have a sound sensor, it does make use of the built-in mic on the computer. The WeDo can be programmed to display how loud a sound is or to start the motor when a sound is sensed.

Introducing the sensors to young students

Older students will have no problem understanding how these sensors work. For younger children, the teacher might want to link them to the senses we have as people (or animals). Ask students to name the senses. Most students will name five (sight, hearing, taste, smell, and touch) but in this case, it is useful to include the sense of balance. Then, help students see that sense and sensor are very similar words. From there, the motion sensor can be linked to sight and the tilt sensor to balance (and the computer mic to hearing). Many students will be familiar with the beeping sound when a car is backing up or when the light turns on automatically when they enter a room or approach the front door. Recalling these experiences will also help students understand the motion sensor.

WeDo sensors and Scratch

One interesting ability of WeDo is that it can integrate with the programming language Scratch. When this is done, input from the sensors can be used with Scratch. For example, a Scratch program could be set to wait for a change in tilt and when it happens, it could display on the computer, “Watch out, you are going downhill.” A plugged-in WeDo creation with a tilt sensor would cause this message to be displayed if moved in the required direction. More information can be found here. In Scratch, the motion sensor provides a rough indication of distance where 0 (zero) is close and 100 is far. Similarly, the tilt sensor can report orientation where 0 is flat, 1 is down, 2 is right, and 4 is left. Activities incorporating Scratch would be more appropriate for older students, at least upper primary.

Note that the sensors must be attached to the LEGO USB hub (which in turn must be attached to a computer). When they are attached, the computer automatically detects their presence and can use the input. Using the WeDo software, up to three hubs can be attached to a computer, allowing for more motors and sensors. When using Scratch, only one hub can be attached.

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Wayne Burnett

Wayne Burnett

Wayne Burnett, Ed.D., is a Canadian father of two boys (both of whom used the Mindstorms NXT) who teaches at an international school in Singapore. In addition to teaching robotics, ICT, and information literacy, Wayne has recently completed a dissertation on using the LEGO WeDo to teach science.

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