View source for Stop at given length from the wall

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=== Introduction === <!--T:1-->

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Often it is important to stop the robot if it sees an obstacle. The ultrasonic (or infrared) sensor is a suitable tool for that.

=== Robot === <!--T:3-->

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Any robot (with tires or treads, perhaps walking robots too) will work.

=== Sensors === <!--T:5-->

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The ultrasonic (distance) sensor is used. The sensor is attached to port number 4.

=== Example Videos === <!--T:7-->

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<youtube>r8FcMB5bwhA</youtube>

=== Theory === <!--T:9-->

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The ultrasonic sensor is a sonar radar that works similar to that of the bats. You should check the performance of the sensor in advance, specially if it is not working properly. A hand might be a not optimal device for checking -- you should use something more solid, eg. plastic of cardboard. The maximum working distance is about 2 meters, and the smallest distance is about 10 cm.

=== Example Code === <!--T:11-->

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[[File:Stop10cm.png|thumb|The code that stops the robot when in a proximity of a wall.]]

=== Exercises === <!--T:13-->

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* Make the robot speed dependent on the distance to the wall, e.g. by using a formula speed = distance.
* Use the ideas shown in previous part (Following a Line) to follow the wall at 10 cm apart.
* Follow a line (previous part) until the robot finds a wall at 10 cm apart from the wall.
* If you have multiple robots, make the robots follow a line and each others, not colliding with the robot in front of.
* Use the ultrasonic sensor to listen if there is other robots using ultrasonic sensors. 

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[[File:Ultrasonic.png|| Listen]]


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This course is supported by [https://meet-and-code.org/ Meet and Code]. The course is made in collaboration with [http://www.fllsuomi.org/ Robotiikka- ja tiedekasvatus ry].
[[File:MeetAndcodeLogo.png|thumb]]

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[[Meet_and_Code_2020_I:_Ev3-G | Back to Meet and Code 2020 I: Ev3-G]]

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