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(J) Using the Internal and Motor Sensors

In addition to the external sensors that attach to the sensor ports on the NXT (ports 1-4), the NXT brick itself also has some built-in sensors, and the NXT motors also have built-in Rotation Sensors that communicate to the NXT through ports A-C.

Using the NXT Buttons

The three buttons on the face of the NXT Brick (Left Arrow, Right Arrow, Orange Enter button) are accessible as sensors from a program and act almost exactly like Touch Sensors.  See the Single Touch Sensor section for ideas on basic use of these sensors.  One important difference between the NXT Buttons and Touch Sensors, however, is that the NXT cannot detect multiple NXT buttons being pressed at the same time, so strategies involving simultaneous presses, such as those used in the double-touch sensor remote controls, will not work with NXT buttons.  Also note that the fourth NXT button (dark gray Back/Abort button) is not accessible from NXT-G programs, as pressing this button will always abort the program. 

(Downloadable programs are available only on the CD "LEGO MINDSTORMS NXT 2.0 by Example").

Program Description and Observations Attachments
J1-AskNumbers   Expert
This program uses the AskNumber My Block, which shows an advanced use of the NXT Buttons to allow the user to enter a number into a running program using the NXT Buttons and the display.

The J1-AskNumbers program uses the AskNumber My Block twice to allow the user to enter a number of degrees and a power level, then uses the results to configure a Move block to make the robot drive the specified distance at the specified power level.

The AskNumber My Block is complex internally, but using it in a program is simple.  You simply specify the name for the value to be displayed on the screen, and the minimum, maximum, increment step, and default (start) values in the block's configuration panel, and then the block handles all of the user interaction and display and outputs the final number chosen from the Number Out data port.

(none required)

 

Using a Timer

The NXT-G programming system provides a few simple ways to do timing that are built into other blocks, such as the Wait block with Control set to Time, the Move block with Duration set to Seconds, and the duration of Sound Tone.   However, these controls do not allow you to keep track of time while other blocks in the program are running.  To measure time without pausing the program, you can use the Timer block.

(Downloadable programs are available only on the CD "LEGO MINDSTORMS NXT 2.0 by Example").

Program Description and Observations Attachments
J2-ReactionTest   Advanced
This program uses the Timer block to play a little reaction test game on the NXT.  The program will display "Ready..." then wait a random of time (using the Random block), then display "GO!" and time how long it takes for the user to press touch sensor 1.  You can use the Touch Sensors remote or just a loose touch sensor on a wire to the NXT. 

Since the program does not know how long to wait (and is in fact waiting for a sensor press), it must time the action with the Timer block.

Touch Sensors
(as Wired Remote)

 

Using the Rotation Sensors

The NXT motors each have a built-in Rotation Sensor that can measure the rotation or angle change in a motor accurate to 1 degree and keep track of the total degrees turned since the program started or the last time the sensor was Reset.   In addition to the simple uses of the Rotation Sensors built into the Motor and Move blocks (see the Driving Straight and Turning sections), you can also measure rotations independently in a program using the Rotation Sensor block.

(Downloadable programs are available only on the CD "LEGO MINDSTORMS NXT 2.0 by Example").

Program Description and Observations Attachments
J3-DispMotors   Intermediate
This program uses the DisplayMotors My Block to simply display the rotation angle of all three motors while the motors are idle (not being powered).  Run the program, then turn Multi-Bots wheels/treads and/or arm by hand and watch the degrees displayed on the screen.  Press the Enter button on the NXT at any time to reset (zero) all three rotation sensors.

Motors do not have to be powered to measure their rotation.  You can turn the motors by hand or any other action, and the rotation sensors will measure the amount of their rotation.  This can be useful or making things like a hand-turned dial, using an unpowered motor. 

Golfing Arm
(Optional)
J4-PathRemote   Expert
This program uses the DisplayMotors My Block and the Touch Sensors remote control to make a remote-controlled path measuring robot.  You control the robot with the remote control, and the program will display the number of degrees travelled by each motor.  You can zero the sensors at any time and also adjust the motors by hand at the end of a motion.  This can be used to measure the Duration (in Degrees) needed by a sequence of Move and Motor blocks to get the robot to travel along a desired path by itself.

Control the robot as follows:

  • Enter the Power (speed) to use at the beginning of the program using the NXT buttons.  Slower speeds will generally be easier to control.

  • Press and hold both touch sensors to drive straight forward.

  • Press and hold the left touch sensor (1) to do a
    one-wheeled left turn.

  • Press and hold the right touch sensor (2) to do a one-wheeled right turn.

  • Release both buttons to stop.

  • After stopping a motion, you can adjust the desired robot position by turning the wheels by hand if desired.

  • Press the Enter button on the NXT at any time to reset (zero) all of the sensors.  Typically you will want to reset after each type of motion, to measure for a sequence of Move and Motor blocks.

Touch Sensors
(as Wired Remote)

 

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