Icon of block

Acceleration Sensor Block

This block measures the three axes of acceleration, x, y and z. It returns the readings as signed values ranging from -400 to +400 thus the scale factor is approximately 200 counts per g, so the sensor can measure +/- 2g. Using data wires, it can send out the x, y and z values and a logic signal (true/false) based on whether the x value is above or below a trigger value.

A trigger value is a value against which the reading is compared to produce an output condition. For example, you might program your robot to react if it is tipped up, so you might set the trigger value to 70. When the reading from the sensor exceeds 70, ie; the robot is tilted up more than 45 degrees, the condition will be true.

Specify the trigger value by using the slider or by typing the value into the input box. 

The default setting for the acceleration sensor block is for the trigger to be set to 0 to produce a "true" signal. 

You must drag at least one output data wire from this block's data hub to another block for any information to be sent.

Display Settings

  1. The number shows which of your NXT's ports are connected to the acceleration sensor. You can change this number in the configuration panel if you need to.
  2. The block's data hub will open automatically when the block is placed in the work area. At least one data wire must be dragged from the block's output plug to another block's data hub. The trigger value and other features can be set dynamically by connecting an input data wire. (See the Data Hub section below for more information.)

Configuring the Acceleration Sensor Block

Image of configuration panel

When configuring the sensor to be connected via the multiplexer, there are two port selections to make. The first is the NXT to MUX connection port and then the MUX to SENSOR connection port.

To configure the NXT to MUX connection, select the NXT port that is connected to the MUX using the port selection as shown below.

To the right of the port selection is a right arrow symbol . Click on the arrow to display the next port selection group.

When this is displayed, select the MUX port the sensor is connected to.

  1. Choose the port where your compass sensor is plugged in. By default, the block will be set to port 3 for an acceleration sensor. You can change this selection if you need to.
  2. If you choose the Compare function, the block will be triggered when the x axis reading  is above or below the selected value; select < "less than" to trigger the block when the reading is below the trigger value or > "greater than" to trigger the block when the reading is above the trigger value. Use the slider to set the trigger value or type it directly into the input box. 

Note: The acceleration sensor can only compare the x reading with the trigger value. If the direction in which you wish to perform the comparison on is not the x axis of the sensor, you can either remount the sensor to make the x axis the one you are trying to detect or you can wire the sensor block to a Compare block to do the comparison of the desired axis. 

Configuring the Acceleration Sensor block's Data Hub

You can control the Acceleration Sensor block dynamically by connecting data wires (from other block's data hubs) to the Acceleration Sensor block's data hub.

Open a block's data hub by clicking the tab at the lower left edge of the block after it has been placed on the work area.

Image showing unopened tab on a generic block

Data wires carrying input information to a block are connected to the plugs on the left side of its data hub. Data wires carrying output information are connected to the plugs on the right side.

Image of data wires

[A] Input plug
[B] Output plug
[C] Number data wire (yellow)
[D] Logic data wire (green)
[E] Text data wire (orange)
[F] Broken data wire (gray)

Passing data from the input plug to the output plug

If an input plug has a corresponding output plug (see A above), the input data will pass through from the input plug to the output plug without being changed. In this case, you can only use the output plug if the input plug is connected to an input data wire; connecting an output data wire to such an output plug without a connected input data wire will cause the output data wire to be "broken" (and colored gray).

Data wires carry specific types of data

Each data wire carries a specific type of data between blocks. For example, if a data wire is dragged from a logic plug on a block's data hub, it can only be connected to a logic plug on another block's data hub. The chart below shows what kind of data each plug can accept or send out.

Data wire colors

Data wires are identified with specific colors: wires carrying number data are colored yellow, wires carrying logic data are colored green, and wires carrying text data are colored orange.

"Broken" data wires

If you try to connect a data wire to a plug of the wrong data type, the data wire will be broken (and colored gray). You will not be able to download your program if a data wire is broken.

If you click a broken wire you can read why it is broken in the small help window in the lower right corner of the work area.

Data must be within the possible range of the plug

If an input data wire transmits a value outside the possible range of the plug it is connected to, the block will either ignore the value or change it to a value within its range. For plugs that allow just a few input values (example: just 0, 1, or 2), the plug will ignore the input if a value arrives outside its range.

For plugs that accept larger input ranges (example: 0 - 100), the plug will force any input outside its range to fit. For example, if a Move block's Power plug receives an input value of 150, the block will change the input value to 100 (i.e., a number within the Power plug's range).

Acceleration Sensor block Data Hub plugs

You must click on the Data Hub to open it as shown.

Image of block

 













  1. This plug wires the number for which of your NXT's ports are connected to the Acceleration sensor. 

  2. This plug outputs the x value.
  3. This plug outputs the y value.
  4. This plug outputs the z value.
  5. This plug outputs the Above/Below logical value.
  6. This plug wires the threshold value.
  7. This plug wires the greater than/less than control.

 

Understanding the x, y and z axes

Image of configuration panelThe Accelerometer Block has three outputs, x, y and z which are derived from three measurement axes. These axes are set in the three principal perpendicular directions as defined by the sensor housing.

The x axis is the principal axis which can be compared against the threshold as well as being available as an output value. It represents measurements of acceleration along the body of the sensor as shown in the picture. This axis may also be used to measure the forward/backward tilt assuming the sensor is mounted "level" on the robot. Forward/backward tilt is sometimes referred to as "pitch".

The y axis is only available as an output value. It represents measurements of side to side acceleration as shown in the picture. This axis may also be used to measure the side to side tilt assuming the sensor is mounted "level" on the robot. Side to side tilt is sometimes referred to as "roll".

The z axis is only available as an output value. It represents measurements of up and down acceleration as shown in the picture. This axis will be measuring the downward force of gravity if the sensor is mounted "level" on the robot.