NXT IRSeeker

HiTechnic NXT IRSeeker Sensor
For LEGOÒ MindstormsÒ NXT

 

Introduction

The NXT IRSeeker is a multi-element infrared detector that detects infrared signals from sources such as the soccer ball used in RoboCup Jr competitions.

 

 To test for the IRSeeker, plug it into port 1 of your NXT brick and select View – Ultrasonic cm – Port 1. As you rotate the sensor from right to left in front of the infrared source, you’ll notice that the readings will change from 1 – 9. If there is no infrared source within range, the value returned is 0 which will display as ?????? in Ultrasonic mode. This is a display of the direction only.   Note that if you are near a sunny window, you will detect the infrared in sunlight which may interfere with the detection of other infrared signals. 

 

The IRSeeker direction values are shown here with 1 indicating the infrared target is left and behind, 5 if the target is directly ahead and 9 if the target is to the right and behind.  A value of 0 is returned if no signal is detected.

In addition to direction, the IRSeeker also returns the relative signal strength of the infrared signal detected by each of the five detecting elements so an estimate of distance to the target can be made. 

 

 

 

 

Programming

Mindstorms NXT-G

The compass can be programmed using LEGO Mindstorms NXT Software IRSeeker Block.  If the IRSeeker Block is not available you may also use the standard Ultrasonic Block.

 

Ultrasonic Block

If using the Ultrasonic Block to read the IRSeeker, configure the block to centimeter mode as shown.

 

The Ultrasonic Block will return values from 1 to 9 indicating the direction to the target as shown above and a value of 0 if no infrared target is within range.

IRSeeker Sensor Block

The IRSeeker Block returns the direction and relative strength from each element.

 

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

2. This plug outputs the direction value.
3. This plug outputs the source detected logical value.
4. This plug outputs the Channel 1 signal strength value.
5. This plug outputs the Channel 2 signal strength value.
6. This plug outputs the Channel 3 signal strength value.
7. This plug outputs the Channel 4 signal strength value.
8. This plug outputs the Channel 5 signal strength value.

 

Sensor Register Layout

 

If programming the IRSeeker using NXC or RobotC programming languages, the register layout table gives the  

Address	Type	Contents
00 – 07H	chars	Sensor version number
08 – 0FH	chars	Manufacturer
10 – 17H	chars	Sensor type
42H	byte	Direction  ( 0 - 9 )
43H	byte	Sensor 1 signal strength
44H	byte	Sensor 2 signal strength
45H	byte	Sensor 3 signal strength
46H	byte	Sensor 4 signal strength
47FH	byte	Sensor 5 signal strength

 

The Sensor version number field will report a revision number in the format “²Vn.m” where n is the major version number and m is the revision level. Revision numbers will typically reflect the firmware level. The version number will be used to indicate the hardware level.

The Manufacturer field will contain “HiTechnc”.

The Sensor type field will contain “IRSeeker”.

The Direction field will return the currently measured direction of the infrared signal as a value from 0 - 9.

The Sensor signal strength fields will return the relative strength of the infrared signal deteceted by each of the five detection elements.  The values returned will be depend on the strength and distance of the target signal.

 

 

Other Programming Environments

RobotC

All features of the HiTechnic IRSeeker can be accessed using RobotC.  For more information go to http://www-education.rec.ri.cmu.edu/robotc/.  

 

NXC

NXC is a comprehensive C programming environment that can access all IRSeeker features.  For more information go to http://bricxcc.sourceforge.net/nbc/.

 

Notes:

• NXT Firmware version 1.03 must be loaded in the NXT for the IRSeeker to operate correctly.  You can check the firmware version by  displaying the NXT Window in the Mindstorms software.
• If the IRSeeker is being used to detect relatively weak infrared signals such as those from a RoboCup Jr soccer ball, don't get too close to windows with sunshine streaming in as the infrared from the sun will be much stronger than from the soccer ball.

 

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