Seeing the light - IR Beacon and Seeker basics

Editor's Note: This post was originally published in the Ring It Up! season and has been updated to reflect the introduction of the 360 degree IR Beacon introduced by HiTechnic in the 2013-14 season.

By Tom Eng

FTC Engineer

Update on the IR Beacons (1-28-14)

Beginning in the 2013-2014 season Hitechnic introduced 360 degree IR beacon (#HBK2100).  This beacon replaces the previous, 180 degree IR beacon (#FTCBCN).  Both types of beacons are allowed at events during the 2013-2014 season.  However, team's should note that due to differences in the placement of the IR LEDs, the measured output from the new style beacon will be different (typically lower in magnitude) than the measured output from the old style beacon.

Old-style IR Beacon (left) and the new
360 degree new-style beacon.

The new style beacon (right) has 6 IR LEDs placed in a 360 degree circle.  The old style beacon has 3 IR LEDs placed close together (side-by-side).  Because of the differences in geometry, the measured output from the new style beacon is typically lower than the measured output of the older style beacon if the sensor is “looking” at the two beacons head on.  This difference becomes more pronounced at greater distance.  In other words, at farther distances, the measured output of the new style beacon will be noticeably lower than the measured output of an old style beacon at the same distance.

The signal strength of the new style beacons, however, should be strong enough to use for navigation, even at distances of 4 to 8 feet.  Teams might have to adjust their programs to account for the differences in the magnitude of the signal, but there still should be a sufficiently strong signal for them to follow.

Note that the new style beacons have the advantage of 360 degrees of coverage (when running in 360 mode) due to the placement of its 6 LEDs.  The old style beacon does not offer 360 degree coverage since it only had 3 beacons placed on one side of a flat printed circuit board.

Original content (modified 1/28/14)

This year’s game, [FTC BLOCK PARTY!], provides infrared (IR) beacons that can be used as navigational aids for the autonomous operation of a robot.  The light that is emitted by these beacons is not visible to the human eye.  However, a special device such as the HiTechnic IR Seeker (version 2) can be used to detect the IR energy and navigate towards the beacon.

Digital photo of an IR Beacon - 
The three purple lights in the 
center are the infrared LEDs.

The IR beacon is powered by a 9V battery and has three IR LED’s (6 LEDs for the new-style beacon) that flash on and off at a frequency of 1200 Hz.  Although the IR energy is not visible to the unaided eye, a common digital camera (one that does not have an IR filter) should be able to capture the glow from the IR LED’s.

The HiTechnic IR Seeker sensor can be used by your robot to detect and navigate to the flashing IR signal.

The IR seeker measures the strength of the IR signal and also provides directional information.  The area around the beacon is divided into 9 sectors.  The IR seeker indicates which zone (if any) has the strongest IR signal.

LabVIEW and RobotC both contain sample programs on how to use the IR Seeker sensor.  Go to the FTC Toolbox for a summary of these sample programs.

One important fact to note is that the energy that is emitted by the old-style IR beacon is not omnidirectional.  In order to get the strongest measured signal, it is important that the IR Seeker have the most direct line-of-sight possible.  If the IR beacon is placed at a certain height above the floor, then a robot designer should consider placing their IR sensor at the same level, to ensure a good, direct line-of-sight to the IR LEDs.  Also, in order to measure the strongest possible signal, the IR sensor should not have any objects in the way that obstruct the sensor’s line of sight to the LEDs.