Spring 2016: 3DoT Spider-Bot IR Transmitter and Receiver Research

By: Christopher Hirunthanakorn (Missions, Systems and Test Engineer)

Introduction:

In order to determine which optical transmitter and detector would be the best solution for implementing the game of tag between the 3DoT David and 3DoT Goliath,, the following research on IR transmitters and detectors was done. It started with learning about the various types of transmitter and detector systems that are available such as pre-made transmitters and passive infrared sensors (PIR sensor). From there, specific characteristics were researched such as range, sensitivity, power consumption, and size. Afterwards, the pros and cons of using a basic IR transmitter and detector are listed to be used for discussion.

Related Requirement:

Because this research was done before the type of tagging system to be used was decided on by both teams, this is the most relevant requirement.

The 3DoT David shall use an infrared LED emitter and infrared detector for the tagging system in the game of tag.

Types of IR systems:

The various types of transmitter and detector systems can be broken down into three major groups, which are the basic systems, data transmission systems, and the motion detection systems. The basic systems are composed of just an infrared emitter and an infrared detector. The emitter is typically an IR LED that emits light in the 850 nm to 950 nm range(1). The detector is usually a photosensitive transistor that conducts current when IR light is detected. Data transmission systems are the IR transmitters and receivers that are typically found in remote controls. They are used to send data and are more expensive than the basic systems because they are pre-made circuit boards. They have better range and sensitivity than the basic systems(2). Unfortunately, they are not suited for the game of tag because those features are beyond the scope of the project. The final type of IR transmitter and detector systems are the PIR sensors. They are typically used in motion detection applications and passively detect changes in reflected IR waves(3). The PIR sensor would have been the most promising solution except for the issue with false positive results when the robot moves or turns. Once this was done, more detailed research was performed on the basic system of IR transmitters and detectors.

After additional research, more information on the range, sensitivity, and ways to improve those characteristics was found. The normal range of the IR transmitter is two to four feet when it is supplied with the rated current. It is possible to improve the range of the transmitter by amplifying the current above the rated value as mentioned in several forum posts(4). It requires building a small circuit with a transistor to provide the necessary current. As for the sensitivity of the IR detector, some types have a large viewing angle. This means that the detector has a wide field of vision for detecting any infrared light. The large viewing angle could cause issues for the game of tag since it is possible for the detector to trigger when the transmitter of the other robot is not pointed in the right direction to hit the detector. After searching the internet, two possible solutions to issue were found. One solution involves picking an IR transmitter with a narrow viewing angle and utilizing a collimator to decrease the spread of the infrared light(5). It will make sure the infrared light is directed in the desired direction and improves the range of the transmitter(6). The other solution is to create an enclosure around the detector so that it will narrow down the viewing angle and modify the sensitivity to the level that suits the game of tag.

Conclusion:

When considering the use of an IR transmitter and detector for the tagging system, the best solution was the IR emitter and detector combination. Our robot needed the sensitivity and controllable intensity that this combination provides because the range of the tagging system must be customizable. The other IR systems did not provide this amount of control and were eliminated. We are currently considering the solution that involves using a lens to focus the intensity of the IR emitter.

Work cited:

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