Localized IR communications with Thymio II
Document typeMaster thesis (pre-Bologna period)
Rights accessOpen Access
[ANGLÈS] The goal of this master project is to develop an IR communication protocol for the robot Thymio II in order to use the seven IR proximity sensors existing in the robot, used to detect obstacles around it) to exchange data between several of them. We must achieve this goal with the current electronic design, so we can not add or change any hardware of the robot. The protocol must fulfil the following characteristics: • Exchange 8 bits of data and some bits of header per frame. • Transmit and receive data without disturbing the obstacle detection around the robot. • Work with up to ten robots in a changing topology. The developed protocol uses a Differential-PPM which encodes the data as the period of a two pulses signal using the following expression: Period=OFFSET+(GAIN*data) • OFFSET is the minimum period of the signal. • GAIN is the difference between two consecutive periods. We can generate these signals using the Output Compare module of the microcontroller and decode it using its Input Capture module. As a Network Access Protocol a kind of CSMA-CA has been developed, but changing a little bit its features in order to make it fit with our system needs and behaviour. After testing the developed system under different topologies and conditions, the following results were obtained: • DecodingErrorRate=0.225% in a two nodes network. • LostPacketRate(LPR)=0% between tree robots. • LPR=0.874% between five robots. • LPR=10% between seven robots. • Maximum transmission rate= 40cm We can see that the maximum number of robots of the system is limited by the physical place around the robot and not for the error probability of the protocol. Some additional functionalities of the system are the possibility to estimate the distance and bearing between robots by processing the width of the received pulses.
Projecte realitzat en el marc d’un programa de mobilitat amb la École polytechnique fédérale de Lausanne