Infrared data transmission for mechatronic system control.

Manescu, Mihai ; Cristea, Luciana ; Cotoros, Diana 等

1. INTRODUCTION

Many modern technological products result from integrating mechanical, electrical and computer systems. This combination of technologies is known as mechatronic systems engineering and such mechatronic systems are found in numerous applications (Alciatore, 2005). A mechatronic device is one that is able to perceive the surrounding environment, make appropriate decisions based on that information, and executes the right decisions (take action). Mechatronic as a highly interdisciplinary domain, involve sensors, actuators, data bases, system modelling, locomotion, and system control and data acquisition. Modern mechatronic systems comprise a number of subsystems, which rely heavily on digital data communications. Different levels of complexity of these systems means that the requirements for data communications range from a simple communication between two devices to systems with a large number of subsystems using communication network.

In the construction of the mobile mechatronic systems, the development of robotics and digital circuits lead to the occurrence of new technologies for information transmission. The transmission line is generally implemented using electrical wiring but cam involve a variety of physical medium including radio frequency, infrared, and sound signals. A transmission line provides a physical medium connecting the two systems. Among these technologies, the paper presents the study concerning the data transmission by infrared using USART protocol (Bishop, 2006).

2. THEORETICAL ASPECTS

The receiver construction includes a TSOP17xx circuit, which integrates the IR sensor and performs the conversion and demodulation of the received signal in order to make it compatible with the UART protocol. The data reaching the receiver are decrypted and may be used for controlling certain driving devices or save them on a PC (Moreau, 2000). The receiver communicated with the PC by help of the UART type serial interface. The receiver is a TSO[P.sub.1]738 integrated circuit, consisting of a demodulator, wave-band filter, amplifier and infrared sensor that perceive the infrared radiation (fig.1).

[FIGURE 1 OMITTED]

The transmitter is a LED (TSAL6200) which sends infrared radiation having the wave length of 940nm. The circuit controlling the LED should assure a modulation frequency (on/off) of 38 kHz because only the IR signals of 38 kHz are accepted by the receiving TSOP1738 circuit. This IR interface is able to transmit data with a velocity up to 2400 bps. In the present situation we work with 1200bps.

This modulation assures the removal of the perturbations produced by other IR radiations emission sources. There is a large range of integrated circuits of TSOP1xx type that can be used as a receiver for different signal demodulation frequencies (Tab1.).

An important characteristic of the modulated signal is its duty cycle. In this project, the duty cycle is 75% but it also works with 50%. The modulation is accomplished by help of an ATmega8515 micro-controller using a timer set at 38 kHz.

The demodulated signal is taken over from TSOP1738 and processed by an ATmega162 micro-controller. The demodulated signal is applied at the serial port input (line RX). On the serial interface (line TX) we transmit the hexadecimal code towards the PC, corresponding to each received byte.

The transmitting LED is on 75% of the modulation time. The demodulated signal on the receiver output applied to the serial port Atmega162 input is 0 when the transmitter sends signals and 1 when it does not transmit (LED is off). Data format received on UART is presented in figure 2. The first transmitted bit is the most insignificant one. (lsb).

[FIGURE 2 OMITTED]

3. DATA TRANSMISSION PROGRAMMING

In order to be able to also use the program for other micro-controllers having less power and smaller costs (Attinyll, Attiny13) this is going to use a single Timer both for the accomplishment of the signal modulation (38 kHz) and for the bits transmission (by means of a signal compatible to the serial protocol RS232) with a 1200 bps (1,2kHz) velocity.

Dividing 38/1.2=31.6, we get a constant showing the fact that during the transmission of 1 bit, (logical 1) the signal will oscillate 31.6 times (meaning the signal is modulated) (fig.3).

Theoretically the transmission time of a bit should be 31 times the modulation period. Introducing an "if " instruction before setting the timer constant, the modulation frequency decreases and thus we need to lower also the proportionality constant between the two frequencies.

void timer1_ovf_isr(void)
{
if(cons<=27)//between 26..28
{
TCNT1H = 0xFE; //reload counter high value
TCNT1L = 0x5B; //reload counter low value
}

We experimentally found that a value between 23 and 28 is admissible instead of 31.6. The decreasing of the signal frequency modulation (caused by the "if" instruction does not visibly influence the data transmission.

The main benefit of the Attiny13 micro-controller is the low cost. It does not dispose of the UART interface making thus the programmes development and programming errors detection more difficult. This 8 pins micro-controller includes the following peripherical devices: 1 timer, 2 PWM channels, ADC and SPI.

Attiny13 also contains an 8 bits timer with a prescaler. In order to configure the timer we need to set 3 registers: TCCR0A, TCCR0B, TCNT0, and TIMSK0.

TCCR0A--Timer/Counter Control Register A--TCCR0A By this register we select the operation mode. We initiated it with 0x00 because it is used as a counter.

TCCR0B--Timer/Counter Control Register B--TCCR0B

FOC0A and FOC0B (FOC0A: Force Output Compare A and B) will be set to 0 because we do not want to use the PWM lines (fig.4).

WGM02 is 0 (not using PWM)

CS02:0: Clock Select By these bits we select the impulse source that are going to be counted. These bits can set up the pre-scaler.

In order not to repeat pseudo-randomly generated numbers, we save as many times the reset procedure is initialized. Thus, each time the starting point for generating random numbers is different.

We will transmit two codes. The first one is randomly generated.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

The second one is generated based on the first using a secret function. The same function will be applied by the receiver in order to check the codes validity. The receiver will calculate the function image for the first code and will compare it to the second code received by the IR interface.

no_reset=no_reset+1;
varrand=no_reset;
srand(varrand);srand(varrand);
x
x=rand();
 TR_by_IR(x);
 wait(100);
 TR_by_IR(x+100);
 wait(100);

The connection modality for the IR led and the source is presented in figure 5. Power consumption is 25mW.

4. CONCLUSIONS

This type of transmission can be successfully used in different applications which require the control along not very big distances (8-10 m). The benefits of this transmission type are: low costs of the necessary components, low number of components, the transmitter size is very small, the human operator is not affected in any way. For building the high-performance multicomputer systems high-performance data communication/transmission systems are required as interconnection links between the computers as well as between the accompanying monitoring facilities scattered over the different applications.

Further work will be focused on the data transmission used in automatic inspection systems.

5. REFERENCES

Alciatore, G. & Histand, B. (2005), Introduction to Mechatronics and Measurement Systems, McGraw-Hill Science/Engineering/Math; 3 edition, 2005

Bishop, H., R. (2006), Mechatronics an Introduction, CRC Taylor&Francis Group

Moreau, B., N. Tomatis et al. (2000). Multimodal Web Interface for Tasks Supervision and Specification. Proceedings of SPIE Vol. 4195: Telemanipulator and Telepresence VII. Boston, USA

***(2008) www.atmel.com, Atmel QTouch Library 2.0, Accesed on:2009-01-15

***(2008) http://www.robotroom.com/Infrared555.html, David Cook ROBOT ROOM Accesed on:2009-01-28

***(2007) http://www.sigterm.de Tools of Trade for World Domination Accesed on:2009-01-30

Tab. 1. Integrated circuits capable of demodulating IR signalsf
according to the modulation frequency


Type fo Type fo

TSOP1730 30 kHz TSOP1733 33 kHz
TSOP1736 36 kHz TSOP1737 36.7 kHz
TSOP1738 38 kHz TSOP174Q 40 kHz
TSOP1756 56 kHz