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Gsm Based Temperature Measurment System Computer Science Essay

Short bursts of data once restricted to fixed LANs and WANs are now being delivered to mobile devices to boost productivity and improve customer service. Wireless Short Message Service (SMS), is the vehicle for this communication. SMS messaging has been one of the success stories of the mobile phone industry over the past three years.

Now a days it has become a major concern in monitoring the real time temperature for a remote area particularly in controlling the switch which is temperature controlled.

The real time temperature controlled switches are used to control some devices depending on the predefined temperature. The current temperature of the place is endlessly monitored by the microcontroller through the temperature sensor. If the current temperature of the place exceeds the stored value then the microcontroller will send the signal to relay. As the relay operates the status is displayed on the LCD as well as it is sending an SMS message to the authorized person using GSM module. The status of that place is monitored. If the user wants to monitor at a particular time he can send an SMS to the system by circulation user ID then the system will read this SMS and sends the status of the place.

Temperature is a Physical parameter which is converted into an electrical parameter by a device called Temperature Transducer. Transducer is also referred to as a sensor.

The commonly used transducer produces an output voltage, current, capacitance and resistance. However we need to convert these signals to voltage in order to send an input to an A-D converter. This conversion is commonly called signal conditioning. Signal conditioning can be a current to voltage conversion or signal amplification.

For example, the output of thermistor is change in resistance with change in temperature. The change in resistance must be signal conditioned into voltage in order to use an ADC.

The most important parameter of an ADC is resolution. The higher resolution ADC provides a smaller step size, where step size is the smallest change that can be discerned by an ADC. In addition to resolution, conversion time is another major factor in judging an ADC. Conversion time is defined as the time taken by an ADC to convert the analog signal to a digital signal.

The ADC chips are either parallel or serial ADC. In parallel ADC, we have 8 or more pins dedicated to bringing out the binary data, but in serial ADC we have only one pin for data out.

Microcontroller is the central component which reads data (temperature) from ADC and from the keypad switches display the temperature and necessary on LCD (Liquid Crystal Display) and controls the Relay.

In order to do all the activities a program (sequence of instruction) must be written for the microcontroller. This program is called firmware. In order to execute the program, Microcontroller requires basic configuration like 5V regulated power supply, clock, and reset circuit.

16*2 (2 line of 16 character) LCD is used for displaying temperature and relay status. It provides easy user interface. It needs to initialize before displaying data. This initialization is done by Microcontroller.

Relay is used to control external device. (Cooler/heater) Since microcontroller does not provide sufficient current, hence relay driver is required.

Keypad switches are used to change the threshold values and see the maximum and minimum temperature.

Semen’s GSM/GPRS Smart Modem has a multi-functional and it is ready to use. It has a rugged unit that can be embedded or plugged into any application. It can be controlled. The Smart Modem can be customized to various levels by using the standard AT commands and it is fully type-approved. The Smart Modem can speed up the operational time with full range of Voice, Data, Fax and Short Messages (Point to Point and Cell Broadcast).It also supports GPRS (Class 2*) for spontaneous data transfer.

Micro controller:

The Atmel AT89C51 is an 8051-based Fully Static 24MHz CMOS controller with 32 I/O Lines, 2 Timers/Counters, 6 Interrupts/2 Priority Levels, UART, Three-Level Program Memory Lock, 4K Bytes Flash Memory, 128 Bytes On-chip RAM.

Sampling Rates:

Resistance thermometers, also called resistance temperature detectors or resistive thermal devices (RTDs), that is exploit the predictable change in electrical signal. Some materials with only changing for temperature. As they are almost invariably made of platinum, they are often called platinum resistance thermometers (PRTs). It is slowly reduce the thermocouples in many industrial applications below 600 °C, due to higher accuracy and repeatability.

It is a basically temperature sensitive resistor.

Choice of ADC:

The ADS0804 can acquire and convert 12 bits to within ±0.5 LSB in 25µs max while consuming only50mW max. Laser-trimmed scaling resistors provide the standard industrial ±10V input range and channel-to-channel matching of ±0.1%. The ADS0804 is a low-power 12-bit sampling A/D with a four channel input multiplexer, S/H, clock, reference, and a parallel/serial microprocessor interface. It can be configured in a continuous conversion mode to sequentially digitize all four channels. The 28-pin ADS0804 is available in a plastic 0.3" DIP and in a SOIC; both fully specified for operation over the industrial–40 ºC to +85 ºC range.

Vital role of GSM mode:

GSM is one of the latest mobile technologies using Smart Modem. It can easily be interfaced to embedded microcontrollers. Using this technology everything is going to be automated and with this technology we can access the devices remotely. We can identify the people, vehicles etc in anywhere of the world using GSM and GPS.

Microcontroller and IC’s require 5V regulated power supply, which is obtained from 230V AC by using step down transformer, rectifier, filter and regulators.

Software:

KEIL Uv2 IDE.

EMBEDDED C PROGRAMMING LANGUAGE.

ATMEL PROGRAMMER.

Tools for schematic design:

1. CAPTURE CIS (ORCAD)

Hardware:

ATMEL 89C51 controller,

ADC 0804,

LM 35 TEMPERATURE SENSOR,

RELAY DRIVER,

LCD,

PCB for microcontroller unit, Reset switches, resistors etc,

RELAY,

Crystal 11.0592 MHz

Working Principle:

When the power is applied to microcontroller, it initializes GSM MODEM, LCD, ADC0804 and Relay Driver. Then it reads the temperature from ADC 0804 and transmits to GSM. Simultaneously it compares the temperature with Threshold values (a High and Low Threshold). If it crosses the threshold values a Controller (Relay) will be activated.

The threshold values can be changed by Entering into Settings Mode (by pressing INC and then DEC buttons). The highest and lowest temperature over a period can be viewed by pressing Settings Button.

CHOICE OF REAL TIME SCHEDULING ALGORITHM:

There are basically four types of real times scheduling algorithm

Round Robin

Round Robin with interrupt

RTOS( Real Time Operating System)

Round Robin:

It is the simplest algorithm. The Round Robin algorithm is characterized by the absence of interrupts. The algorithm consists of a main loop that checks each I/O device in turn and Service them if needed. it cannot suffer from shared data problems. Latency is limited by the maximum duration of a loop cycle. Attractive for simple environments. At the same time the disadvantage for the algorithm is it cannot set priorities. Its worst case wait for an important task code is the sum of execution time of all the other task code.

Round Robin with interrupt:

The main advantage of Round Robin with interrupt routines deals with the very urgent needs of devices. Interrupt routines set flags to indicate the interrupt happened. Main while loop polls the status of the interrupt flags and does any follow up process required by a set flag. It moves more control over priority.

On the other hand the disadvantage of round robin with interrupt algorithm is

Most complicated than Round-Robin because of this context problems can occur.

RTOS:

The advantage of RTOS is interrupts signal the need for follow-up tasks. But, unlike Function-Queue Scheduling, this is handled by the Real-Time Operating System and not by the interrupt routines manipulating flags or a queue. Instead of a loop deciding what to do next the RTOS decides. One follow-up task can be suspended by the RTOS in favouring of performing a higher priority task.-Queue. Suspension of tasks allows the worst case wait for the highest priority item to be zero. Built-in scheduling mechanism yields a system with very stable response characteristics even when changes to the code occur. Its widely available for purchase.

This embedded system is using Round Robin Scheduling as real time scheduling algorithm. The device is used to control only the temperature inside the steel container and so round robin architecture can be set here. And the measured temperature needs to display on the LCD display.

Failure conditions:

Long-term increase or decrease in operating temperature

Air-conditioning failure leads to equipment overheating

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