Microcontroller based wireless temperature and heartbeat read out suitable for a operation in a small office/home environment . This system is suitable to operate with Visual LCD. Many individuals or organisations may, for various reasons,wish to use electronic surveillance technique at some time or another. This idea is to use off the shelf RF Tx/Rx modules. The weather keeps us continually occupied. Some people have even made it their profession. At home too,we like to measure all kinds of things related to our climate.That is why weather stations are available in all types and sizes.
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| Block Diagram |
If we want to know the temperature inside and outside then purpose built indoor/outdoor thermometers are available. In the past the outside sensor of these weather stations was connected with a wire, it is now fairly standard to use RF transmission for this data. The wireless transmitters units usually make use of the 315-MHz band. These modules, once a rare commodity, are now widely and cheaply available. In this particular discussion, we shall be using ASK(Amplitude Shift Keying) based TX/RX pair operating at 315 MHz. The transmitter module accepts serial data at a maximum of 2400bps. They are directly interfaced to a microcontroller. At the RX end, the receiver microcontroller receives the signal via the RF receiver module,decodes the serial data and reproduces the original data in the temperature and Heart Beat format.
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| Circuit for 5 volt generation from AC supply |
Temperature Sensor
Temperature is one of the fundamental physical variables in most chemical and process control applications. Accurate and reliable measurements of the temperature is important in nearby all process control applications. Temperature sensors can be analog or digital. Some of the most commonly used analog temperature sensors are : thermocouples, resistance temperature detector ( RTD)s and thermistors. Digital sensors are in the form of integrated circuits. The choice of a sensor depends on the accuracy, the temperature range, speed of response, thermal coupling, the environment (chemical, electrical, physical) and the cost. A popular voltage output analog integrated circuit temperature sensor is LM35DZ,manufactured by National Semiconductor. This is the 3 pin analog output sensor which provides a linear output voltage of 10 mV/degree Celsius. The temperature range is 0 to 100 degree Celsius, with an accuracy of +-1.5 degree Celsius.
Heart Beat Signalling
The heart beat signal is obtained by LED and LDR combination. Pulses form hand interrupts the Light reaching the LDR and the signal is read by microcontroller, The RF signal is transmitted by transmitter in a digital format. This circuit uses Manchester encoding to avoid a long trail of zero. The protocol is well defined for different devices types ensuring compatibility with your whole entertainment system 5 bit address and 6 bit command length. Constant bit time of 1.778ms bits are of equal length of 1.778 ms in this protocol, A logical zero is represented by a pulse in the first half of the bit time. A logical one is represented by a pulse in the second half of the bit time.
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| Transmitter circuit diagram |
PIC Microcontroller
Microcontrollers contains all the required for a processor system in one chip, a CPU,memory and I/O. A complete system can be built therefore built using one MCU chip and a few I/O devices such as a keypad, display and other interfacing circuits. Most of the pins are for input and output, and arranged as 5 ports: PORTA( 5 pins), PORTB( 8 pins), PORTC( 8 pins), PORTD( 8 pins), PORTE( 3 pins), giving a total of 32 I/O pins. These can all operate as simple digital I/O pins, but most have more than one function and the modes of each is by initializing various control registers within the chip. Port B is used for the downloading to the program to the chip flash ROM and RB0 and RB4-RB7 can generate an interrupt. Port C gives access to timers,while Port D can be used as a slave port ,With port E providing the control pins for this function.
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| Receiver circuit diagram |
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