here’s a micro controller-based temperature indicator that displays the temperature in the range of –55°C to 125°C. Besides AT89C52 micro controller, it uses a temperature sensor chip and annLCD module. The indicator outputs the calibrated data in digital form. The program for the micro controller is written in C and not in Assembly language. Since C program has well-defined syntax, it far outweighs the merits of the Assembly language program. shows the block diagram of the temperature indicator using micro controller AT89C52. The power supply for the circuit is regulated by IC 7805 and supplied to different parts of the unit. DS1621 is the temperature sensor chip. The micro controller unit (MCU) reads
the temperature from the sensor. The temperature data is compared with certain user-defined temperature values and processed inside the MCU as per the program and then sent to the LCD for display. shows the circuit of temperature indicator using micro controller AT89C52. Working of each section of the circuit is covered in the following paragraphs
Power supply. The power supply unit consists of a step-down transformer (230V AC primary to 0-9V, 250mA secondary), bridge rectifier and voltage regulator. The output of the transformer is fed to bridge rectifier diodes D1 through D4 (each 1N4007). The ripple from the output bridge rectifier is filtered by capacitor C1 and fed to regulator IC 7805. The regulated output is given to the temperature sensor, micro controller unit and LCD module, respectively. When switch S1 is closed, LED1 glows to indicate the presence of power in the system..
Temperature sensor. Temperature sensor chip DS1621 (IC3) is an 8-pin DIP IC. Its pin details are shown in Fig. 3 and the internal block diagram in Fig. 4. The chip can measure temperatures from –55°C to +125°C in 0.5°C increments, which are read as 9-bit values. It can operate off 2.7V to 5.5V. Data is read/written via a 2-wire serial interface. Pins 1 and 2 of the temperature IC are connected to pins 11 and 10 of the micro controller, respectively. The thermal below user-defined low temperature TL. User-defined temperature settings are stored in the non-volatile memory. Temperature settings and temperature readings are all communicated to/from IC DS1621 over a 2-wire serial cable. The most significant bit (MSB) of the data is transmitted first and the last significant bit (LSB) is transmitted last.