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LCD based digital alarm clock with digital thermometer using 8051 microcontroller (AT89C51)


Developed By: 
Himanshu Choudhary

This project works as a digital clock wherein a user can also set alarm. Additionally, it also works as a digital thermometer to specify the ambient temperature. Both, the clock and temperature are displayed on a 16x2 LCD screen using the 8051 microcontroller (AT89C51). AT89C51 is an eight bit controller which belongs to the 8051 family of microcontrolers.

LCD based digital alarm clock with digital thermometer using 8051 microcontrolle



Celsius scale thermometer displays the ambient temperature through a LCD display. It consists of two sections. One is that which senses the temperature. This is a LCD based Digital Alarm clock with thermometer function temperature sensor LM 35. The other section converts the temperature value into a suitable number in Celsius scale which is done by the ADC0804. A digital thermometer can be easily made by interfacing a temperature sensor to the microcontroller AT89C51. The temperature sensor used in the project isLM35. The LM 35 IC generates a 10mV variation to its output voltage for every degree Celsius change in temperature. The Output of the temperature sensor is analog in nature so we need an analog to digital convertor for converting the analog input to its equivalent binary output.ADC 0804 is an analog to digital convertor IC used in the project. 0804 is a single channel convertor which converts the analog input up to a range of 5V to an equivalent 8-bit binary output.  

This project incorporates the functionality of a digital clock and a digital thermometer. The digital clock works in 12 hour mode and is configured by programming the 8051 microcontroller (AT89C51). The program uses a delay function for producing a delay of 1 second. The clock and alarm times can be set through a set of external tactile switches.


The digital thermometer employs a temperature sensor LM35. The sensor responds to the temperature change by giving varying output. These analog signals of LM35 are converted to digital equivalent by ADC0804. The reference voltage (Vref) should be set properly corresponding to the desired temperature range. The data bits are taken as input by the microcontroller at port P0. The microcontroller AT89C51 also gives control signals to ADC0804.

Circuit Diagram



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