Interfacing PIR sensor to 8051

Interfacing PIR sensor to 8051 microcontroller.

PIR sensors are widely used in motion detecting devices. This article is about interfacing a PIR sensor to 8051 microcontroller. A practical intruder alarm system using PIR sensor and 8051 microcontroller is also included at the end of this article. Before going in to the core of the article, let’s have a look at the PIR sensor and its working.

PIR sensor.

PIR sensor is the abbreviation of Passive Infrared Sensor. It measures the amount of infrared energy radiated by objects in front of it. They does not emit any kind of radiation but senses the infrared waves emitted or reflected by objects. The heart of a PIR sensor is a solid state sensor or an array of such sensors constructed from pyro-electric materials. Pyro-electric material is material by virtue of it generates energy when exposed to radiation.Gallium Nitride is the most common material used for constructing PIR sensors. Suitable lenses are mounted at the front of the sensor to focus the incoming radiation to the sensor face. When ever an object or a human passes across the sensor the intensity of the of the incoming radiation with respect to the background changes. As a result the energy generated by the sensor also changes. Suitable signal conditioning circuits convert the energy change to a suitable voltage output. In simple words the output of a PIR sensor module will be HIGH when there is motion in its field of view and the output will be LOW when there is no motion.

DSN-FIR800 is the PIR sensor module used in this project.Its image is shown above. It operates from 4.5 to 5V supply and the stand by current is less than 60uA. The output voltage will be 3.3V when the motion is detected and 0V when there is no motion. The sensing angle cone is 110° and the sensing range is 7 meters. The default delay time is 5 seconds. There are two preset resistor on the sensor module. One is used for adjusting the delay time and the other is used for adjusting the sensitivity. Refer the datasheet of DSN-FIR800 for knowing more.

Interfacing PIR sensor to 8051.

The 8051 considers any voltage between 2 and 5V at its port pin as HIGH and any voltage between 0 to 0.8V as LOW. Since the output of the PIR sensor module has only two stages (HIGH (3.3V) and LOW (0V)) , it can be directly interfaced to the 8051 microcontroller. The circuit diagram for interfacing PIR sensor to 8051 microcontroller is shown below.

The circuit shown above will read the status of the output of the PIR sensor and switch ON the LED when there is a motion detected and switch OFF the LED when there is no motion detected. Output pin of the PIR sensor is connected to Port 3.5 pin of the 8051. Resistor R1, capacitor C1 and push button switch S1 forms the reset circuit. Capacitors C3,C4 and crystal X1 are associated with the oscillator circuit. C2 is just a decoupling capacitor. LED is connected through Port 2.0 of the microcontroller. Transistor Q1 is used for switching the LED. R2 limits the base current of the transistor and R3 limits the current through the LED. Program for interfacing PIR sensor to 8051 is shown below.

Program.

PIR EQU P3.5  LED EQU P2.0  ORG 00H  CLR P2.0           SETB P3.5  HERE:JNB PIR, HERE       SETB LED  HERE1:JB PIR,HERE1        CLR LED  SJMP HERE  END  

The status of the output of the PIR sensor is checked using JNB and JB instructions. Code “HERE:JNB PIR, HERE” loops there until the output of the PIR sensor is HIGH. When it becomes HIGH it means a motion detected and the program sets P2.O HIGH in order to make the LED ON. The output pin of the PIR sensor remains HIGH for 5 seconds after a motion is detected. Code”HERE1:JB PIR,HERE1″ loops there until the output of the PIR sensor becomes LOW. When it becomes LOW the loop is exited and Port 2.0 is made LOW for switching OFF the LED. Then the program jumps back to label “HERE” and the entire cycle is repeated.

Intruder alarm using PIR sensor and 8051 microcontroller.

This is just a serious practical application of PIR sensor and 8051 microcontroller. This circuit counts every intrusions and displays the number on intrusions on a 16×2 LCD display. An alarm is also made for 5 seconds on every intrusion. A relay is used for switching the alarm buzzer. Additional loads like bulb, solenoids etc can also be switched using the same relay. The circuit diagram of the intruder alarm using PIR sensor and 8051 microcontroller is shown below.

Circuit diagram.

The circuit diagram of the PIR intruder alarm is shown above. The data pin D0 to D7 of the LCD module are connected to Port 0 of the microcontroller. The Port 0 of 8051 is open drain and it will not work properly as an output port with out external pull up resistors. The resistor network R1 is used for pulling the Port 0 up. The control pins Rs, Rw and E of the LCD are connected to P2.7, P2.6 and P2.5 pins of the microcontroller. Output of the PIR sensor is connected to P3.5 of the microcontroller. P2.0 of the microcontroller is used for controlling the relay. Transistor Q1 is used for switching the relay. Resistor R7 limits the base current of the transistor. D5 is a freewheeling diode. R0 is a pull up resistor. Since a relay is used for driving the buzzer you have the flexibility to use other loads like electric bulb, solenoid, motor etc at the output instead of the buzzer. The program for interfacing PIR sensor to 8051 is shown below.

Program.

PIR EQU P3.5  RS EQU P2.7  RW EQU P2.6  E EQU P2.5  ORG 00H  MOV DPTR,#LUT  SETB P3.5  CLR P2.0  MOV R7,#00D  ACALL SPLIT  MAIN:ACALL DINT  ACALL TEXT1  ACALL LINE2  ACALL TEXT2  ACALL TEXT3  ACALL NUM    HERE:JNB PIR,HERE  SETB P2.0  INC R7  ACALL SPLIT  ACALL DINT  ACALL TEXT1  ACALL LINE2  ACALL TEXT4  ACALL TEXT3  ACALL NUM  HERE1:JB PIR,HERE1  CLR P2.0  SJMP MAIN    SPLIT:MOV A,R7  MOV B,#10D  DIV AB  MOV R6,B  MOV B,#10D  DIV AB  MOV R5,B  MOV B,#10D  DIV AB  MOV R4,B  RET  TEXT1: MOV A,#80D  ACALL DISPLAY  MOV A,#73D  ACALL DISPLAY  MOV A,#82D  ACALL DISPLAY  MOV A,#32D  ACALL DISPLAY  MOV A,#83D  ACALL DISPLAY  MOV A,#69D  ACALL DISPLAY  MOV A,#78D  ACALL DISPLAY  MOV A,#83D  ACALL DISPLAY  MOV A,#79D  ACALL DISPLAY  MOV A,#82D  ACALL DISPLAY  RET    TEXT2: MOV A,#83D  ACALL DISPLAY  MOV A,#67D  ACALL DISPLAY  MOV A,#65D  ACALL DISPLAY  MOV A,#78D  ACALL DISPLAY  MOV A,#73D  ACALL DISPLAY  MOV A,#78D  ACALL DISPLAY  MOV A,#71D  ACALL DISPLAY  MOV A,#46D  ACALL DISPLAY  MOV A,#46D  ACALL DISPLAY    RET    TEXT3: MOV A,#73D  ACALL DISPLAY  MOV A,#78D  ACALL DISPLAY  MOV A,#84D  ACALL DISPLAY  MOV A,#82D  ACALL DISPLAY    RET    TEXT4: MOV A,#65D  ACALL DISPLAY  MOV A,#76D  ACALL DISPLAY  MOV A,#69D  ACALL DISPLAY  MOV A,#82D  ACALL DISPLAY  MOV A,#84D  ACALL DISPLAY  MOV A,#33D  ACALL DISPLAY  MOV A,#33D  ACALL DISPLAY  MOV A,#33D  ACALL DISPLAY  MOV A,#33D  ACALL DISPLAY  RET    NUM:MOV A,R4  ACALL ASCII  ACALL DISPLAY  MOV A,R5  ACALL ASCII  ACALL DISPLAY  MOV A,R6  ACALL ASCII  ACALL DISPLAY  RET    DINT:MOV A,#0FH  ACALL CMD  MOV A,#01H  ACALL CMD  MOV A,#06H  ACALL CMD  MOV A,#83H  ACALL CMD  MOV A,#3CH  ACALL CMD  RET    LINE2:MOV A,#0C0H  ACALL CMD  RET    CMD: MOV P0,A  CLR RS  CLR RW  SETB E  CLR E  ACALL DELAY  RET    DISPLAY:MOV P0,A  SETB RS  CLR RW  SETB E  CLR E  ACALL DELAY  RET    DELAY: CLR E  CLR RS  SETB RW  MOV P0,#0FFh  SETB E  MOV A,P0  JB ACC.7,DELAY  CLR E  CLR RW  RET    ASCII: MOVC A,@A+DPTR  RET    LUT: DB 48D  DB 49D  DB 50D  DB 51D  DB 52D  DB 53D  DB 54D  DB 55D  DB 56D  DB 57D  

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