Ultrasonic Distance Sensor HC-SR04 Interfacing with 8051

          In this tutorial you will learn how to interface Ultrasonic Distance Measurement Sensor with AT89S52. Ultrasonic ranging module HC - SR04 provides 2cm - 400cm non-contact measurement function.the ranging accuracy can reach to 3mm. The modules includes ultrasonic transmitters, receiver and control circuit.I also Provide you complete Project code you can download it from the bottom of the page.

Now working of HC-SR04 as follow:

1. Send 10us HIGH pulse on TRIG pin of HC-SR04.
2. The sensor sends out a “sonic burst” of 8 cycles.and detect whether there is a pulse signal back.If there is an obstacle in-front of the module, it will reflect the ultrasonic burst.
3. If the signal is back, ECHO output of the sensor will be in HIGH state (5V) for a duration of time taken for sending and receiving ultrasonic burst. Pulse width ranges from about 150μS to 25mS and if no obstacle is detected, the echo pulse width will be about 38ms.

Pinout of HC-SR04:

HC-SR04 Front view

• VCC –   5V Power supply.
• TRIG –  Trigger Pin connect to the P1.1 of AT89S52.
• ECHO – Echo Pin connect to the P1.0 of AT89S52.
• GND –   -0V  Ground.

Timing Diagram of HC-SR04:

Timing Diagram of HC-SR04

Circuit Diagram:

Programming Steps:

1. Provide TRIGGER to Ultrasonic module HC-SR04.
2. Listen for Echo.
3. Start Timer when ECHO HIGH is received.
4. Stop Timer when ECHO goes LOW.
5. Read Timer Value.
6. Convert it to Distance.

        Here Trigger pin of HC-SR04 is connected P1.1 of AT89S55 which is output pin.Echo pin is connected to P1.0 of AT89S52 which is Input. 

sbit Echo = P1^0;

sbit Trig  = P1^1;

Timer 0 is used in 16-bits mode for measuring time.

TMOD |= 0x01;//Timer 0 in 16-bit mode.

Now Send 10us HIGH pulse on TRIG pin of HC-SR04.

Trig = 1;

delay_us(10);

Trig = 0;

Wait for rising edge at echo pin of HC-SR04.

while(Echo == 0);

Start Timer 0 and clear timer count register.

TR0=1;

TL0=TH0=0;

Now wait for falling edge at Echo pin and stop timer and Calculate time.

while(Echo == 1)

{

if(TF0 == 1)//timer over if no obstacle is detected

break;

}

TR0=0;

TF0 = 0;

//Calculate number of count

Count = TL0 + TH0*256;

//Calculate total time in uS.

Time = Count*1.085;

//As per datasheet of HC-SR04 Distance is in Centimeter.

Distance = Time/58;

//The distance is then sent using serial communications.

Download:

You can download entire project files here.

Interfacing HC-SR04 with 8051 Microcontroller - Keil uVision.