ESP8266 Range Finder using HC-SR04 and PCF8574AP LCD

Overview 

The HC-SR04 is an ultra-sonic range finder. It use sound wave at the speed of 340m/s that travel in air to measure any detected obstacle. That sound wave signal will travels back whenever there is a barrier created by any object. It uses a speaker that propagates an ultra-sonic signal that human ears could not hear. The detector is a microphone circuit that has an amplifier. The distance of the detected object is the time the sound wave travel divides by 2. The measurement formula is,

Test distance = (high level time * velocity of sound ) / 2.

The velocity of sound is 340m/s. 

 

Distance Measurement

 

The table below summarizes the features of the HC-SR04 Distance Sensor.

HC-SR04 Parameters

 This Arduino module is very popular because of its low cost, easy-to-use, etc.

The Arduino HC-SR04 Module

The Arduino HC-SR04 Module

 

The high level time is the input high time creates by the echo pin of the HC-SR04 Ultra-Sonic Range Finder Module. That time duration is measure in micro-seconds, and the Test distance is measure in cm. To measure that time duration, the micro-controller need to process it precisely. In Arduino, it has the pulseIn function that can measure any logic level ( HIGH or LOW) time at any specific input pins. 

ESP8266 Interfaces with the PCF8574AP and HC-SR04 

In this example, I use the HC-SR04 to measure the distance. The result will show on a 16x2 character LCD controlled by the PCF8574AP I/O expansion chip. Because the ESP-12E has a limited of digital I/O pins. On the other hands, Some pins of this IoT module are connected to other peripherals. 

The 7-bit Arduino slave address of the PCF8574AP here is 0x38. Commonly they use the PCF8574T Arduino Two-Wire LCD module that has different slave address.

Circuit Connection

It needs a small breadboard to build the circuit. Connect the all components as follow.

• Connection between ESP-12E and HC-SR04

HC-SR04	ESP12-E
« 1 2 3 4 »
VIN	VCC
Trig	D6 (GPIO 12)
Echo	D5 (GPIO 14)
GND	GND

• Connection between ESP-12E and PCF8574AP LCD

ESP-12E	PCF8574AP LCD
« 1 2 3 4 »
GND	GND
D1 (GPIO 12)	SCL
D2 (GPIO 14)	SDA
VIN	VCC

ESP8266 Arduino Source Code

I use the Arduino LiquidCrystal_I2C library. It's originally developed to work with the Arduino AVR. However for the ESP8266, it is compatible. It works fine.

#include <Wire.h> 
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x38,16,2); 

#define trigPin D6
#define echoPin D5

/*
PWM OUTPUT 0-25000uS in which 1cm=50uS
*/
long   duration;
int   distance;

void setup() {
  pinMode(trigPin,OUTPUT);
  pinMode(echoPin,INPUT);
  lcd.init();
  // Print a message to the LCD.
  lcd.backlight();
  lcd.clear();
  lcd.setCursor(0,0);
  lcd.print("ESP-12E PCF8574AP");
  lcd.setCursor(0,1);
  lcd.print("and HC-SR04");
  delay(10000);
  lcd.clear();
}

void loop() {
  digitalWrite(trigPin,LOW);
  delayMicroseconds(7);
  // Set the trigPin high for 10 uS
  digitalWrite(trigPin,HIGH);
  digitalWrite(trigPin,HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin,LOW);
  duration=pulseIn(echoPin,HIGH);
  // Calculation for distance
  if(duration<=25000)
  distance = duration * 0.034 / 2;
  else
  distance=0;
  lcd.setCursor(0,0);
  lcd.print("Time: " + String(duration) + "uS  ");
  lcd.setCursor(0,1);
  lcd.print("Distance: " + String(distance) + "cm  ");  
  delay(500);
}

 

 

Pictures

I can not find these module at any online circuit simulator now. Currently WOKWI only support some high-end board. 

 

Distance Measurement