I am building an IoT system to measure the distance from two individual points by using two HC-SR04 ultrasonic sensors and two 16x2 I²C LCD displays to show each sensor’s reading separately.
Sensor 1 measures the distance, and the result is displayed on LCD 1. Sensor 2 measures the distance after a short delay, displayed on LCD 2. Both readings are also printed on the Serial Monitor for debugging and logging.
I have used Arduino UNO, two HC-SR04 ultrasonic sensors for measuring distances, two 16x2 LCD displays with I²C interface (PCF8574-based) to show each sensor’s distance readings independently.
Shared I²C communication lines (A4, A5) for both LCDs, with unique I²C addresses (0x27 and 0x20).
I am building an IoT system to measure the distance from two individual points by using two HC-SR04 ultrasonic sensors and two 16x2 I²C LCD displays to show each sensor’s reading separately.
Sensor 1 measures the distance, and the result is displayed on LCD 1. Sensor 2 measures the distance after a short delay, displayed on LCD 2. Both readings are also printed on the Serial Monitor for debugging and logging.
I have used Arduino UNO, two HC-SR04 ultrasonic sensors for measuring distances, two 16x2 LCD displays with I²C interface (PCF8574-based) to show each sensor’s distance readings independently.
Shared I²C communication lines (A4, A5) for both LCDs, with unique I²C addresses (0x27 and 0x20).
In the effort to design this system, I developed the below code. I have tested this code on Tinkercad platform for simulation. But this code shows error Tinkercard that "Invalid header file". Altough, I have verified that two system (left senor + left LCD) and (right sensor + right LC) works fine individually without any error by executing a sample code. I also confirmed that each component works individually by executing a sample code. But when I tried to combine the two systems (using the below mentioned code) I am getting error that "Invalid header file". I
Here, I am sharing the image of circuit diagram
The code I built which shows me the error:
#include <Wire.h>
#include <LiquidCrystal_I2C.h>
// I2C LCD addresses
#define LCD_ADDR1 0x27 // LCD #1 (left)
#define LCD_ADDR2 0x20 // LCD #2 (right)
// LCD objects
LiquidCrystal_I2C lcd1(LCD_ADDR1, 16, 2);
LiquidCrystal_I2C lcd2(LCD_ADDR2, 16, 2);
// Ultrasonic pins
#define TRIG1 A2 // Sensor 1: TRIG=A2, ECHO=A3
#define ECHO1 A3
#define TRIG2 A0 // Sensor 2: TRIG=A0, ECHO=A1
#define ECHO2 A1
// Ping helper (with timeout)
unsigned long pingUS(uint8_t trig, uint8_t echo, unsigned long timeoutUS = 50000UL) {
digitalWrite(trig, LOW); delayMicroseconds(2);
digitalWrite(trig, HIGH); delayMicroseconds(10);
digitalWrite(trig, LOW);
return pulseIn(echo, HIGH, timeoutUS);
}
void setup() {
Serial.begin(9600);
// Pins
pinMode(TRIG1, OUTPUT); digitalWrite(TRIG1, LOW);
pinMode(ECHO1, INPUT);
pinMode(TRIG2, OUTPUT); digitalWrite(TRIG2, LOW);
pinMode(ECHO2, INPUT);
// I2C + LCDs
Wire.begin(); delay(50);
lcd1.begin(16, 2); lcd1.backlight(); lcd1.clear();
lcd1.setCursor(0,0); lcd1.print("Sensor1 Dist:");
lcd1.setCursor(0,1); lcd1.print("Sensor1 Dist:");
lcd2.begin(16, 2); lcd2.backlight(); lcd2.clear();
lcd2.setCursor(0,0); lcd2.print("Sensor2 Dist:");
lcd2.setCursor(0,1); lcd2.print("Sensor2 Dist:");
}
void showReading(LiquidCrystal_I2C &lcd, float cm, float inch) {
// cm line
lcd.setCursor(9, 0);
if (isnan(cm)) lcd.print(" --- ");
else { char b1[10]; dtostrf(cm, 6, 1, b1); lcd.print(b1); lcd.print("cm"); }
// inch line
lcd.setCursor(9, 1);
if (isnan(inch)) lcd.print(" --- ");
else { char b2[10]; dtostrf(inch, 6, 1, b2); lcd.print(b2); lcd.print("in"); }
}
void loop() {
// --- Sensor 1 (sequential) ---
unsigned long us1 = pingUS(TRIG1, ECHO1);
float cm1 = NAN, inch1 = NAN;
if (us1 > 0) { cm1 = (us1 / 2.0f) / 29.1f; inch1 = (us1 / 2.0f) * 0.0133f; }
// small gap to avoid cross-talk
delay(60);
// --- Sensor 2 ---
unsigned long us2 = pingUS(TRIG2, ECHO2);
float cm2 = NAN, inch2 = NAN;
if (us2 > 0) { cm2 = (us2 / 2.0f) / 29.1f; inch2 = (us2 / 2.0f) * 0.0133f; }
// Serial debug
if (us1 == 0) Serial.print("S1: no ecaho ");
else { Serial.print("S1: "); Serial.print(cm1,1); Serial.print(" cm "); }
if (us2 == 0) Serial.println("S2: no echo");
else { Serial.print("S2: "); Serial.print(cm2,1); Serial.println(" cm"); }
// Update LCDs
showReading(lcd1, cm1, inch1); // Sensor 1 -> LCD 1
showReading(lcd2, cm2, inch2); // Sensor 2 -> LCD 2
delay(150);
}
