Circuit Diagram:
Ultrasonic Relay Toggle System
This project implements a touchless light control system using an Ultrasonic sensor, an OLED display, and a Relay module. The system toggles a light (represented by the relay) ON or OFF whenever an object is detected within a specific range.
🔗 Wokwi Simulation
You can view and run the simulation here:
https://wokwi.com/projects/461731925906866177
🛠 Features
- Touchless Control: Uses ultrasonic waves to detect proximity.
- Toggle Logic: Prevents flickering; one detection turns it ON, the next detection turns it OFF.
- Visual Feedback: Real-time status updates on a 128x64 I2C OLED display.
- Industrial Interface: Relay output to control high-voltage appliances (simulated).
📟 Component Pinout
| Component | Pin Name | Arduino/MCU Pin |
|---|---|---|
| Ultrasonic Sensor | Trig | Pin 9 |
| Ultrasonic Sensor | Echo | Pin 10 |
| Relay Module | Signal | Pin 12 |
| OLED Display | SDA | A4 (or SDA) |
| OLED Display | SCL | A5 (or SCL) |
🧠 Logic Explanation
1. Distance Calculation
The HC-SR04 sensor measures return time and converts it to cm:
Distance = (Duration * 0.034) / 2
2. State-Change Detection
The code checks for the moment an object appears (Edge Triggering) to prevent constant toggling while someone stands in front of the sensor.
3. Toggle Mechanism
The relayState flips every time a detection occurs, switching the lights between ON and OFF status.
DIAGRAM.JSON - PROJECT CONFIGURATION
{
"version": 1,
"author": "Computer work",
"editor": "wokwi",
"parts": [
{ "type": "wokwi-arduino-nano", "id": "nano", "top": 52.8, "left": -48.5, "attrs": {} },
{
"type": "wokwi-hc-sr04",
"id": "ultrasonic1",
"top": -123.3,
"left": -4.1,
"attrs": { "distance": "2" }
},
{ "type": "wokwi-relay-module", "id": "relay1", "top": 163.4, "left": 9.6, "attrs": {} },
{
"type": "board-ssd1306",
"id": "oled1",
"top": 41.54,
"left": 221.03,
"attrs": { "i2cAddress": "0x3c" }
},
{
"type": "wokwi-led",
"id": "led1",
"top": 140.4,
"left": 195.8,
"attrs": { "color": "cyan" }
},
{
"type": "wokwi-led",
"id": "led2",
"top": 140.4,
"left": 224.6,
"attrs": { "color": "magenta" }
},
{
"type": "wokwi-led",
"id": "led3",
"top": 140.4,
"left": 253.4,
"attrs": { "color": "blue" }
},
{
"type": "wokwi-led",
"id": "led4",
"top": 140.4,
"left": 282.2,
"attrs": { "color": "white" }
},
{
"type": "wokwi-text",
"id": "text1",
"top": -163.2,
"left": -96,
"attrs": { "text": "Ultrasonic Sensor For Person Detection in this Project" }
},
{
"type": "wokwi-text",
"id": "text2",
"top": 211.2,
"left": 211.2,
"attrs": { "text": "Room Lights" }
},
{
"type": "wokwi-text",
"id": "text3",
"top": 278.4,
"left": 0,
"attrs": { "text": "Relay for Switching" }
},
{
"type": "wokwi-text",
"id": "text4",
"top": 9.6,
"left": 297.6,
"attrs": { "text": "Display" }
}
],
"connections": [
[ "ultrasonic1:GND", "nano:GND.2", "black", [ "v19.2", "h-20.4" ] ],
[ "oled1:GND", "nano:GND.1", "black", [ "v-19.2", "h-67.2", "v105.6", "h-57.6" ] ],
[ "relay1:GND", "nano:GND.1", "black", [ "h-28.8", "v-38.8", "h115.2" ] ],
[ "relay1:VCC", "nano:5V", "red", [ "h-19.2", "v-38.4", "h86.4" ] ],
[ "ultrasonic1:VCC", "nano:5V", "red", [ "v28.8", "h-153.6", "v144", "h163.2" ] ],
[ "oled1:VCC", "nano:5V", "red", [ "v-28.8", "h-95.85", "v124.8", "h-96" ] ],
[ "ultrasonic1:TRIG", "nano:9", "green", [ "v19.2", "h-77.2" ] ],
[ "ultrasonic1:ECHO", "nano:10", "green", [ "v9.6", "h-96.8", "v76.8" ] ],
[ "relay1:IN", "nano:12", "green", [ "h-76.8", "v-192.2", "h38.4" ] ],
[
"oled1:SDA",
"nano:A4",
"green",
[ "v-48", "h67.27", "v240", "h-393.6", "v-105.6", "h76.8" ]
],
[
"oled1:SCL",
"nano:A5",
"green",
[ "v-57.6", "h86.7", "v259.2", "h-412.8", "v-124.8", "h96", "v-19.2" ]
],
[ "led1:C", "led2:C", "black", [ "v19.2", "h29.2" ] ],
[ "led2:C", "led3:C", "black", [ "v19.2", "h29.2" ] ],
[ "led3:C", "led4:C", "black", [ "v19.2", "h29.2" ] ],
[ "led1:C", "nano:GND.2", "black", [ "v19.2", "h-47.6", "v-172.8", "h-86.4" ] ],
[ "nano:3.3V", "relay1:COM", "red", [ "v38.4", "h-9.6", "v115.2", "h182.4", "v-76.8" ] ],
[ "relay1:NO", "led1:A", "green", [ "h20.4", "v7.8", "h76.8" ] ],
[ "led1:A", "led2:A", "green", [ "v28.8", "h9.6" ] ],
[ "led2:A", "led3:A", "green", [ "v28.8", "h28.8" ] ],
[ "led3:A", "led4:A", "green", [ "v28.8", "h28.8" ] ]
],
"dependencies": {}
}
Arduino Code
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
// OLED Configuration
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);
// Pin Definitions
const int trigPin = 9;
const int echoPin = 10;
const int relayPin = 12;
// Variables
bool relayState = false; // Current state of the relay
bool objectPresent = false; // Whether an object is currently in range
bool lastObjectPresent = false; // Previous detection state
int threshold = 350; // Detection distance in cm
void setup() {
pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);
pinMode(relayPin, OUTPUT);
digitalWrite(relayPin, LOW); // Start with lights off
if(!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
for(;;); // Don't proceed if OLED fails
}
updateDisplay("System Ready");
delay(1000);
updateDisplay("Lights: OFF");
}
void loop() {
long duration;
int distance;
// Trigger the ultrasonic sensor
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);
duration = pulseIn(echoPin, HIGH);
distance = duration * 0.034 / 2;
// Check if an object is within the threshold
if (distance > 0 && distance < threshold) {
objectPresent = true;
} else {
objectPresent = false;
}
// Toggle Logic: Trigger only when an object first appears (State Change)
if (objectPresent == true && lastObjectPresent == false) {
relayState = !relayState; // Flip the state
if (relayState) {
digitalWrite(relayPin, HIGH);
updateDisplay("Lights: ON");
} else {
digitalWrite(relayPin, LOW);
updateDisplay("Lights: OFF");
}
delay(5000); // Small debounce delay to prevent double-triggering
}
lastObjectPresent = objectPresent; // Save the state for the next loop
delay(50);
}
void updateDisplay(String message) {
display.clearDisplay();
display.setTextSize(2);
display.setTextColor(WHITE);
display.setCursor(0, 20);
display.println(message);
display.display();
}
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