ESP32 C3 Super Mini - Motion Sensor - Relay
This ESP32 C3 Super Mini motion sensor relay tutorial shows you how to switch a device on automatically when someone moves nearby. The ESP32 C3 Super Mini turns the relay on when the HC-SR501 detects motion, and turns it off when the motion stops.
In this tutorial, you'll learn:
- How to wire an HC-SR501 motion sensor and a relay to ESP32 C3 Super Mini
- How to set the sensor adjusters before you start
- How to program ESP32 C3 Super Mini to control a relay from motion
- How to read motion events in the Serial Monitor
- How to extend the project to a LED strip, siren, light bulb or actuator
Hardware Preparation
Or you can buy the following kits:
| 1 | × | DIYables Sensor Kit (18 sensors/displays) |
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Additionally, some of these links are for products from our own brand, DIYables .
Additionally, some of these links are for products from our own brand, DIYables .
Overview of Relay and Motion Sensor
A relay is a switch your code can control, and the HC-SR501 is a sensor that detects moving people and animals.
- Relay: Switches a higher-power device on and off from one output pin
- HC-SR501 Motion Sensor: Sends HIGH when it detects motion and LOW when it does not
- Relay guide: See the ESP32 C3 Super Mini - Relay tutorial for the pinout, how it works and more
- Motion sensor guide: See the ESP32 C3 Super Mini - Motion Sensor tutorial for the pinout, how it works and more
Wiring Diagram
Connect the motion sensor and the relay to your ESP32 C3 Super Mini as shown below.
- Note: Both the HC-SR501 and the relay use the 5V pin for power
- Note: The OUTPUT pin of the HC-SR501 gives about 3.3V, so it is safe for GPIO5
- Note: Turn off all power before you change any wire
This image is created using Fritzing. Click to enlarge image
| HC-SR501 Pin | ESP32 C3 Super Mini Pin |
|---|---|
| VCC | 5V |
| GND | GND |
| OUTPUT | GPIO5 |
| Relay Pin | ESP32 C3 Super Mini Pin |
|---|---|
| DC+ | 5V |
| DC- | GND |
| IN | GPIO6 |
Initial Setting
Set the HC-SR501 adjusters before you run the code.
| Setting | Configuration |
|---|---|
| Detection Range Adjuster | Fully screw it in the clockwise direction. |
| Time Delay Adjuster | Fully screw it in the anti-clockwise direction. |
| Repeat Trigger Selector | Put jumper like the below image. |
ESP32 C3 Super Mini Code
This code turns the relay on and off based on the motion sensor.
What This Code Does:
- Reads the HC-SR501 motion sensor on GPIO5
- Detects when motion starts (LOW to HIGH)
- Turns the relay on with GPIO6 when motion starts
- Detects when motion stops (HIGH to LOW)
- Turns the relay off and prints each event to the Serial Monitor
/*
* This ESP32 C3 Super Mini code was developed by newbiely.com
*
* This ESP32 C3 Super Mini code is made available for public use without any restriction
*
* For comprehensive instructions and wiring diagrams, please visit:
* https://newbiely.com/tutorials/esp32-c3/esp32-c3-super-mini-motion-sensor-relay
*/
#define MOTION_SENSOR_PIN 5 // The ESP32 C3 SuperMini pin GPIO5 connected to the OUTPUT pin of motion sensor
#define RELAY_PIN 6 // The ESP32 C3 SuperMini pin GPIO6 connected to Relay's pin
int motionStateCurrent = LOW; // current state of motion sensor's pin
int motionStatePrevious = LOW; // previous state of motion sensor's pin
void setup() {
Serial.begin(115200); // initialize serial
pinMode(MOTION_SENSOR_PIN, INPUT); // set ESP32 C3 SuperMini pin to input mode
pinMode(RELAY_PIN, OUTPUT); // set ESP32 C3 SuperMini pin to output mode
}
void loop() {
motionStatePrevious = motionStateCurrent; // store old state
motionStateCurrent = digitalRead(MOTION_SENSOR_PIN); // read new state
if (motionStatePrevious == LOW && motionStateCurrent == HIGH) { // pin state change: LOW -> HIGH
Serial.println("Motion detected!, turns relay ON");
digitalWrite(RELAY_PIN, HIGH); // turn on
} else if (motionStatePrevious == HIGH && motionStateCurrent == LOW) { // pin state change: HIGH -> LOW
Serial.println("Motion stopped!, turns relay OFF");
digitalWrite(RELAY_PIN, LOW); // turn off
}
}
Detailed Instructions
- New to ESP32 C3 Super Mini? Complete our Getting Started with ESP32 C3 Super Mini tutorial first to set up your development environment.
- Wire It Up: Do the wiring as shown in the image above.
- Connect the Board: Connect the ESP32 C3 Super Mini to your PC with a USB Type-C cable.
- Open the IDE: Open Arduino IDE on your PC.
- Select the Board: Make sure ESP32 C3 Super Mini is selected in Tools > Board.
- Select the Port: Choose the right COM port in Tools > Port.
- Paste the Code: Copy the code above and paste it into Arduino IDE.
- Upload: Click the Upload button on Arduino IDE to compile and upload the code.
- Open Serial Monitor: Set the baud rate to 115200.
- Test It: Move your hand in front of the sensor.
- Check the Result: See the relay change state and read the message in the Serial Monitor.
- Pro Tip: If the Serial Monitor stays empty, set Tools > USB CDC On Boot to Enabled and upload again.
Line-by-line Code Explanation
The ESP32 C3 Super Mini code above has a comment on each important line.
- Read the comments: They explain what each line does, line by line.
Serial Monitor Output
When you move in front of the sensor and then stop, you will see this:
8
Serial.println("Hello World!");
Message (Enter to send message to 'ESP32C3 Dev Module' on 'COM15')
New Line
9600 baud
Motion detected!, turns relay ON
Motion stopped!, turns relay OFF
Motion detected!, turns relay ON
Motion stopped!, turns relay OFF
Relay vs MOSFET Module
A relay is not the only way to switch a device. If your device runs on DC power, such as a 12V LED strip, a 12V solenoid lock or a 12V fan, a MOSFET module can do the same job.
| Relay | MOSFET Module | |
|---|---|---|
| What it can do | turn the device on or off | turn the device on or off, and set its power (PWM) |
| Noise when switching | a click every time | no sound |
| How fast it switches | slow, a few milliseconds | very fast |
| Life | the contacts wear out after many switches | nothing moves, so it lasts long |
| Type of power | AC or DC | DC only |
| Device power supply | any voltage the relay is rated for | about 6V or more |
| Isolation from the ESP32 C3 Super Mini | yes, between coil and contacts | yes, by the PC817 optocoupler |
| Good for | AC devices, or a simple ON/OFF | DC devices, or dimming and speed control |
Both the relay and the MOSFET module turn on when the ESP32 C3 Super Mini pin is HIGH. The pin gives only 3.3V, but that is enough: the LED of the optocoupler on the module needs just a few milliamps. So for a simple ON/OFF, the code above stays the same and only the wiring changes.
- AC mains devices: Always use the relay.
- Learn more: See the ESP32 C3 Super Mini - MOSFET Module tutorial for the pinout, wiring, PWM code and safety tips.
Project Ideas
You can connect many devices to this ESP32 C3 Super Mini motion sensor relay project.
- Automatic Light: Turn on a LED strip or light bulb when someone walks in
- Intruder Siren: Sound a 12V buzzer or siren when motion is detected
- Warning Light: Flash a bright warning light near a door or gate
- Smart Fan: Run a 12V cooling fan only when someone is in the room
- Automatic Lock: Trigger a solenoid lock when someone comes close
- Moving Display: Start an actuator when a visitor walks past
Challenge Yourself
Try these ideas to grow your ESP32 C3 Super Mini skills.
- Easy: Change the Serial Monitor messages to your own text
- Easy: Add an LED on GPIO3 that follows the relay state
- Medium: Keep the relay on for 30 seconds after the motion stops
- Medium: Count how many times motion is detected and print the number
- Advanced: Add a button that turns the motion control on and off
- Advanced: Replace the relay with a MOSFET module and fade the device on with PWM