KY-031 Knock Sensor Module
The KY-031 is a knock sensor module that detects physical impacts or vibrations. Upon detecting a knock, it outputs a digital signal, making it suitable for applications like interactive projects, security systems, or any setup requiring tap detection.
KY-031 pinout
The KY-031 is a 3-pin knock/vibration sensor module:
| Pin | Type | Description | Notes |
|---|---|---|---|
| - | Power | Ground connection | |
| middle | Power | Power supply | 3.3V or 5V |
| S | Communication | Signal output | HIGH pulse on knock detection |
Interface: Digital vibration sensor
Sensor: Vibration switch (spring-based contact mechanism)
Signal: Outputs HIGH pulse when knock/vibration detected
Power: 3.3V to 5V operation
Sensitivity: Detects sudden impacts and vibrations
Applications: Knock detection, tap interfaces, vibration alarms, security triggers
Wiring the KY-031 to ESP32
To interface the KY-031 with an ESP32 for knock detection:
| KY-031 pin | ESP32 pin | Purpose |
|---|---|---|
| - | GND | Ground |
| middle | 3.3V or 5V | Power supply |
| S | GPIO16 | Digital input (any GPIO) |
Detection: Momentary HIGH pulse when knock/vibration occurs
Debouncing: Software debouncing recommended to filter multiple triggers
Pull-down: May require pull-down resistor for stable LOW state
Sensitivity: Varies with impact force - stronger knocks produce more reliable triggers
Mounting: Secure mounting improves sensitivity and consistency
False Triggers: May respond to nearby vibrations or bumps
LED Indicator: Some versions include LED that lights on detection
KY-031 code examples
int knock = 16; // KY-031 signal pin (GPIO16, matches the wiring above)
int value;
void setup() {
pinMode(knock, INPUT_PULLUP); // Spring switch closes to GND on a knock
Serial.begin(115200);
Serial.println("KY-031 Knock test");
}
void loop() {
value = digitalRead(knock);
if (value == LOW) { // If knock detected
Serial.println("Knock recognized");
delay(200); // Delay to avoid multiple detections
}
}This Arduino code initializes the sensor input pin and serial communication. In the loop, it continuously reads the sensor value and prints "Knock recognized" to the serial monitor when a knock is detected.
#include <stdio.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "driver/gpio.h"
#define KNOCK_SENSOR_PIN GPIO_NUM_16
static void IRAM_ATTR knock_isr_handler(void* arg);
void app_main(void) {
gpio_config_t io_conf = {
.intr_type = GPIO_INTR_NEGEDGE, // Interrupt on falling edge
.mode = GPIO_MODE_INPUT,
.pin_bit_mask = (1ULL << KNOCK_SENSOR_PIN),
.pull_up_en = GPIO_PULLUP_ENABLE
};
gpio_config(&io_conf);
gpio_install_isr_service(0);
gpio_isr_handler_add(KNOCK_SENSOR_PIN, knock_isr_handler, NULL);
printf("KY-031 Knock Sensor Test\n");
while (1) {
vTaskDelay(pdMS_TO_TICKS(1000));
}
}
static void IRAM_ATTR knock_isr_handler(void* arg) {
printf("Knock detected!\n");
}This ESP-IDF code configures GPIO16 as an input with an interrupt on the falling edge. When a knock is detected, an interrupt service routine (ISR) is triggered, printing "Knock detected!" to the console.
binary_sensor:
- platform: gpio
pin:
number: GPIO16
mode: INPUT_PULLUP
name: "KY-031 Knock Sensor"
filters:
- delayed_off: 200msThis ESPHome configuration sets up a binary sensor for the KY-031 knock sensor connected to GPIO16. It uses a delayed_off filter to prevent multiple detections from a single knock.
[env:esp32]
platform = espressif32
board = esp32dev
framework = arduino#include <Arduino.h>
#define KNOCK_SENSOR_PIN 16
void setup() {
pinMode(KNOCK_SENSOR_PIN, INPUT_PULLUP);
Serial.begin(115200);
Serial.println("KY-031 Knock Sensor Test");
}
void loop() {
if (digitalRead(KNOCK_SENSOR_PIN) == LOW) {
Serial.println("Knock detected!");
delay(200); // Debounce delay
}
delay(50);
}This PlatformIO code sets up GPIO16 as an input with a pull-up resistor for the KY-031 knock sensor. When a knock is detected, a message is printed to the serial monitor, and a debounce delay of 200ms prevents false triggers.
import machine
import time
KNOCK_SENSOR_PIN = machine.Pin(16, machine.Pin.IN, machine.Pin.PULL_UP)
while True:
if KNOCK_SENSOR_PIN.value() == 0:
print("Knock detected!")
time.sleep(0.2) # Debounce delay
time.sleep(0.05)This MicroPython script configures GPIO16 as an input with a pull-up resistor for the KY-031 knock sensor. It continuously checks for knocks and prints a message when one is detected, with a debounce delay to prevent multiple detections from a single event.
KY-031 specifications
About the KY-031
The KY-031 uses the same kind of spring-in-a-can mechanism as the KY-002 vibration switch - a conductive spring inside a metal shell that taps the wall and briefly closes the circuit on impact - but sellers and hobbyist writeups consistently describe it as the less sensitive of the two, tuned to need a real knock rather than a light bump or vibration. There’s no comparator or potentiometer on the board to confirm that difference electrically, so treat it as a difference in the switch’s internal spring tension rather than anything adjustable from outside.
Like any mechanical contact, the connection bounces: a single knock on the enclosure typically produces several rapid HIGH/LOW transitions within milliseconds rather than one clean edge, so debounce it in software (a short delay or an edge-count window) the same way you would a pushbutton. It runs on the same 3.3-5V logic as the rest of the ESP32’s GPIOs, and since it only reports “impact happened” with no measure of force or direction, it’s a trigger for taps and hits, not a stand-in for an accelerometer.
KY-031 troubleshooting
No Response from Sensor
›
Issue: The sensor does not detect knocks or vibrations.
Solutions:
- Verify all wiring connections are secure and correctly placed.
- Ensure the sensor is receiving the appropriate voltage (3.3V or 5V).
- Test the sensor with a known good microcontroller pin to rule out pin issues.
False Triggering
›
Issue: The sensor outputs signals without any physical impact.
Solutions:
- Check for external vibrations or noise that might be causing false triggers.
- Implement software debouncing to filter out spurious signals.
- Ensure the sensor is mounted securely to prevent unintended movements.
Where to buy the KY-031
Resources
Similar sensors
