Overview
The SW-520D module is the simplest motion detector you can wire: a gold-plated cylinder containing two tiny conductive balls that either bridge a pair of contacts or roll away from them as the module tilts. Sit it flat and the circuit is closed; tip it past roughly 15-45 degrees and the balls roll off, the circuit opens, and the D0 pin flips state. No axes, no registers, no calibration — just "upright" or "not upright."
The onboard LM393 comparator turns the raw ball-switch contact into a clean digital output, with a sensitivity trimpot to set the threshold and two indicator LEDs: PWR for supply and a status LED that mirrors D0, so you can watch it trigger before writing a line of code. Because output is a plain logic level, it works identically at 3.3V and 5V and connects to any GPIO with three wires.
Classic jobs: tip-over protection for heaters and machines, tamper/movement alarms on doors, cases, and packages, orientation detection for handheld gadgets, vibration-adjacent sensing on the cheap, and HVAC or appliance interlocks. If you need to know the angle, that's accelerometer territory (ADXL345/MPU6050) — the SW-520D's charm is answering the binary question instantly, for pennies, with zero code overhead.
At a Glance
Sensor
SW-520D ball tilt switch
Output
Digital D0 (LM393)
Trigger Angle
~15-45° from level
Supply Voltage
3.3V - 5V
Indicators
PWR + status LEDs
Pins
VCC, GND, D0
Specifications
| Parameter | Value |
| Sensing Element | SW-520D double-ball tilt switch, gold-plated can |
| Comparator | LM393 dual comparator with trimpot threshold |
| Supply Voltage | 3.3V - 5V DC |
| Current Draw | ~15 mA (mostly the LEDs) |
| Output | Digital, push-pull logic level on D0 |
| Logic Sense | Level (balls bridging) = LOW; tilted = HIGH (typical boards) |
| Trigger Angle | ~15° begins to open, fully open by ~45° |
| Response | Instant; contacts bounce for ~10-50 ms while rolling |
| Indicators | PWR-LED (power), DO-LED (mirrors output) |
| Operating Temperature | -25°C to +80°C |
| Board Size | ~32 x 14 mm, single mounting hole |
Pinout Diagram
Three pins on the right edge: VCC, GND, and D0. The gold cylinder at the corner is the tilt switch itself — mount the board so the cylinder's axis is vertical when your device is "upright." The blue trimpot adjusts the comparator threshold, and the DO-LED lights the moment the output trips, which makes aiming and testing a hands-on affair.
Wiring Guide
Arduino Wiring
| Module Pin | Arduino Pin |
|---|---|
| VCC | 5V |
| GND | GND |
| D0 | D2 |
Tip: Watch the DO-LED while tilting the board by hand — if the LED never changes, turn the blue trimpot until the tilt point sits where you want it before blaming the code.
ESP32 Wiring
| Module Pin | ESP32 Pin | Details |
|---|---|---|
| VCC | 3V3 | Keeps D0 at 3.3V logic |
| GND | GND | |
| D0 | GPIO 27 | Any input-capable GPIO |
Note: Powered from 3V3, the output swings 0-3.3V — directly safe for the ESP32. The module works fine at this voltage; only LED brightness drops slightly.
Raspberry Pi Wiring
| Module Pin | Pi Pin | Details |
|---|---|---|
| VCC | Pin 1 (3.3V) | NOT 5V — protects the GPIO |
| GND | Pin 6 (GND) | |
| D0 | Pin 11 (GPIO 17) |
Warning: Power the module from 3.3V on a Pi. Fed from 5V, D0 idles near 5V — above the Pi's GPIO tolerance.
Raspberry Pi Pico Wiring
| Module Pin | Pico Pin |
|---|---|
| VCC | 3V3(OUT) (pin 36) |
| GND | GND (pin 38) |
| D0 | GP16 (pin 21) |
Code Examples
Each example debounces the ball-switch chatter in software and reports every stable transition — "TILTED!" and "Level again" — the pattern you'd wire into any alarm or safety cutoff.
Arduino
sw520d_arduino.ino
// SW-520D Tilt Switch Module - Arduino Example (debounced)
// D0->D2, VCC->5V, GND->GND
const int tiltPin = 2;
const unsigned long DEBOUNCE_MS = 60;
int stableState;
int lastReading;
unsigned long lastChange = 0;
void setup() {
Serial.begin(9600);
pinMode(tiltPin, INPUT);
stableState = lastReading = digitalRead(tiltPin);
Serial.println("Tilt sensor ready - tip me over!");
}
void loop() {
int reading = digitalRead(tiltPin);
if (reading != lastReading) {
lastChange = millis(); // edge seen - restart timer
lastReading = reading;
}
if (millis() - lastChange > DEBOUNCE_MS && reading != stableState) {
stableState = reading;
if (stableState == HIGH) {
Serial.println("TILTED!");
} else {
Serial.println("Level again");
}
}
}
ESP32 (MicroPython)
sw520d_esp32.py
# SW-520D Tilt Switch Module - ESP32 MicroPython Example
# D0->GPIO 27, VCC->3V3, GND->GND
from machine import Pin
import time
tilt = Pin(27, Pin.IN)
DEBOUNCE_MS = 60
stable = tilt.value()
last_reading = stable
last_change = time.ticks_ms()
print("Tilt sensor ready - tip me over!")
while True:
reading = tilt.value()
if reading != last_reading:
last_change = time.ticks_ms()
last_reading = reading
if (time.ticks_diff(time.ticks_ms(), last_change) > DEBOUNCE_MS
and reading != stable):
stable = reading
print("TILTED!" if stable else "Level again")
time.sleep_ms(5)
Raspberry Pi (Python)
sw520d_rpi.py
#!/usr/bin/env python3
# SW-520D Tilt Switch Module - Raspberry Pi Example
# D0->GPIO17 (pin 11), VCC->3.3V, GND->GND
import RPi.GPIO as GPIO
import time
TILT_PIN = 17
DEBOUNCE_S = 0.06
GPIO.setmode(GPIO.BCM)
GPIO.setup(TILT_PIN, GPIO.IN)
stable = GPIO.input(TILT_PIN)
last_reading = stable
last_change = time.time()
print("Tilt sensor ready - tip me over!")
try:
while True:
reading = GPIO.input(TILT_PIN)
if reading != last_reading:
last_change = time.time()
last_reading = reading
if time.time() - last_change > DEBOUNCE_S and reading != stable:
stable = reading
print("TILTED!" if stable else "Level again")
time.sleep(0.005)
except KeyboardInterrupt:
GPIO.cleanup()
print("Stopped by user")
Raspberry Pi Pico (MicroPython)
sw520d_pico.py
# SW-520D Tilt Switch Module - Pico MicroPython Example
# D0->GP16, VCC->3V3(OUT), GND->GND
# Onboard LED mirrors the tilt state.
from machine import Pin
import time
tilt = Pin(16, Pin.IN)
led = Pin("LED", Pin.OUT)
DEBOUNCE_MS = 60
stable = tilt.value()
last_reading = stable
last_change = time.ticks_ms()
print("Tilt sensor ready - tip me over!")
while True:
reading = tilt.value()
if reading != last_reading:
last_change = time.ticks_ms()
last_reading = reading
if (time.ticks_diff(time.ticks_ms(), last_change) > DEBOUNCE_MS
and reading != stable):
stable = reading
led.value(stable)
print("TILTED!" if stable else "Level again")
time.sleep_ms(5)
Frequently Asked Questions
Which way is HIGH — tilted or level?
On the common LM393 board, level = balls bridging = D0 LOW, and tilted = D0 HIGH — but some batches invert this depending on which comparator input the switch feeds. Spend ten seconds with the serial monitor (or the DO-LED) and note your unit's behavior; if it's backwards from what your code expects, flip the comparison in one line.
The output chatters rapidly when it's near the trigger angle. Is it broken?
No — that's metal balls physically rolling on contacts. At the boundary angle they make and break dozens of times. The debounce logic in every example above (60 ms of stability required) turns that chatter into clean single events. For alarm use, you can also require the tilted state to persist for, say, 500 ms before firing.
What does the blue trimpot actually adjust?
It sets the LM393's reference voltage — effectively how decisively the switch state maps to the output. In practice it fine-tunes where in the ball's roll the output flips and adds a little hysteresis. Set it so the DO-LED changes crisply at the angle you care about. If the LED stays stuck on or off at any angle, the pot is turned to an extreme.
Can it measure the tilt angle?
No — it's a switch, not a sensor: one bit, roughly "more than ~30° off vertical or not." If you need degrees, orientation, or shake intensity, step up to an accelerometer like the ADXL345 or MPU6050 (both in the ShillehTek store, both with manuals). Many projects pair them: the SW-520D as a zero-code hardware interlock, the IMU for measurement.
How is this different from the SW-420 vibration module?
Same board layout, different can. The SW-420 is a spring-based switch that responds to knocks and vibration but re-closes immediately — good for impact detection. The SW-520D is gravity-based: it changes state and stays changed while tilted — good for orientation and tip-over. Rule of thumb: transient events → SW-420; persistent orientation → SW-520D.
Can I trigger an interrupt instead of polling?
Yes — D0 drives GPIO interrupts on every platform (attachInterrupt on Arduino, Pin.irq in MicroPython, GPIO.add_event_detect on the Pi). Keep the debounce though: fire the ISR on change, then validate the state after ~60 ms in the main loop. For battery projects, an interrupt from this module is an excellent wake-from-sleep source since it draws no standby GPIO current.
Does mounting orientation matter?
Completely — gravity is the sensing mechanism. Mount the board so the gold cylinder stands vertical (pins down) in the "normal" orientation of your device; tilting the cylinder toward horizontal is what opens the contacts. Avoid mounting it where constant strong vibration will rattle the balls (conveyor frames, engines) — there the chatter never settles and an accelerometer serves better.