Vibration sensor - What I am doing wrong?

Question

I am trying to use a vibration sensor with my Raspberry Pi. The wiring looks like this:

3.3V -> VIBRATION SENSOR -> LED (Grounded) -> GPIO6

Whenever I touch the vibration sensor, the led goes on.

I wrote the following script:

from time import sleep
import RPi.GPIO as GPIO

GPIO.setmode(GPIO.BCM)
GPIO.setup(6, GPIO.IN)
sleep(0.1)

while True:
    result = GPIO.input(6)
    if result == 1:
        print("Vibrated")

The problem is that I am getting tons of vibration even when nothing touches the sensor (the LED is off).

What I am doing wrong here? I would expect the GPIO to report high only when a 3.3V current flows through the wire.

Answer 1

What you are likely seeing is the result of your SENSOR->LED->GPIO6 line being in a "floating" state - it is not part of an active circuit and hence the voltage on the line is fluctuating.

You will need to enable the pull-down resistor on GPIO6 by replacing

GPIO.setup(6, GPIO.IN)

with

GPIO.setup(6, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)

A pulldown resistor basically ensures that if the line is floating, it will get connected to Ground (0V) and always read LOW. Similarly, using a pullup resistor ensures that if the line is floating, it will get connected to 3V3 and always read HIGH. The value of the resistor is high enough (in the order of 50kOhm) to effectively block the path to 0V/3V3 once the line is connected to a circuit, current is flowing and the line no longer floats.