SW-420 Sensor/Code doesn't work--help with vibration sensor

Question

I'm working on a project that uses SW-420 sensors to detect vibrations. I was originally following this tutorial and my code is pasted below. I used a previous post to determine that I should be using the 3.3V pin instead of 5V, so I swapped that. In every tutorial I've seen, both lights on the sensor have worked, but regardless of what GPIO pin I use, the DO-LED doesn't work. (Not sure if that's relevant.)

If I run the code, it will tell me that a vibration has been detected only if I remove and replace the DO cable (using GPIO 27/pin 13) from the pi--but the sensor doesn't register taps/shakes/hard knocks.

Does anybody know what I'm doing wrong? Pic of offending Pi unit

#!/usr/bin/python

import RPi.GPIO as GPIO
import time

channel = 27

GPIO.setmode(GPIO.BCM)
GPIO.setup(channel, GPIO.IN)

def callback(channel):
   if GPIO.input(channel):
      print("Collision Detected!")
   else:
      print("Collision Detected!")

GPIO.add_event_detect(channel, GPIO.BOTH, bouncetime=300)
GPIO.add_event_callback(channel, callback)

while True:
   time.sleep(1)

Answer 1

I guess the pot needs to be adjusted to set the vibration sensitivity you require.

The pot is the square blue component with the cross head screwdriver slots. Typically they have many complete turns (perhaps 10 or more). Turn the pot until you get the desired output on DO.