Pi Zero Button pressed detected incorrectly

Question

^{simulate this circuit – Schematic created using CircuitLab}

I have a script that sends me a firebase notification when the doorbell is pressed. It was working fine when it was on the breadboard. After connecting the project to the doorbell it was randomly sending notifications.

So i've stripped the project back and I think it's something on the Pi as I currently just have a wire on GPIO18 and Ground so i can simulate a button press. However the button press is triggered by simply touching the wire or when another wire is attached to the GPIO pin.

I've got my script below:

from os import system, name
from pyfcm import FCMNotification
import json
from firebase import firebase
import RPi.GPIO as GPIO
import time
from datetime import datetime
import calendar


buttonPin = 18
chimePin = 22

GPIO.setmode(GPIO.BCM)

GPIO.setup(buttonPin, GPIO.IN, pull_up_down=GPIO.PUD_UP)
GPIO.setup(chimePin, GPIO.OUT)

push_service = FCMNotification(api_key="MY_API_KEY")

def send_fcm_messages(reg_ids, body):
        try:
                results = push_service.notify_multiple_devices(registration_ids=reg_ids, message_title='Ding Dong', message_body=body)
        except pyfcm.errors.FCMServerError as e:
                 time.sleep(0.5)
                results = send_fcm_messages(reg_ids, body)
         i = 0
         for k,v in results.items():
                if k == "failure":
                        if v == 1:
                                print("remove device")
                                f.delete('/devices', reg_ids[i])
        i += 1
        return results

while True:
    input_state = GPIO.input(buttonPin)
    if input_state == False:
        GPIO.output(chimePin, GPIO.HIGH)
        time.sleep(0.1)
        GPIO.output(chimePin, GPIO.LOW)
        system('clear')
        d = datetime.utcnow()
        unixtime = calendar.timegm(d.utctimetuple())
        url = 'https://my-firebase-url'
        f = firebase.FirebaseApplication(url, None)
        # your variables are already assigned before this
        data = str(unixtime)
        f.put("/dings/", data, data)
        dateTimeStr = datetime.fromtimestamp(unixtime).strftime('%a %d/%m/%Y %H:%M:%S')
        devices = f.get('/devices', None);
        reg_ids = list()
        for k,v in devices.items():
                reg_ids.append(k)
        result = send_fcm_messages(reg_ids, dateTimeStr)
        print('Doorbell Pressed ' + dateTimeStr)

Door Chime Circuit:

Answer 1

The most likely reason is that the internal pull-up on the button GPIO is not strong enough to counteract the aerial effect of the connected wire.

The internal pulls are about 50k ohm. A wire acts like an aerial and radio pulses can generate a train of pulses. Try using a 10k ohm external resistor between the button GPIO and the 3V3 rail.

Answer 2

I'm not sure your circuit is right. Is the collector of the transistor really connected to ground? If so I don't see how it ever turns on. Not that it would cause the problem you have, but I think there may be some issue with power supplies and grounding. Can you be more specific about how the chime and USB power supplies are wired? And how the chime works - or a link to the manufacturer's data sheet.

Answer 3

What happens id you remove everything except the pusbutton and the wires from it ground and the gpio pin? Do you still have a problem with false alerts? If so, then it seems the wiring IS picking up RF interference. A small capacitor (100nF) wired across the pushbutton ought to kill that. Once have you solved this simple arrangement you can move on to the chime circuit.