The sys admin's daily grind: Charly's doorbell Pi
Ring, Ring
When Charly puts on his headphones at home, he often fails to hear the doorbell. So, he dreamed up a solution with a Raspberry Pi Zero, a noise detector, and a power outlet with a LAN connection.
Sometimes I sit in my home office using a headset, listening to some good old electric guitar music or taking part in a teleconference – which is naturally slightly less invigorating. As a consequence of my acoustic escapism, I tend not to hear anyone who rings the doorbell.
To restore my social presence, I opted for the smallest version of the Raspberry Pi, the Zero. The Pi needs to detect the bell circuit closing and output a visual alert. In Germany, doorbells use 8 to 12V alternating current. You could convert this to DC and tune it down to a Pi-compatible voltage, but this would involve a mess of wire in the doorbell housing.
So, I went for a noise sensor. These things are very simply made, need a supply voltage of 5V, and send a signal via the output pin when they pick up a noise [1]. A blue rotary potentiometer lets me set the noise level. The sensor and the Raspberry Pi both fit into the doorbell housing (Figure 1).

Because of its proximity to the acoustic event, I can set the sensor's switching threshold to a fairly high level – it will not be tripped by the kids shouting or the dog going mad in the hallway.
Lights and Tweets
The small Python program from Listing 1 evaluates the signal in an infinite loop. The GPIO Zero library [2], which I used here, might not support noise sensors, but its Button()
function is all I need to evaluate the sensor's short voltage pulse. Luckily, it includes a debounce feature: bounce_time=2
summarizes all the signals the Raspberry detects within two seconds.
Listing 1
Doorbell Script
01 #!/usr/bin/env python3 02 from gpiozero import Button 03 from signal import pause 04 import os 05 06 def bell_rang (): 07 os.system("/usr/local/shellscripts/bell.sh") 08 09 button = Button(21, bounce_time=2) 10 button.when_pressed = bell_rang 11 pause()
When the delivery man rings the bell now, the script bell.sh
launches, which actuates a power outlet connected to my LAN, which switches on a lamp in my office. At the same time, the script sends a tweet on Twitter. I know you can buy wireless doorbells down at the hardware store, but the doorbell Pi is more my style.
Charly Kühnast
Charly Kühnast is a Unix operating system administrator at the Data Center in Moers, Germany. His tasks include firewall and DMZ security and availability. He divides his leisure time into hot, wet, and eastern sectors, where he enjoys cooking, freshwater aquariums, and learning Japanese, respectively.
Infos
- Source for noise sensor: http://www.amazon.de/gp/product/B00N1TSM7K
- GPIO Zero: http://gpiozero.readthedocs.org
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Direct Download
Read full article as PDF:
Price $2.95
News
-
Titan Linux is a New KDE Linux Based on Debian Stable
Titan Linux is a new Debian-based Linux distribution that features the KDE Plasma desktop with a focus on usability and performance.
-
Danielle Foré Has an Update for elementary OS 7
Now that Ubuntu 22.04 has been released, the team behind elementary OS is preparing for the upcoming 7.0 release.
-
Linux New Media Launches Open Source JobHub
New job website focuses on connecting technical and non-technical professionals with organizations in open source.
-
Ubuntu Cinnamon 22.04 Now Available
Ubuntu Cinnamon 22.04 has been released with all the additions from upstream as well as other features and improvements.
-
Pop!_OS 22.04 Has Officially Been Released
From the makers of some of the finest Linux-powered desktop and laptop computers on the market comes the latest version of their Ubuntu-based distribution, Pop!_OS 22.04.
-
Star Labs Unveils a New Small Format Linux PC
The Byte Mk I is an AMD-powered mini Linux PC with Coreboot support and plenty of power.
-
MX Linux Verison 21.1 “Wildflower” Now Available
The latest release of the systemd-less MX Linux is now ready for public consumption.
-
Microsoft Expands Their Windows Subsystem for Linux Offerings With AlmaLinux
Anyone who works with Windows Subsystem for Linux (WSL) will now find a new addition to the available distributions, one that’s become the front-runner replacement for CentOS.
-
Debian 11.3 Released wIth Numerous Bug and Security Fixes
The latest point release for Debian Bullseye is now available with some very important updates.
-
The First Alpha of Asahi Linux is Available
Asahi Linux is the first distribution to fully support Apple Silicon and is now available for testing.