“Our freezer is in a utility room which is isolated from our living space. Occasionally the freezer door doesnt shut properly and the alarm goes off. The problem is that we cant hear it if we are in our living space. How do we get a message that the freezer door is open? This is a common issue, we have devices in our homes that talk to us, but what happens if we can’t hear them for whatever reason. I started this as a bit of fun, but it may be of use in a more serious application.
There are 2 parts to this problem, we need a method to detect the alarm has gone off and a method to relay this fact to our living space. The design I settled on was to use a Raspberry Pi to listen for the freezer alarm going off, and then to send an audible alarm message to my domestic radio which is uPNP enabled. Universal Plug and Play(UpnP) is a standard for discovering and interacting with services offered by various devices on a network, including media servers and players, though I dont think freezers were envisaged when the standard was developed. The warning message was made loud and irritating and repeats endlessly until the radio is turned off.
I chose to detect the alarm with a Raspberry Pi Zero W and Seeed ReSpeaker 2-Mics Pi HAT The Raspberry PI Zero is a low cost version of the Raspberry Pi and the W option has builtin WiFi, while the Seeed Pi HAT retails for less than $10, has built-in LEDs and a User Button. Pi HAT are extension cards that plug directly onto the Raspberry Pi making a very simple assembly procedure. Any Pi version would be more than capable for the job, and the microphone chosen can be substituted, though I made use of the built-in LEDs in this build.
It is easy to check if a radio or TV would work for you. It will more likely be described as “DLNA enabled” or similar. This uses uPNP to communicate. On a Windows PC, select an mp3 file and Cast to Device. If your device shows up and you can play the file, then you are good to go.
I split the software into 2 python scripts, checkFreezer.py to check whether a freezer alert has been triggered and raiseAlarm.py to raise the alarm. These scripts could be developed and tested separately and can easily be adapted or substituted for different microphones alarm raising methods.
Raspberry PI Zero W
Seeed ReSpeaker 2-Mics Pi HAT
uPNP enabled radio”