10€ remote doorbell
To solve this problem I found a 10€ remote bell that sits in the kitchen and rings whenever somebody rings our door bell.
Initially I wanted a fancy WIFI based solution based on an ESP32 that would call me via SIP... But in the end this simple solution is "good enough" and has the benefit of zero maintenance.
My solution is based on a kinetic wireless doorbell (batterielose Funktürklingel) that has two components: A ringer that sits in a power socket and a transmitter without batteries. The "without batteries" part is really important as it allows a direct connection and integration of the transceiver into the door phone. As it happens, what I needed was available for 10€ at a local supermarket, but you can easily find this type of doorbell in online stores as well.
The ringer contains a little generator and a wireless transceiver. The generator is triggered by pushing the bell button and it generates enough energy for the transceiver to send a signal to the ringer.
For our little project we only need the transceiver, which is a small PCB. After dismantling the ringer I also had to remove (unsolder) the generator - the only difficult part here. The generator looks like this:
Flipping the plastic handle up and down drives a magnet through the coil which generates a short spike of electricity. A spring returns the handle to its original position in the ringer.
Luckily the power input of the transceiver can handle this directly so that there is no need for any additional circuitry.
After puzzling for a long time about how to solve our doorbell problem, it is amazing how finding the right tool made solving the problem very very simple.
When I put it together there was only one caveat: The doorphone will trigger the 5V switch output only when the phone handset is on hook, e.g. hanging properly on the phone. Without that the output stays dead and I first thought that I broke something. Eventually I put it all together and then it started to work. The RITTO Rufanschaltrelais manual also explains this confusing behavior.
The result is a totally invisible wireless doorbell extension for just 10€.
While researching the topic the following websites helped me a lot:
I hope you find this little hack useful.