My wife asked me to design a door bell for our new house.
But wait, I don't want a old classical sound ("ding dong" like we say in french...) ; the bell if often the first contact between visitors and you (or your house), it has to be funny and nice to hear.
Hmm, wait... let me call my neuron...
he a I agree, that could be a funny project, I have some interesting ideas... Let's set down the first requirements :
- The produced sound has to be smooth to ears.
- The visitor must have the choice to call the whole family or to adress one particular member
- The installation must be easy, I don't want to add wires in my walls
- Each ring tone must be easily configurable. I don't want to choose between a few tones, it must be FULLY configurable
- Sound volume must be adjustable
-The WAF* must be as high as possible. Don't even think to add horrible switch buttons and big black box on the walls ! (*WAF : Wife Acceptance Factor).
OK, the first guidelines are drawn. That project "sounds" great, I think next months are gonna be fun... The first key words in my mind to satisfy those requirements are : - Capacitive sensing, At least 5 keys
- Backlit keys
- Wave file playing stored on SD Card
- Audio output on loudspeaker
- Power and communication through existing copper pair - Low power 230Vac supply
Let's cook all this for a few days... See you next time !
Update 2013-11-23 : Why make it simple when we can make it complicated ?
In general, doorbells integrate a good old low voltage transformer, always powered. Even in standby, such transformers have a very bad leakage power, somewhere around a few Watts.
I decided to implement a low power isolated flyback converter. Don't worry, It will onlys use off-the-shelf parts (no transformer winding). With this kind of power supply, we will have less than 0.1W standby current, with a maximum power of 4W, enough to activate the loudspeaker.
That's a bit more work (for me) than a conventionnal 50Hz transformer-based supply, but it's worth it I think.