science club |
Building an outdoor door chime
In summer we are often out in the backyard and we would frequently
not hear the door bell. I decided therefore to build an outdoor
recordable chime based on the ISD1820 analog sound recording module.
The outdoor chime does not just produce a short ding-dong that is easily overheard but plays for
several seconds and allows you to listen-up carefully if you thought that you
heard something. This way you have a reliable door bell sound that is not
too loud and still easily recognized. I recored the sounds of Big Ben on it ( http://www.parliament.uk/about/living-heritage/building/palace/big-ben/anniversary-year/downloads/ ).
How to add a second bell?
I do not believe in wireless door bell systems. They are simply not reliable.
Not only radio interference may cause them to fail but as well cold weather
since the push button at the door is battery powered.
This article is therefore about wired door bell installations. The best way
to add a second door chime in a wired installation is a relay. This way you don't have to worry
about the different voltages that the systems might use. You simply
insert a relay with 2 independent contact pairs (DPDT):
Using a relay to control 2 door bells with one button (click to view as pdf)
Here is a photo of this relay installation in the basement. I used a small 9V DC power
supply for the relay and this power supply is as well used to supply
power to the outdoor chime.
All the wires come together in the basement and this is where I installed
the relay (small white box)
Building a recordable door chime
The ISD1820 is a made in china analog sound recording chip and you
can buy small ready to use modules with that chip on ebay. Ask if
the module comes with a circuit diagram before you buy one. I used
such a module to record and play the sound and I added a small
amplifier stage to make it louder.
The ISD1820 module requires 5V DC but 5V is not enough for a good amplifier stage. I used 9V to power the amplifier and then a small 78L05 to provide 5V to the ISD1820.
The ISD1820 module with additional amplifier stage. (click on the image to view it as pdf)
This makes basically an independent door chime on which you can record about 10sec of sound and then play it back as often as you want. CONN2 is the connection to the relay contacts.
The second door chime installed outside on the wall. The loudspeaker opening is towards the bottom and thus protected from direct rain. I used a speaker with a plastic membrane (mylar membrane).
Copyright © 2004-2018 Guido Socher