Musical doorbells... tacky aren't they?
... but then I never said I had any taste!

I fiancée asked me wouldn't it be cool if we had a doorbell that played the theme from the great escape... This is was the challenge... I couldn't find a commercially available doorbell that played this tune, so I decided I would have to build my own.

Tacky beepy tunes are all around us these days with the advent of the mobile ring tone. So I hatched a plan to use the wealth of tunes written in "mobile phone" format to form the basis of my doorbell.

HARDWARE

PIC16F84 - 8bit microprocessor, very self contained and requires few external components.
Simple transistor amplifier to drive a speaker.

The circuit is very simple the PIC uP held in SLEEP mode until the doorbell (RESET) button is pressed, the tune to be played is read from the switches. A pulse width modified square is output on an I/O pin, this drives a simple transistor to handle larger current to the speaker.

SCHEMATICS

to be added

PHOTOS

to be added

SOFTWARE

PIC binary code: doorbell.hex
Coming soon source code and ringtone download utility.

NOTES

Tweaking the output frequency was done using an oscilloscope to tune A to exactly 440Hz, from there all the maths is easy to generate a full range.