super simple bell extension

hear the telephone ringing where you are, not where it is This has got to be one of the simplest electronic bell extension cir- cuits ever designed. In all it contains just seven components and none of them are even slightly unusual. They are the kind of parts that most elec- tronic hobbyists will probably have lying around somewhere, and these seven components are all that are needed to make a universal telephone bell extension circuit. The telephone bell operates on an a.c. voltage so this must be rectified by the four 1N4148 diodes in order to make it suitable for the d.c. buzzer. Obviously, the voltage across the buzzer cannot be allowed to rise too 84411 8-02 high so a resistor is connected in series with the rectifier and a zener diode across the buzzer. The values used give a voltage of about 5 V across the buzzer, but, depending on the type selected, this can quite eas- ily be changed. Furthermore, if the input voltage is more than about 10 V a.c. the value of the series r...