Click here for Electronic Circuits main page
Click here for the circuit
Many a times one needs an ex- tra telephone ringer in
an ad- joining room to know if there is an incoming call. For
example, if the telephone is installed in the drawing room you may
need an extra ringer in the bedroom. All that needs to be done is to
connect the given circuit in parallel with the existing telephone
lines using twin flexible wires. This circuit does not require any
external power source for its operation. The section comprising
resistor R1 and diodes D5 and LED1 provides a visual indication of
the ring. Remaining part of the circuit is the audio ringer based on
IC1 (BA8204 or ML8204). This integrated circuit, specially designed
for telec- om application as bell sound generator, requires very few
external parts. It is readily available in 8-pin mini DIP
Resistor R3 is used for bell sensitivity adjustment. The
bell frequency is controlled by resistor R5 and capacitor C4, and
the repeat frequency is controlled by resistor R4 and capacitor C3.
A little experimentation with the various values of the resistors
and capacitors may be carried out to obtain desired pleasing tone.
Working of the circuit is quite simple. The bell signal,
approximately 75V AC, passes through capacitor C1 and resistor R2
and appears across the diode bridge comprising diodes D1 to D4. The
rectified DC output is smoothed by capacitor C2. The dual-tone ring
signal is output from pin 8 of IC1 and its volume is adjusted by
volume control VR1. Thereafter, it is impressed on the piezo-ceramic
Home | Tutorials | Books | Newsletters | Discussion Forum | Links | Downloads | Contact
Disclaimer: All the
information present on this site are for personal use only. No commercial use is
permitted without the prior permission from the authors of this website.
We cannot be held responsible for any
errors, omissions, or damages arising out of use of information available on
this web site. The content in this site may contain COPYRIGHTED information and should not be reproduced in any
way without the permission from us.