Musical Hold On For Telephone

by KNS Pvt Ltd
Save Rs. 50.00
Rs. 200.00
Rs. 150.00


The Musical Hold On for Telephone is an add-on external circuit that can be attached to the telephone to generate a melodious tune on the telephone line. The circuit allows the person on the other end to enjoy this melodious tune during the hold-on interval. To resume talking, just a simple switch needs to be flicked into the OFF position. A Red LED included in the circuit indicates that phone line is on-hold and it automatically turns OFF when the music stops. No. of ICs used: 1


Things which you can learn:
*Application of the melody generator IC UM66.
*Application of diodes for rectification and voltage regulation.
*Application of transistors for amplification and switching purposes.

Product Description

Build a cool Musical Hold on a device using simple components and fascinate your friends when you put them on hold.The heart of the Musical Hold-On for Telephone is the melody generator IC UM66. This IC generates a melodious musical tone when continuous power is supplied to it.


The circuit utilizes the voltage supply present on the telephone line, which is further applied to the bridge rectifier formed by four diodes (D1-D4). 

In a normal state with a switch (S1) kept in OFF position, no voltage is applied to the base of the PNP transistor MPSA92 (T1) and it remains reverse biased. Thus, the red indicator LED (D5) and the melody generator IC UM66 (IC1) are OFF and the phone line is free for normal usage. However, while talking if the switch (S1) is closed, then a positive DC voltage (available across the telephone line) gets connected to the base of transistor T1.

This forward biases T1 which acts as an amplifier and an electro-switch. A regulator circuit (comprising of resistors, a capacitor, and a zener diode) regulates the voltage available at the collector of transistor T1. The red indicator LED glows and IC1 also begins generating music as voltage gets applied to its Pin2. The low-value output from Pin1 is amplified by the NPN transistor BC547 (T2). This is coupled to the telephone line using a capacitor and thus the musical tune is heard on both phone.