Here the circuit diagram of musical bell with touch switch and timer. This circuit is designed around CMOS IC CD4011 which work as the delay timer and IC UM66 which is well-known musical sound generator. When touch plates are bridged (touched) by hand for a moment, the circuit will start to produce music sound. Just after a short period (few seconds), the musical sound from this circuit will automatically stop.

The highest value of power source voltage for this particular circuit is +5 volts. The IC UM66 is unable to work over 3.3V voltage. IC 7805 regulator based power supply can certainly be applied to power this circuit.

Time delay can be adjusted by modifying the values of resistor R2 and capacitor C1. Three silicon diodes joined in series between pin 2 of UM66 IC and positive 5-volt rail maintain voltage carried out to pin 2 of UM66 less than 3.2 volts considering the decrease of about 1.8 volts across them.

Assemble the circuit and enclose into the plastic case. It suggested that the 5V regulated power supply also made and built in the case. Create some holes for switch, loudspeaker, mains power cable and port to the touch plate. Good luck…