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…

Here the touch switch schematic diagram:

Components list:

Part      Total Qty.    Description

C1         1          10uF 16V     Electrolytic Capacitor
R1, R2     2          100K 1/4 Watt Resistor
R3         1          10 Meg 1/4 Watt Resistor
U1         1          4011 CMOS NAND Gate IC
MISC       1          Board, Wire, Socket For U1

Touch Switch Circuit Notes:

1. The contacts an be made with just two loops of wire close together, or two squares etched close together on a PC board.
2. When activated, the output of the circuit goes high for about one second. This pulse can be used to drive a relay, transistor, other logic, etc.
3. You can vary the length of the output pulse by using a smaller or larger capacitor for C1.

Just try touch switch circuit…