In this tutorial, we are going to make a Touch Door Bell Alarm Circuit which will sound a melody with just a touch of a finger. This project uses a TTP223 capacitive touch sensor module which gives input to the musical IC that is amplified by  NPN transistor and hence melody is played on the speaker. Let’s make this Project.


BC547 Pinout

BC547 Pinout


BC547 Datasheet

Model No.

BC 547

DC Current Gain (hFE)

Min: 110     Max:800

Collector Current (IC)

100 mA

Collector Power Dissipation

500 mW

Collector-Base Voltage (VCBO)

Max:  50V

Collector-Emitter Voltage (VCEO)

Max:  45V

Emitter-Base Voltage (VEBO)

Max:  6V

Junction Temperature

150 °C

Storage Temperature

-65 ~ 150 °C


BT66 Pinout

BT66 Pinout


BT66 Datasheet

Operating Voltage

Min: 1.3V    Max: 3.3V

Supply current


Frequency Operating

Min: 57Hz    Max: 82Hz

Operating Temperature

-20 to 65 oC


TTP223 Pinout

TTP223 Module Pinout


Touch Door Bell Alarm Working

When the touch sensor is touched a 3.7V signal is generated at the IO pin of the sensor. This pin is connected to the Vdd of Musical IC. Its output pin is connected to the Base of a transistor that acts as an amplifier and hence a melody is created and can be heard by the speaker. 


Musical IC - BT66

BT66 is easy to use three-terminal Melody generator IC. It can be used where the tone has to be played as a notifier. It consumes very little current (1uA) hence increasing battery life. There are many applications of this melody IC. In case you want a different tone you have to use a different IC with a different Model number. In our case, we are using BT66T-68L.


IC  Model Number

Tone name



Jingle Bell



For Elise



Happy Birthday



Love Story



It’s a Small World


Features of Musical IC:

  • Plays a melody consisting of 64 Notes
  • Lower range of operating voltage form 0.3V to 3.7V
  • Typical Operating Voltage: 3.3V to 3.7V
  • Can easily drive a speaker through NPN Transistor as we did here.


Components Required for Door Bell Alarm


Touch Door Bell Alarm Circuit Diagram

Touch Door Bell Alarm Circuit Diagram

In the above circuit diagram, the touch sensor module has three pins. Vcc is supplied with a positive of 3.7v battery. GND is connected to the negative terminal of the battery. Its signal pin is connected to the Vdd terminal (or Vcc terminal) of Musical IC.

UM66 has 3 pins too whose GND is connected to GND its output is fed into the base of the transistor. This transistor is acting as an amplifier. The transistor emitter terminal is connected to the GND and its collector terminal is connected to the negative of the speaker. The positive of the speaker is connected to the Battery’s positive terminal. In this way, our circuit connection is done.



Circuit not working?

Ensure that your circuit is according to the circuit diagram and you must check BJT, touch sensor and Melody IC that they must be in good working condition.

No power supply?

The Battery used here is 3.7 volts. Less than this voltage rating,  the circuit may malfunction.

Can we use higher rating of speaker?

Yes, we can use a higher rating of the speaker like 0.5 watts. You will get a louder sound but it will consume more power.

Touch sensor is not responding?

In this condition check your touch sensor with a multimeter. Apply 3.7 volts to the Vcc pin and connect ground to ground. Now take a multimeter and connect the positive probe to the OUT pin and the Negative probe to GND. Now touch a sensor, if the Multimeter shows output on touching that means it is in good working condition.


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