Want a doorbell with a twist?
This post shows you how to build a musical doorbell that plays a little tune instead of just a buzz!
It uses a special chip called a UM66T melody generator IC and only a few other parts.
This project is great for beginners because it is easy to build and fun to use.
You can even adjust how long the tune plays with a special time delay circuit.
What is a Musical Doorbell Circuit using IC UM66:
When the doorbell button is pressed, a simple electrical circuit called the Musical Doorbell Circuit employing UM66T generates a melodic melody.
A CMOS LSI Large Scale Integration melody generator integrated circuit IC for producing melodies is the UM66T.
The primary element in this circuit that creates the melodic sound is the UM66T IC.
Circuit Working:
Parts List:
| Category | Description | Quantity |
|---|---|---|
| Resistor | 100k | 1 |
| Capacitor | Electrolytic | |
| 100µF 25V | 1 | |
| Semiconductors | Transistors | |
| BC547 | 2 | |
| IC UM66 | 1 | |
| Speaker | 8Ω | 1 |
| Push Button | 1 | |
| Battery | 1.5V | 2 |
The UM66T series is a CMOS LSI designed melody generator IC intended for various applications such as doorbells, phones, toys, musical bells, home security alarm systems, and burglar alarms.
It incorporates an on chip ROM programmed for musical performances and operates within a supply voltage range of 1.5V to 4.5V.
Equipped with a built in RC oscillator this compact melody module can be utilized with minimal additional components.
Different UM66TXX series ICs can produce various tones based on their models.
The UM66T is a three pin IC resembling a transistor: the first pin is GND, the second is VCC and the third is OUT.
The doorbell circuit comprises a UM66T, two BC547 transistors an 8 ohm speaker and a set of resistors and capacitors.
On the input side, Transistor T1, Resistor R1 and Capacitor C1 form a time delay circuit, determining the duration of the bell sound.
The BC547 transistor acts as a switch toggling ON and OFF.
When a 3V supply is applied to the UM66T IC, it plays a pre programmed tune.
Pressing the push button charges capacitor C1 allowing transistor T1 to keep the IC playing the music until the capacitor discharges.
The discharging time, and thus the duration of the bell sound can be adjusted by replacing resistor R1 with a potentiometer.
A 100k resistor was used for full tone in this instance.
Transistor T2 drives the speaker, with pin 3 of the UM66 IC connected to its base.
Since the current output from pin 3 could be insufficient T2 amplifies the weak sound signals before playing the programmed sound loudly through the connected 8 ohm speaker.
Working of the Musical Doorbell:
Connect the components as per the circuit diagram and power the setup with a 3.7V Lipo battery.
When powered, capacitor C1 charges to full capacity.
Pressing the push button provides 3V to the UM66T across its supply terminals initiating the tune until the capacitor discharges.
The duration of the bell sound can be easily adjusted by substituting the R1 resistor with a potentiometer.
Formulas:
The UM66 IC, a melody generator IC, may be used to create a musical doorbell circuit using a simple setup in which the IC generates a melody sound when triggered.
The circuit above consists of below mentioned formulas to create:
Switching Transistors:
If you are utilizing the BC547 transistor as a switch, be sure it functions properly in saturation mode.
To make sure the transistor is completely on, use the following basic formula to find the value of the base resistor:
RB = Vin−VBE / IB
where,
- RB is value of the base resistor
- Vin is the input voltage (such as 3V from the battery) to the base resistor
- Base Emitter voltage, or BE, is equal to VBE (usually 0.7V for a slicon transistor).
- Base current desired IB
In order to guarantee saturation, IB should be around IC / β where, Vd is the transistors current gain (usually around 100 in the case of BC547).
Filtering of Capacitor:
The filtering capacitor aids in maintaining the stability of the UM66 ICs power supply.
An approximation of the formula for the capacitance needed to reduce ripples in a power supply is:
C = I * t / Vripple
where,
- C represents capacity in farads F
- I is amperes of current (A)
- t is the ripples duration in seconds (s)
- Vripple is the permissible voltage ripple expressed in volts V.
In the majority of audio applications, low current circuits such as the UM66 may be stabilized and noise is filtered by a 100µF capacitor.
Compute Resistor for Biasing:
Use the following when creating the base resistor for transistors, particularly when integrating with the UM66 or managing current:
IB = Vpushbutton−VBE / Rbase
where,
- Pressing the push button causes the voltage to increase Vpushbutton.
- Base Emitter voltage is equal to VBE (usually 0.7V for BC547).
- Rbase is value of the base resistor
If this is to be used as a switch, make sure IB is high enough to push the transistor into saturation state.
These equations aid in ensuring that all of the circuits parts operate as intended.
How to Build:
Building the musical doorbell using the UM66T melody generator IC involves following process to assemble the components and make the necessary connections.
Connect UM66T IC:
- Place the UM66T IC on the PCB.
- Connect pin 1 to the ground.
- Connect pin 2 to the positive supply.
- Connect pin 3 to the base of the BC547 transistor T1.
Time Delay Circuit T1, R1, C1:
- Connect the emitter of T1 to the ground.
- Connect the collector of T1 to one end of resistor R1.
- Connect the other end of R1 to one end of capacitor C1.
- Connect the other end of C1 to the positive supply.
- Connect the junction of R1 and C1 to the base of the BC547 transistor T2.
- Connect the collector of T2 to the positive supply.
- Connect the emitter of T2 to the ground.
Speaker Amplification T3, T4:
- Connect the collector of T3 to the positive supply.
- Connect the emitter of T3 to the ground.
- Connect the base of T3 to pin 3 of the UM66T IC.
- Connect the collector of T4 to the positive supply.
- Connect the emitter of T4 to the ground supply.
- Connect the base of T4 to the collector of T3.
- Connect the speaker across the collector of T4 and the ground.
Push Button and Power:
- Connect one terminal of the push button to the ground.
- Connect the other terminal of the push button to the junction of R1 and C1.
- Connect the positive terminal of the battery to the positive supply.
- Connect the negative terminal of the battery to the ground.
Test the Circuit:
- Power the circuit using the 3.7V Lipo battery.
- Press the push button to test the musical doorbell.
- Adjustments can be made to the potentiometer for desired sound duration.
Finalize the Circuit:
- Once satisfied with the performance, you can finalize the circuit on a PCB for a more permanent setup.
Conclusion:
Remember to exercise caution while handling electronic components, and ensure proper soldering and insulation to avoid short circuits.
If you are unfamiliar with electronics consider seeking assistance from someone experienced.
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