Are you looking for a special doorbell?
Instead of just buzzing this tutorial shows how to create a musical doorbell that plays a small melody!
It just uses a few extra parts including a unique chip known as a UM66T melody generating IC.
Because it is simple to construct and enjoyable to use this project is excellent for beginners.
Even the duration of the song can be changed using a specially designed delay circuit.
What is a Musical Doorbell Circuit using IC UM66:
A simple electrical circuit known as the Musical Doorbell Circuit using UM66T generates a melodious tune when the doorbell button is pressed.
The UM66T is a CMOS LSI Large Scale Integration melody generator integrated circuit used to create melodies.
The UM66T IC is the main component in this circuit that produces the melodic sound.
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 |
Doorbells, phones, toys, musical bells, home security alarm systems and burglar alarms are just a few of the devices that are designed to use the UM66T series a CMOS LSI melody generator integrated circuit.
It functions within the 1.5V to 4.5V supply voltage range and has an on chip ROM that is set up for musical performances.
With its integrated RC oscillator this little melody module requires few other parts to operate.
Various ICs in the UM66TXX family may generate different tones according to their models.
GND, VCC and OUT are the first, second and third pins of the UM66T a three pin integrated circuit that resembles a transistor.
A UM66T, two BC547 transistors, an 8 ohm speaker and a number of resistors and capacitors make up the doorbell circuit.
The time delay circuit formed by Transistor T1, Resistor R1 and Capacitor C1 on the input side controls how long the bell sound continues.
Toggling ON and OFF is done using the BC547 transistor acting as a switch.
The UM66T IC plays a already programmed song when a 3V supply is supplied.
Transistor T1 will continue to play music until capacitor C1 discharges because pressing the push button charges it.
You may change the discharge time and thus the bell sounds duration by replacing a potentiometer for resistor R1.
In this case full tone is possible with a 100k resistor.
Pin 3 of the UM66 IC is connected to the base of the transistor T2 which powers the speaker.
The weak sound signals are enhanced by T2 before the programmed sound is played firmly through the connected 8 ohm speaker since pin 3s current output might not be enough.
How the Musical Doorbell Operates:
As shown in the circuit diagram connect the parts, then use a 3.7V Lipo battery to power the circuit.
Capacitor C1 fully charges when switched on.
When the push button is pressed 3V is sent to the UM66T across its supply terminals starting the tune until the capacitor drains.
It is simple to change the bell sounds duration by using a potentiometer in place of the R1 resistor.
Formulas:
Using a simple configuration the UM66 IC is a melody generator IC which is used to build a musical doorbell circuit that when activated produces a melodic sound.
The circuit above uses the formulas that are provided below to generate the following:
Transistors that switch:
Make sure the BC547 transistor operates correctly in saturation mode if you plan to use it as a switch.
Use the following simple calculation to get the value of the base resistor in order to confirm that the transistor is fully on:
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 which is 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 which is usually around 100 in this circuit for BC547.
Capacitor Filtration:
The filtering capacitor helps to keep the power supply for the UM66 IC stable.
An estimate of the capacitance required to reduce power supply ripples is as follows:
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 most audio applications a 100µF capacitor can filter noise and maintain low current circuits like the IC UM66.
Calculate the Biasing Resistor:
When building the base resistor for transistors particularly when controlling current or integrating with the UM66 use the following:
IB = Vpushbutton−VBE / Rbase
where,
- Pressing the push button causes the voltage to increase Vpushbutton.
- Base Emitter voltage is equal to which is usually 0.7V for BC547.
- Rbase is value of the base resistor
Make sure the IB is high enough to force the transistor into saturation if this is going to be used as a switch.
Making sure that every component of the circuit functions as planned is made easier by the above formulas.
How to Build:
To build a Simple Musical Doorbell Circuit using IC UM66 following the below mentioned steps for 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.
Power and Push Button:
- Connect a push button one terminal to the ground.
- Wire the other end of push button terminal to the intersection of R1 and C1.
- The batteries positive terminal should be connected to the positive supply.
- Connect the batteries negative terminal into the ground.
Test the Circuit:
- Power the circuit using the 3.7V Lipo battery.
- Press the push button to test the musical doorbell.
- To get the required sound duration the potentiometer should be adjusted
Complete the Circuit:
- After being happy with the performance one may complete the circuit on a PCB for a more long lasting design.
Conclusion:
To prevent short circuits be careful while working with electronic components and make sure that the soldering and insulation are done correctly.
Consider getting help from an expert if you are not comfortable with electronics.
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