Tuesday, February 14, 2017

Musical Doorbell

This post is about making a simple musical doorbell circuit that can be used in your house and might take only couple minutes to build it.

Goal here is pretty simple, it will be a musical doorbell that has a very small power consumption and can play the music for couple moments even after releasing the momentary doorbell switch. For the music we will be using a melody generator integrated circuit to make our work easy and to turn on and keep it on we will be relying on Capacitor and transistors, so let's take a look at the component list.


Component List.

1. Integrated Circuit UM66.
2. Transistor 2N3904, 2N3906, SS9013, one piece each.
3. Capacitor 100uF.
4. Resistor two 1Kohm, and one 10kohm and one 100kohm.
5. Battery holder, two AA type.
6. Speaker 4/8ohm.
7. Momentary press button.


Let's talk about music!

Part number of the UM66 will give us an idea of what music it is going to generate. To find the right music for doorbell buy the one with the right part number.



The diagram!

Now that we know which Integrated circuit to order let's build the circuit.



How does it work? 

Power source for this circuit is two AA size cell, preferably Alkaline. They will provide roughly 3V.

When SW1 or the momentary press button is pressed the 100uF capacitor will be charged and at the same time the 2N3904 transistor will start conducting as it is getting current to it's Base.

As the 2N3904 can now be treated as a close switch we can assume the Base of 2N3906 to be at the ground which will cause the 2N3906 to start conducting.

Now we can see the current can enter into the integrated circuit causing it to turn on. This circuit will output a melody signal which will be amplified using SS9013 transistor which is feeding a loud speaker.

If the momentary switch is released, the 100uF capacitor will discharge through the 10kohm resistor and the 2N3904 transistor. So it will keep the circuit alive for couple moments after releasing the switch. Once it is fully discharged both the transistors will be open again and the integrated circuit will not get any power to stay On.


Note:

1. You can use ZL66 instead of UM66 too.
2. Two AA Alkaline cells will be fine for this doorbell.
3. A normal 1-3W speaker will be fine.
4. Increasing the value of the capacitor will cause the circuit to stay alive longer after the press button is released.
5. Both the 2N3904 and 2N3906 can be replaced by similar NPN and PNP transistor respectively.


Resources:

1. UM66 Datasheet.
2. SS9013 Datasheet.
3. Read my other posts.