#### What Will I Learn?
At the end of this tutorial:
The readers will be able to know how to create an automatic sound signal using the principle of light dependent resistor. 
And also the reader will be able to apply this tutorial in creating electronic project that needs to be operated automatically, like household outside lights.
#### Requirements
Electronic Components 
♦ 9013 BJT
♦ LDR
♦ 1N4007 Diode
♦ 200 ohms Resistor
♦ 5k Potentiometer
♦ 5V Relay
♦ Breadboard
♦ 9V Battery
♦ Fuse
♦ Speaker
♦ PCB
♦ Connecting wires
♦ Switch
Software
♦ Fritzing application

#### Difficulty
♦ Intermediate

#### Tutorial Contents
Using the fritzing software, we will create our circuit diagram, PCB layout & prototype using the breadboard.

Part I. Schematic Diagram
So first let us construct our circuit diagram
1.	Open the fritzing software.
![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516075681/hhjbolfugsi40nzahfyy.png)
2. Select the electronic components needed for the circuit in the fritzing library.
![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516075702/w8tczmjwbfgobzvqyupg.png)
3.	Connect the circuit diagram.

![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516075721/l4imgblqcok1wnzvtepx.png)
Connect the positive terminal of the 9V battery to the LDR terminal.
![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516075737/nsapycfesm2t605ga5l8.png)
Then the other LDR terminal must be connected to the potentiometer. Just follow the connection below until it will look like the figure below.

This is the final circuit diagram.
![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516075768/dgysv4mzdm6cqsiaomop.png)
![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516075777/kcuvk3mxf3dmjzqhyamo.png)

The transistor acts as a switch in order to control the operation of the speaker automatically when the light dependent resistor detects lights. When there is light, the resistance of LDR will be low causing the voltage drop across the potentiometer to be high. Making the transistor operates.

![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516075797/ohq1lyhdqsbfubyltzyb.png)

When there is no light, the LDR resistance will decrease and causing the voltage drop across the base resistor of the transistor to decrease below threshold voltage. This will make the transistor off. Then the diode conducts, allowing the current to flow through.
![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516075814/ukjnkr9khq7xgqbgymih.png)
Then the current will trigger the relay to switch on, allowing the ac supply to trigger the speaker when the switch is on. That’s the time the speaker gives sound automatically.
![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516075831/gzvsltk1epexfymvenes.png)
The fuse is connected in series to the ac supply to protect the circuit from overcurrent. 

Part II. Breadboard

Now let us do the prototyping of our circuit using the breadboard.
Click on breadboard on the fritzing.
![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516075856/sxba9lxia6d9wywpqxt9.png)
Arrange each component in the breadboard. If you don’t know the basic information of a breadboard or you do not know how to construct circuit on breadboard just click this [link]( https://utopian.io/utopian-io/@rfece143/electronic-circuit-construction-a-step-by-step-guide-in-placing-and-constructing-a-basic-circuit-in-the-breadboard-using).

![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516075874/rkn021l65zvurkkzoftd.png)
After connecting each component, it will look like this.
![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516075894/xyibbk5tfznf4ey6fugy.png)

Part III. PCB layout
Click on PCB.
![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516075913/qgg6pxs79k4qnk7lejxz.png)
Arrange or design your circuit on the PCB
![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516075936/d7uasvmuvhmcuzctvgfe.png)

Click on the autoroute to enable the autoconnect for the circuit layout.
![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516075960/bd5h7f3zsur148tqzg1e.png)
Drag the connection according to your layout.
![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516075975/ykrow7hv6ecv5w9y3dif.png)
You can design your own PCB circuit layout.
![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516075994/rsarzjtblwqirgzfupwv.png)

Application 

You can change the output load to a light bulb. In this way, the bulb will light up when there is no light. But when the LDR detects light, the bulb will automatically turn off.

Sample actual picture* (All pictures are mine)*

![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516076024/z2bmgxhnabvehqfvfx46.png)

![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516076066/upc8ninltybddvodl5tz.png)
![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516076087/c80qyqq3o0p1keqoqyte.png)
![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1516076111/nbt1wdpu2wv3amhljzs9.png)

Actual Demonstration (This video is mine)

[link]( https://www.youtube.com/watch?v=TyE8f-JAKUM&feature=youtu.be)

#### Curriculum
Here are my other tutorials for electronic projects.

## ELECTRONIC PROJECTS 

[Tutorial 1]( https://utopian.io/utopian-io/@rfece143/electronic-circuit-construction-a-step-by-step-guide-in-placing-and-constructing-a-basic-circuit-in-the-breadboard-using)

[Tutorial 2]( https://utopian.io/utopian-io/@rfece143/electronic-project-how-to-create-a-simple-mechanism-in-dispensing-an-object-automatically-using-a-magnetic-solenoid)

[Tutorial 3]( https://utopian.io/utopian-io/@rfece143/electronic-project-2-how-to-create-a-6-led-light-sound-follower-circuit-using-fritzing-software-for-circuit-layout)

[Tutorial 4]( https://utopian.io/utopian-io/@rfece143/electronic-project-4-light-sensing-device-or-a-step-by-step-guide-in-constructing-a-basic-circuit-in-showing-the-function-of-an)

[Tutorial 5]( https://utopian.io/utopian-io/@rfece143/electronic-project-5-control-the-dc-motor-using-a-pushbutton-or-how-to-create-a-mechanism-to-control-the-movement-of-a-dc-motor)





<br /><hr/><em>Posted on <a href="https://utopian.io/utopian-io/@rfece143/electronic-project-6-automatic-switch-for-sound-signal-using-light-dependent-resistor">Utopian.io -  Rewarding Open Source Contributors</a></em><hr/>