on Friday, 4 October 2013
Lets start 'Circuit Project' series(posts) with a simple 'Light Sensor Circuit using LDR' project.
LDR Stands for 'Light Dependent Resistor' its a sensor. Resistance of  LDR varies depending upon the light fall on it.

Observe the circuit diagram below, whenever the light intensity is high which falls on LDR then LED 'D1' glow bright, when we place our hand on the LDR and restricts the light to fall on the LDR then depending upon the intensity of light, LED brightness varies. Note that transistor is acting like a switch between LED and Ground.

ldr circuit

Here we are using resistors, transistor, 5v voltage source and LDR .
We know how to find the value of the resistor which we have learn in our previous post, if you dont know click on link.
We have also seen how to find the Emitter , Base and Collector of the transistor, read it here
To know how to find the polarities of the LED then check this link
We will not find the battery of 5v in the market, we will get 9v battery which is very cheap too. So first we need to convert the 9v to the 5v and then fed it to our circuit.Look at the circuit diagram below

7805 is an IC which converts voltage(5v-18v )input to the stable 5v output. Connect this output to the first circuit(LDR circuit). Note this is the way we convert our 9v to the 5v and power to our microcontroller in our projects.
Look overall circuit below

ldr project

bc547 emitter base collector

First wire this circuit on the breadboard, if you dont know how to use breadboard then check this link

Output video is given below , watch it



Deyan Simeonov said...

The HUMANOID robotic ARM using pic microcontroller The purpose of the HUMANOID robotic ARM project is to implement the position control and vision control on the robotic arm. Which in my opinion is one of the best things happening and even KLDS and talked about this. said...

youstron thank you very much for this series of post i recently started my journey through micro-controllers.
i was able to carry out this project on Proteus and it worked fine how ever i like to get a full understanding of every operation, i came to the understanding that the varying led brightness was due to current division rule between the ldr and the resistor, however i was lost on the significance of the transistor in the circuit so i took it off (shorting d1 and r3), with this the led remained on irrespective of the change in ldr resistance.
i know i'm a bit late but you explanation will go a long way ...thank you

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