HOW TO MAKE A DARK SENSOR USING LDR and 555 TIMER

This LDR and 555 timer  based DARK SENSOR indicates the absence of light or presence of dark in a certain region. 

Whenever the intensity of light falling on this circuit(sensor) is below a certain value, a buzzer connected to the output of IC 555 timer will produce sound and thereby act as a DARK SENSOR.

To make this Dark Sensor, we need two most important components:

A) 555 IC:

IC 555 timer is one of the most common and popular IC  among electronic hobbyist and engineers, even after more than 46 years of its invention.

Due to its wide range application in electronics, many projects can be easily made using this IC. 555 timer is used for many purposes in electronic industry as a monostable and astable multivibrator. 555 timer can also be used as a DARK SENSOR in its monostable mode or single shot mode.

Now, apart from 555 timer we also need one ldr(light dependent resistor) to build this 555 TIMER project. Work of LDR is to sense the light in surrounding and then send the details to 555 timer.

 

B) LDR:

 

LDR or Light Dependent Resistor is a special kind of variable resistor, which changes its resistance according to the intensity of light falling on it. As the intensity of light increases its resistance decreases. We need this property of LDR for our DARK SENSOR.

 

 

COMPONENTS REQUIRED:

 

Components required for this project:
1.555 timer
2.one ldr
3. one buzzer
4.capacitors 100uf and .01uf
5.9volt battery
6. resistors 4.7k and 47k

 

CIRCUIT DIAGRAM:

 

 

CIRCUIT DIAGRAM

 

 

 

PIN NO. CONNECTION
1  GND  To -ve terminal of battery
2  TRIGGER  Between LDR and 4.7k resistor
3  OUTPUT  To Buzzer
4  RESET  To +ve terminal of battery
5  CONTROL  To .1uf capacitor
6  THRESHOLD  Between 47 k resistor & 100 uf capacitor
7  DISCHARGE  Between 47 k resistor & 100 uf capacitor
8  VCC  To +ve terminal of battery

 

 

 

COMPONENT  CONNECTION
LDR  Between 8 pin and 2 pin
4.7K  Between 2 pin and 1 pin
.1UF cap.  Between 5 pin and 1 pin
100 uf cap.  Between 6 pin and 1 pin
47k res.  Between 7 pin and 8 pin
Buzzer  Between 3 pin and 1 pin

 

Want to know how 555 timer works?

Check out this awesome blog post at electronicsforu.com

 

WORKING:

Watch this video to see ‘DARK SENSOR’ in action!

 

Two important points to consider in a 555 timer:

 

A. Output or Pin 3  of 555 timer will be 1(HIGH) only when voltage at pin 2  or trigger pin is less than 1/3v of the applied voltage at Vcc pin of 555. 

Since battery is of 9 volt, hence : 

1/3 of 9 = 3 volts

 

B. Capacitor (100 uf) discharges through discharge pin (7th) to ground as soon as voltage at 6 pin or threshold pin of 555 timer is greater than 2/3v of the applied voltage at 8 pin or Vcc pin.

2/3 of 9 = 6 volts

 

 

CASE1- when light falls on LDR

In this case resistance of LDR is minimum so all voltage drop is across 4.7k resistor, due to which voltage at pin 2 or trigger pin is greater than 1/3 of 9v causing reset of flip-flop inside the 555 timer and thus zero voltage at output(pin 3) . Now since output pin is directly connected to buzzer, it produce no sound.

 

 

CASE2- when no light falls on LDR

In this case resistance of LDR is maximum so all voltage drop is across LDR, due to which voltage at pin 2 or trigger pin is less than 1/3 of 9v causing set of flip-flop inside the 555 timer and thus one as output(pin 3). Now since output pin is directly connected to buzzer, it produce beep sound.

 

 

1 Comment

One Reply to “HOW TO MAKE A DARK SENSOR USING LDR and 555 TIMER”

  1. I simply had to thank you very much yet again. I am not sure what I could possibly have taken care of without the type of tips and hints shown by you relating to my theme. It previously was an absolute frustrating matter in my position, nevertheless coming across the expert technique you solved it made me to jump over fulfillment. I am just happy for your information as well as wish you comprehend what a great job your are carrying out educating others all through your blog post. Most likely you haven’t met any of us.

Leave a Reply

Your email address will not be published. Required fields are marked *

%d bloggers like this: