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.
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 for this project:
3. one buzzer
4.capacitors 100uf and .01uf
6. resistors 4.7k and 47k
|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
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.