Your First Ever Sensor Circuit

The simplest sensor for detecting a light is a photo resistor which is otherwise known as Light Dependent Resistor. This component works by changing its resistance by the amount of light incident on to it.
To work out with a Light Dependent Resistor or a photo resistor, just go through the project described below.  

For this you'll be needing the following components
  1. Photo resistor
  2. An LED
  3. 470-ohm resistor
  4. Bread board
  5. 9v battery clip
  6. 9v battery

How to build it:

  • The very first step  would be orientation of your bread board.
  • Now identify the terminals of your LED. Generally, the bigger one is positive and the smaller one is negative. 
  • Insert the LED into bread board. 
  • Insert the photo resistor so that the negative lead of the LED and one of the photo resistor leads occupy the same column. The second LED should occupy its own column.
  • Now take a 470-ohm resistor and add it to the column where the positive of the LED is.
  • Attach the negative terminal i.e. black wire from the battery clip to the column that contains only a photo resistor lead.
  • Insert the positive terminal i.e. red wire from the battery clip to the column that contains only a resistor lead.
  • Now connect the 9v battery to the battery clip.

In the above circuit value of R2 is 470-ohm and R3 is nothing but an LDR/Photo Resistor

You're done with your circuit. Now it's time to check the functioning of the thing you've made.

Working:

Light Dependent Resistor or a photo resistor works on the very basic principle of resistance. when more light hits the photo resistor, the resistance of it gets reduced. And if the light falling on the photo resistor is quite dim or whenever it is in dark such that the resistance increases. So, in above project whenever the light falls on the photo resistor, you observe that the intensity of the LED is changing. When it is exposed to light of higher intensity, the LED glows with a greater brightness this is since the resistance is reduced which in turn allows the LED to glow with maximum brightness.

Now observe the same LED by placing your finger on LDR. The opposite happened right? This is because whenever the photo resistor is getting dim light or no light at all, the resistance of the photo resistor gets increased. Due to this the LED is getting dimmer.

The current flow through the sensor controls how bright the LED will shine. This circuit is designed in such a way that all the current to the LED must pass through the photo resistor first.

Hope you've enjoyed your first ever sensor circuit.

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