555 Timer Based Simple Projects Ideas

555 Timer Based Simple Projects:

Electronic Detector Projects based on 555 Timer:

To start to play with electronics the 555 timer IC is an ideal choice. We can built an interesting circuits with the help of this 555 timer IC. In practical if the expected result is not achieved, we can troubleshoot the circuit very easily.

In this post we are going to understand about the 555 timer based detector circuit. This is designed so that it will raise the alarm whenever fault happens. Using this concept we can generate many ideas and build numerous projects.


Components required to build this circuit:

  1. Timer IC 555 - 1No
  2. LDR - 1No
  3. Resistance  - 1K, 100K, 47K, 5 Ohm
  4. Capacitor - 33uF, 0.01uF, 0.05uF
  5. Diode
  6. Speaker - 16 Ohm

Circuit Operation:

  • As shown in the circuit, it has the 555 timer IC. This timer IC will be triggered by the LDR (Light Dependent Resistor).
  • In a dark situation, the resistance of the LDR is very high and in the illuminated situation, the resistance becomes low.
  • The LDR is made up of a light-sensitive material, like cadmium sulphide (CdS).
  • During the normal conditions the LDR is kept illuminated so no sound will be produced from the speaker.
  • But whenever the beam of light falling on the LDR is disturbed, then the resistance of LDR will become high.
  • So the 555 timer gets triggered. It leads to audible noise from the speaker which is connected to the 555 timer IC.

Circuit Application:

We had understand the fundamental working principle of the circuit. Now think yourself how can we use this concept in real life situations?
You might have 'n' number of ideas. One of the sample idea is discussed below.
The Light Dependent Resistor (LDR) along with the light beam source is to kept on the main door of the house. The light beam source is placed such that the beam falls directly on the LDR. The LDR should be mounted in a small box which is painted in a black color. The LDR should face the light beam source. It is mandatory to keep the LDR in the black color box, so that false triggering will be avoided in the normal room temperature.

LDR - Light Dependent Resistor:

  • To understand the circuit operation completely, it is good to refresh about Light Dependent Resistors (LDR).
  • The Light Dependent Resistor is made up of semiconductor material.
  • The cadmium sulphide (CdS) and cadmium selenide (CdSe) are the most frequently used semiconductor materials to build the LDRs.
  • These materials are most sensitive to the visible spectrum of the light.
  • The Cadmium Sulphide (CdS) is peaking at about 0.6μm.
  • The Cadmium Selenide (CdSe) is peaking 0.75μm. 
  • Their electrical characteristics will vary according to the amount of light fall on the device. As shown in the below characteristics, when the light intensity increases, the resistance of the LDR will decrease drastically.
  • For example, a standard Cadmium Sulphide (CdS) made LDR shows 1MΩ resistance at complete darkness. But under a bright light source, the resistance will become less than 1kΩ.  

Read More Electronics Projects for Beginners:

Simple 555 timer based LED Project
555 timer based Single Pulse generator
Multi Pulse Generator circuit Design using 555 IC
How the 555 Timer IC Operates Internally?
Fixed & Variable Pulse Generator Circuit Design Project

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1 Response

  1. sneha chaware says:

    keep posting

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