What is a Breathing LED Circuit?
A Breathing LED circuit is a simple electronic circuit that fades in and fades out periodically. These fancy breathing LEDs are mostly used for decorative purposes in applications such as advertisement banners, Christmas lights, street signs, etc. Generally, almost all breathing LEDs follow the same configuration scheme, an astable multivibrator generates a free-running square, whose frequency is being regulated by a simple RC circuit connected in parallel to the multivibrator. The RC circuit allows the user to control the fade duration of the LEDs. So, in today’s tutorial, we are going to go over a step by step process on How To Make a Breathing LED Circuit Using LM358 Op-Amp IC.
The heart of this circuit is an LM358 IC. LM358 is a dual op-amp IC. . It can be considered as one half of the LM324 Quad op-amp which contains four op-amps with a common power supply. Here, we are using the LM358 in Astable multivibrator mode. An astable multivibrator is a free-running oscillator that switches continuously between its two unstable states. With no external signal applied, the transistors alternately switch from cutoff to saturation state at a frequency that RC time constants of the coupling circuit determine. If these time constants are equal (R and C are equal) then a square wave will generate with a frequency of 1/1.4 RxC. Hence, an astable multivibrator is also a pulse generator or a square wave generator.
Hardware Components
You will need the following parts to build this project:
| S.No | Component | Value | Qty |
|---|---|---|---|
| 1) | Op-Amp IC | LM358 | 1 |
| 2) | Transistor | S8050, NPN | 1 |
| 3) | Diode | 1N4007 | 1 |
| 4) | Potentiometer | 100K | 1 |
| 5) | LED | 5mm, 3.5V | 8 |
| 6) | Capacitor | 22uF | 1 |
| 7) | Resistor | 47K, 100K, 39K, 100 Ohm | 7 |
| 8) | Soldering Iron | 45W – 65W | 1 |
| 9) | Soldering Wire with Flux | – | 1 |
| 10) | DC Battery | 9V | 1 |
| 11) | Battery Clip | – | 1 |
| 12) | Veroboard | – | 1 |
| 13) | Jumper Wires | – | As per need |
LM358 Pinout
Useful Steps
1) Solder the LM358 IC on the veroboard.
2) After that, solder a 100K resistor between pin 7 & pin 5 of the IC.
3) After that, solder the three 4.7K resistors. the first resistor between pin 8, pin 6 & pin 3 of the IC. the second resistor between pin 4, pin 3 & pin 6 of the IC. lastly, solder the third resistor between pin 7 & pin 2 of the IC.
4) After that solder a 100K pot between pin 1 of the IC and the 39K resistor. Also, solder the 39K resistor with pin 5 of the IC.
5) After that, solder the +ve terminal of the 22uF/16V capacitor with pin 1 of the IC & the -ve pin with pin 2 of the IC.
6) Solder the base terminal of the S8050 transistor with pin 1 of the IC & the collector terminal with pin 8 of the IC.
7) Solder the cathode pin of the 1N4007 diode with pin 8 of the IC & the anode terminal with the +ve pin of the 9V battery.
8) After that, solder the four LED pair in series.
9) Now, solder the two 100 Ohm resistors between the emitter pin of the transistor and the +ve terminal of the LED.
10) After that, solder the +ve terminal of the battery clip with pin 8 of the IC and the -ve terminal with pin 4 of the IC.
11) Power up and test the circuit.
Working Explanation
The working of this circuit is based on the principle of using an astable multivibrator to generate a free running square wave and then to regulate the frequency period of the square wave signal by controlling the RC values at the input of the Op-Amp IC. On powering up the circuit, the LM358 IC, connected in astable multivibrator mode, generates a free running square.
The output frequency of the square wave is regulated by connecting an RC circuit in parallel to the inverting input of the LM358 IC. The value of the R (47K) and C (22uFF) are adjusted with respect to the delay time period desired. The amplifier output then serves as a control signal on the base of the S8050 transistor. The output of which triggers the LED to slowly fade in and out with respect to the time constant of the amplifier output. You can tune the sensitivity of this circuit by using the 100K preset pot.
Applications
- It is mostly used in places such as road signs, billboards, advertisement banners, etc.
- Also used as an introductory tool to help beginners familiarize with the concept of multivibrators,
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