This article will introduce several circuits for breathing lights.
1. Understand breathing characteristics and time parameters
Breathing is divided into two processes:
Inhalation: The exponential curve rises and the process requires 1.5S
Exhale: The exponential curve drops, the process requires 1.5S.
For adults, the average breath is 16 to 18 times per minute;
For children, the average breath is 20 times per minute;

The above parameters are the number of times in a uniform breathing situation. Can be used to make an indication of sleep.
3, breathing light circuit

Component name
5mm LED highlight blue light 1
LM1458N (or HA17458) dual op amp 1
2N3904 (8050, 8550) NPN Transistor (TO92 package) 1
22uF 100V /47uF 35v / 47uF 50V capacitor 1
47K [1/4w] 4
100K [1/4w] 2
100 ohm 1
Description:
Changing the capacitance or the size of R3 can change the breathing rate.
After the experiment, R3 changed to two 47K resistors in series, the effect is better, the frequency of breathing is more appropriate.
In addition, three 1N4007 on the input voltage string are lowered, so the effect will be better, and the breathing lamp will have a short extinguishing time. (Only suitable for green and blue LED lights, red LEDs will not have extinguishing time because the luminous voltage is relatively low, you can string some 1N4007 to achieve the effect)
In addition, LM1458 is a dual op amp, almost all with NE5532, CA1558, etc. As for the working voltage, remove the input 100 ohms, directly on 7.2 is no problem~
A Taiwanese netizen's breathing light circuit

Another breathing light circuit

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