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# Build LED blinking circuit with 555 oscillator

This project is to build an LED flashing circuit on a breadboard.

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This project is to build an LED flashing circuit on a breadboard, but the main control used is not a single chip microcomputer, but a classic 555 oscillator.

Why use a 555 oscillator?

Because the principle of the 555 oscillator is simple but powerful, there are only 26 transistors inside. Even if the internal schematic diagram of the 555 oscillator is given to us, we can analyze its working principle through analysis. Not only that, but also Learn the knowledge of analog electricity and digital electricity.

For example, the trigger inside 555 is a category of digital circuits, and to understand this trigger, we must learn the knowledge in "Digital Electronic Technology". If we understand the trigger, we can basically get started with digital electronics.

Not only that, the 555 oscillator is more about the knowledge of modulo electricity, so in the 555 oscillator, we can also learn a lot of basics about it.

Due to the advancement of science and technology, people nowadays tend to be overly ambitious to start learning from STM32 and RTOS. Even if they can use library functions to operate the single-chip microcomputer, they don’t know anything about the bottom layer of it, or even do not know what triggers are.Such learning is not rigorous.

To sum up, we believe that the 555 oscillator should not be abandoned because of the current technological progress. Quietly on the contrary, if we really want to have a deeper development in a certain industry, we should study the most basic knowledge and be down-to-earth.

Now I will build an LED flash circuit with a 555 oscillator, hoping to inspire you guys' interest in learning the underlying electronic circuit. Check this part in the instruction.

• 1
What is 555 oscillator

Simply put, the 555 oscillator is an integrated circuit that can output a pulse signal of a specific frequency.

The little guy below is a 555 oscillator, does it look like a little crab? Crabs are definitely delicious in everyone's minds, but when asked to study an integrated circuit with the same number of claws as crabs, you may not have the patience.

Don’t worry, I will try to help you eat this small black box with only 8 pins like a crab.

You can check the specification here.

• 2
Internal structure

To know how an integrated circuit works, we first need to know its internal schematic diagram. The internal schematic diagram of the 555 oscillator is shown in the figure below.

Fortunately, there are not many internal integrated transistors, only 26. You have to  know that the A12 X chip used in the iPad Pro integrates more than 10 billion transistors, and even the A12 of the iPhone XS integrates several billion of them. Although they are all chips, they are similar in size. It can only be said that the advancement of science and technology is so surprisingly fast.

For the above schematic diagram, it should be difficult to understand if you have not studied digital or analog electricity. Even if you have learned it, you may not be able to understand it. Although there are only 26 transistors, the knowledge involved is extremely wide, almost all of the university’s digital, electrical and analog electronics.

It doesn’t matter if you don’t understand it. The following is the simplified schematic of the 555 oscillator. The colored parts are modular, corresponding to the comparator and the trigger. Their names sound similar, but one belongs to the analog circuit, and another belongs to the number of electricity.

We only analyze the schematic diagrams now, not involving their construction principles, because if we talk about them, it is tantamount to relearning the analog electronics, and we may not be able to finish it with 10 articles.

• 3
Principle block diagram

The simplified block diagram is very easy to understand. Each block diagram corresponds to the colored circuit in the figure above.

The yellow triangle and the pink triangle below are two comparators, and the purple one on the right is an R-S flip-flop.

The green ones on the left are three resistors with a resistance value of 5K. This is also the origin of the name of the 555 oscillator. There is also an oscillator with 556. Can you guess the difference with 555? At this time, you might say that in addition to the two 5K resistors, the other one is a 6K resistor.

Is it really like this? This is not the case. The 556 oscillator has an additional 1 than the 555, but this 1 does not represent the resistance of 1K, but two 555 oscillator modules contained in the 556. Such naming is truly surprising. If I were to name it, I might name 556 as 555D, and D represents double.

The picture below is a simplified diagram of the various functional modules inside the 555. It doesn't matter if you still can’t understand it, because we can use this 555 oscillator directly, even if you don’t know how it works.

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