[Basic] How to read circuit diagram for beginners 

In this video I'll show you how to read circuit diagram briefly.
Even though you are not an electric engineer, I'm sure you can understand it.
-Table of Contents
0:00 Opening
0:19 Basic rule of circuit diagram
2:23 Circuit symbols that are necessary to remember
4:10 Points when reading circuit diagram
5:16 Conclusion
-Introduction
Hardware engineer
9 years experience as a Maker
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-Content
First, we will discuss the basic rules of schematics that you should at least know.
There are no absolute rules for schematics, but there are some conventions that should be easy to read for everyone. There are four such conventions, roughly speaking, as follows. I will introduce them one by one using the published Arduino schematics as examples.
The first one is that electricity flows roughly from left to right. For example, in this part of the circuit, the power supply voltage VIN is input on the left side, and the voltage divided by the resistor enters the comparator and is output on the right side. The signal is input to the FET, which also receives a signal from the left side, and when the FET turns on, the signal is transmitted to the right side, where a 3.3 V voltage is output from the right side through the three-terminal regulator. Although a quick glance at the schematic does not show the direction of the current, it will be easier to read and understand if you keep this basic gesture in mind.
The next step is to write the higher voltage at the top and the lower voltage at the bottom. Voltage is often compared to a dam, so this image should be easy to understand. As you can see from the schematic, in many places the voltage was written on top.
The next thing is that the parts connected by the same wire are at the same voltage level. For example, in this section, they are connected to each other, which means they all have the same voltage applied to them. This rule remains the same no matter how far apart the lines are.
The last thing is that if the power supply, GND, and label have the same name, they are connected to each other. For example, in this schematic, there are many power supplies named +5V, but they are all connected in the circuit. There are also signals with the same name, USBVCC, here and here, which are separated on the schematic but are actually connected to each other. This is done to reduce the number of lines as much as possible to avoid messing up the schematic. Where to cut is completely up to the schematic designer's taste, so it is up to the individual.
Next, here are some circuit symbols that you should at least memorize.
If you memorize the circuit symbols in advance, it will be much easier to read the schematic, so let's keep them in mind here. So, I have compiled a list of them.
First, here are the circuit symbols for the very basic electronic components. Resistors are used equally in this jagged or square one. Capacitors are marked with a plus sign on one side if they are of the oriented type like electrolytic capacitors. Diodes and LEDs have the same element structure, so the same symbol is used only with or without an arrow to indicate light. Transistors and FETs are each of two types, differing only in the direction of the arrow. Transistors are easy to remember because the direction of current flow matches the direction of the arrow, but FETs may be a little harder to understand sensibly because they represent the direction of parasitic diodes that are created in the device due to its structure.
This is a power supply, and the symbol used differs depending on whether it is DC or AC.
GND and ground are sometimes used interchangeably, but they have strictly different meanings, as GND is the voltage reference point in a circuit and ground is the connection point to the earth. Signal lines are used to connect distant locations on a circuit diagram. The direction of the arrows matches the direction of the input and output, making them easy to read and understand. For wiring, black circles are placed where wires are connected to each other. It is said that it is better to avoid making crosses on a schematic because it is sometimes difficult to tell if there are black circles or not.
Finally, I have also included some parts for special purposes. You will encounter these parts frequently, so please keep them in mind while you are at it.
I will post these tables on the blog, so please bookmark them so that you can check them anytime.

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