# Understanding electronics circuit diagram schematic symbols.

All electronic circuits are ultimately the connection of electrical components. Therefore, efficiently passing along the components needed, and how to make the electrical connections for a circuit is vital. This information is mostly passed along by the use of schematic diagrams. Schematic diagrams are basically blueprints for electrical circuits.

Looks like a good book.

## Main schematic diagram reading points.

Main circuit parts:

• Power source (battery, fixed or adjustable voltage supply)
• Load – Does something with the power provided by the supply. Such as, produce light, rotate a shaft, create heat, etc.
• Control – Often an on/off switch.

Sometimes added (circuit) analysis for educational purposes:

• Voltage across individual or multiple components.
• Current through an individual or series of components

Component selection and connection tips.

• Schematics only show what components to use and where they are connected to each other. Schematics do not show how to physically connect the components together. Circuit building is a separate skill.
• Resistors are extremely common and will usually have a number by/in them to indicate a suggested value in Ohms. Jagged lined or rectangles are probably the only symbols you will ever see for resistors. The same type of resistor may be referred to in the side notes as a protection, current limiting, voltage setting, etc. resistor. Those labels help you understand the resistor’s purpose in a particular circuit.
• Unless it is a precision circuit, it is usually perfectly fine to use a different value resistor as long as proper power dissipation for all parts of the circuit aren’t exceeded.
• Resistors usually only have the suggested wattage rating added to their schematic symbol if it is not 1/4W.
• Circuits tend to be drawn from left to right, and up to down. Positive side of the circuit is usually drawn more left and/or top, while the more negative side of the circuit is usually more to the bottom and/or right. Many circuits are dawn in a clockwise direction.
• Direct current circuits are usually given a zero volt reference point, typically called ground. Symbol for ground is usually 3 lines or triangle that gets narrower as they/it goes down. For direct current, ground is almost always the negative side of the power supply. If there are multiple DC power supplied involved, then you can be pretty sure that they all have their negative terminals directly connected.
• The positive side of the power supply(ies) is then usually indicated by a number indicating it’s voltage difference from the negative side. A 9 volt battery for instance, would be indicated by a battery.

### Basic components and connections

Basic electronic components alone can be used to make many education circuits.  Therefore, do not rush this part of the schematic learning process.

### Transistors

Transistors have probably the hardest component schematic symbol to understand. It doesn’t help that some people use a much different looking symbol for the same transistor type. Often there is a part number next to the schematic symbol for a transistor. Make sure to find the datasheet for that transistor

#### Integrated Circuit and op amp/comparator schematic basics

The physical appearance of integrated circuits (ICs) is often a rectangle or square with pins along the sides. There are also 3 terminal ICs that look like single transistor components. Op amp and comparator ICs however, are usually indicated by a triangle with at least 3 of the terminals shown. The inverting input (-), non inverting input (+) and output. The Op amp/comparator power, and other pins, are also often shown in the schematic diagram. Most other ICs are indicated by a square/rectangle with the part number in the middle. The connections are also indicated by a number for the pin used in that connection.