1.Schematic Capture

Objective

In this section, you will get familiarized with the schematic editor then complete an exercise which will have you open the schematic editor, place the logical symbols for your components, and wire them together to form a complete circuit.

Getting to know the Schematic Editor

This section is packed with information! As you go through it, just familiarize yourself with KiCad. In the next section you'll put it into practice and you can always come back to reference this overview.

Opening the Schematic Editor

The Schematic Editor is where logical symbols for components are placed and wired together to form a complete circuit. To open the editor, double-click on the .kicad_sch file in the project tree, or click the Schematic Editor button on the right side of the Project Manager window. See the image below for reference.

The Top Toolbar: Project Management and Checks

A. Zoom Buttons: These controls allow you to navigate the schematic canvas. You can zoom in, zoom out, redraw the view, or zoom to fit the entire schematic within your window.

B. ERC (Electrical Rules Checker): This function scans your schematic for logical electrical errors, such as missing power connections or pins that have been accidentally left unconnected.

C. Symbol Fields Table: This tool opens a spreadsheet view of all the components in your schematic. It is a highly efficient way to bulk-edit component values and assign physical footprints to all your parts in one centralized location.

D. Open PCB in Board Editor: This button transitions your workflow from the logical schematic capture stage directly into the physical PCB layout editor.

The Right Toolbar: Drafting and Wiring

1. Selection Tool: The default cursor. Use this to select, move, or modify any item already placed on the canvas.

2. Place Symbol: Opens the KiCad component library, allowing you to search for and place logical components like resistors, capacitors, and LEDs.

3. Add Power Symbol: A dedicated shortcut for placing power ports, such as VCC (voltage) and GND (ground).

4. Add Wire: The primary drafting tool. Use this to draw the electrical connections between the pins of your components.

5. No Connect Flag: Used to place a small "X" on a component pin. This explicitly tells the software that the pin is intentionally left blank, which prevents false errors when running the ERC.

6. Add Net Label: Allows you to assign a text name to a wire. Wires with the identical net label are logically connected in the software, even if a physical wire is not drawn between them.

7. Add Text: Allows you to place general notes, titles, or documentation directly onto the schematic canvas.

Excercise: Your first schematic

Remember Blinking LED? In this tutorial we will go through the schematic for blinking LED.

1. Abstracting the Metro Board

In KiCad, we do not need to draw the entire Metro M0 Express. Since we are only using Pin D13 and GND, we will represent the Metro board as a simple 2-pin connector. What this will look like is like any of the components found as a part of your sensor kit.

2. Placing the Components

Using the Place Symbols tool [keyboard shortcut: (A)], search for and place the following three items on your canvas:

Conn_01x02_Pin (This represents the connection to the Metro board)
R_US (Resistor)
LED (Light Emitting Diode)

Example shown on the right of the first component selected.

3. Wiring the Circuit

Using the Add Wire tool, recreate the loop from your physical breadboard:

Connect Pin 1 of the connector to either side of the Resistor.
Connect the other side of the Resistor to the Anode (flat back) of the LED.
Connect the Cathode (pointy front with a line) of the LED to Pin 2 of the connector.

The schematic should look like the one picture on the right.

Tip: To rotate a component click on it once and hit (R) on your keyboard.

What is the Electrical Rules Checker (ERC)

The Electrical Rules Checker (ERC) functions as an automated proofreader for your circuit design. In the same way that a word processor scans a document for spelling and grammar errors, the ERC scans your schematic for logical electrical mistakes.

While you are responsible for the design (deciding which components connect to where), the ERC verifies that the execution of that design does not violate fundamental electrical rules.

Why We Use It:

The ERC is a mandatory validation checkpoint before transitioning to the PCB layout phase. It is significantly easier to fix a missed wire connection on the digital schematic canvas than it is to cut traces and solder jumper wires onto a manufactured physical circuit board. Earning a "zero errors" report from the ERC provides confidence that the foundational logic of the board is structurally sound before you begin routing physical copper.

Step 4. Verifying the Circuit

Navigate to the top toolbar and click the ERC icon (the checklist with a red checkmark).
Click the Run ERC button in the dialog window.
The software will verify that all pins are connected. If the window returns zero errors, the logical design is complete, and you may save the file.

Tip: Don't forget to periodically save your work as you go by selecting File > Save or Ctrl + S.

This is what you should see after the previous step.

What the ERC Looks For:

Floating Pins: It flags any component pins that are completely unconnected. If a pin is intentionally left blank, you must explicitly mark it with the "No Connect Flag" tool (the blue X) so the ERC knows it was not simply forgotten.
Power Conflicts: It detects if two incompatible pins are wired together, such as two output pins driving the same line, or a power source shorted directly to ground.
Missing Power Connections: It alerts you if a component that requires power to function has not been properly connected to a voltage source.

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