KiCad 7: My ATtiny412-SS USB Circuit Journey
I began by downloading KiCad from KiCad.org - it's free software, which is great.
After installation, I created a new project called "ATtinyusbsample" and opened the schematic editor.
For the resistors, I searched for "R" in the component library, placed them, and then set their values and footprints. copy and past
Decoupling Capacitor (C1),The 100nF capacitor was essential for stable operation:
- Searched for "C" in the component library
- Set its value to 100nF
- Selected an 0805 SMD footprint to match the resistors
- Connected it between VCC and GND directly near the microcontroller to filter power supply noise
The Zener diodes were important for USB protection
- Searched for "D_Zener" in the component library
- Placed two of them on the schematic
- Set their values to 3.6V
- Selected SOD-323 footprints for D1 and D2 (the USB protection diodes)
Used an 0805 LED footprint for D3 (which serves as an indicator)
- Connected D3 to one of the ATtiny's I/O pins through a resistor to serve as a status LED
Header Pins (J1, J2) (For programming and expansion:)
- Searched for "Conn_01x04" 4 pin header j1and j2
- Placed them on the schematic
- Connected J1 to the programming pins of the ATtiny Connected J2 to the remaining I/O pins and power
Connecting Everything Together
- After placing all components, I carefully connected them following same other USB Digispark reference design: The USB connector's D+ and D- lines connect to the ATtiny through 68Ω resistors The 3.6V Zener diodes (D1, D2) are connected to these lines for protection The 1.5kΩ pull-up resistor (R4) is connected to the D- line as required by the USB standard The 330Ω resistor (R3) is connected to one of the ATtiny's pins and the LED The decoupling capacitor is placed directly between VCC and GND All components share a common ground
Creating Custom Parts
- For the USB connector, I needed to create both a custom symbol and footprint. In the symbol editor, I: Created a new library called "my custom symbol Library" Made a new symbol named "PCB USB Connector" Added four pins with specific properties: Pin 1: VCC (power input) Pin 2: D+ (bidirectional) Pin 3: D- (bidirectional) Pin 4: GND (power input)
- Drew a rectangle and labeled it "USB" In the footprint editor, I created a matching footprint with: Four SMD pads with specific dimensions: Pads 1 & 4: 7mm × 2mm Pads 2 & 3: 6mm × 1.5mm Positioned at -3.75mm, -1mm, 1mm, and 3.75mm Added silkscreen text reading "USB" Created a 5mm keep-out zone to prevent other components from being placed too close
After completing the schematic, I generated the PCB layout using the "Update PCB from Schematic" tool. First, I defined a board outline of 14mm × 12.2mm using the edge cuts layer. Then I arranged all the components within this outline, keeping in mind: The USB connector needed to be positioned at the edge The ATtiny needed enough space for all its connections Components should be spaced to make soldering easier
I connected everything with tracks, using vias where I needed to change layers, but it took me a long time to do it.
I searched on how to do the autoroute then go through the description
went to plugin and searched for freerouting
Back to PCB editor and tool,then External plugins clicked
the result was fast and good campare to mine
my 3d view front
my 3d view back
KiCad: My XIAO RP2040 Interface Board Journey
I started by set up the Fablab library using these steps:
- Downloaded the library from Fablab kicad library
- Located the zip folder in my downloads and extracted it to my documents folder
- Opened KiCad and went to "Preferences / Manage Symbol Libraries"
- Added fab.kicad_sym as a symbol library
- Went to "Preferences / Manage Footprint Libraries"
- Added fab.pretty as a footprint library
- Went to "Preferences / Configure Paths" and added new environment variable "FAB" pointing to the library location
Adding the XIAO RP2040 Module (M1)
- For the main microcontroller module, I added the XIAO form fab libraries
Creating the custom symbol for the XIAO RP2040 module with all the necessary pins.
Adding Pin for Interfaces
- Searched for "fab:PinHeader_01x06" for the 4 and 6-pin headers
- Placed several connectors on the left and bottom sides of the schematic
- Named them according to their functions (I2C, UART, SPI, GPIO)
- Added power and ground connections to each connector as needed
Placing the connector symbols and assigning appropriate pins for each interface.
Push Button (SW1) and LED Circuit (D1)
- Searched for "SW_Push" in the component library for the tactile switch
- Connected it between the SWITCH+D2 pin and GND
- Added an LED with two resistors (R1 and R2) to limit current
- Connected the LED circuit to the LED+D1 pin of the XIAO module
Adding the user interface components - push button and LED with current-limiting resistors.
Connecting Everything Together
- Connected all power pins to the PWR_3V3 power net
- Connected all ground pins to the GND net
- Connected the I2C pins (SDA+D4, SCL+D5) to their respective connectors
- Connected the UART pins (TX+D6, RX/CSN+D7) to their connectors
- Connected the SPI pins (MISO+D9, MOSI+D10, SCK+D8) to their connectors
The completed schematic with all components properly connected according to the design requirements.
bcp editor with all connection connected
PCB Layout
- After completing the schematic, I generated the PCB layout using the "Update PCB from Schematic" tool
- Defined a board outline of 50mm × 40mm using the edge cuts layer
- Positioned the XIAO RP2040 module in the center of the board
- Arranged the connectors along the edges for easy access
- Placed the LED and push button on the right side for user interaction
Final Result
- Ran the Design Rules Check (DRC) to ensure no errors
- Verified all connections matched the schematic
- Generated 3D views to visualize the final board
My 3D view front.