Attiny412 addressable

Cursed PCB

Cursed PCB is a programmable light board with an ATtiny412 microcontroller, four individually addressable RGB LEDs, onboard USB-C power, and an onboard CH340 SerialUPDI programmer. Plug it into a computer, install the ATtiny board support in Arduino IDE, and upload your own light patterns.

Quick links: LED example · megaTinyCore documentation

Repository contents

• examples/LED_example/LED_example.ino — ready-to-upload LED animations and optional button support
• attiny412_addressable.kicad_sch — KiCad schematic
• attiny412_addressable.kicad_pcb — KiCad PCB layout
• attiny412_addressable.kicad_pro — KiCad project settings
• 3d/attiny412_addressable_no_pin_headers.step — STEP assembly without the 1×6 and 1×3 pin headers
• 3d/attiny412_addressable_no_pin_headers.wrl — VRML assembly without the 1×6 and 1×3 pin headers

The 3D exports include the PCB and modeled onboard components. J2 (the 1×6 GPIO header) and J3 (the 1×3 UPDI/power header) are intentionally unpopulated.

What you need

• The Cursed PCB
• A USB-C data cable (some charging-only cables cannot upload code)
• Arduino IDE
• The LED_example sketch in this repository

No separate LED library download is required. The tinyNeoPixel_Static library used by the example is included with megaTinyCore.

1. Install ATtiny412 support

The ATtiny412 is not included in Arduino IDE by default. Install the megaTinyCore board package:

1. Open Arduino IDE.

2. Open File → Preferences. On macOS, open Arduino IDE → Settings.

3. Add this URL to Additional Boards Manager URLs:

   http://drazzy.com/package_drazzy.com_index.json

   If another URL is already present, use the button beside the field and add this URL on a new line.

4. Open Tools → Board → Boards Manager.

5. Search for megaTinyCore.

6. Install the newest version of megaTinyCore by Spence Konde.

The package includes the compiler, upload utility, and tinyNeoPixel libraries needed by this board.

2. Connect and configure the board

Connect the board directly to the computer with a USB-C data cable. The power LED should turn on and a new serial port should appear in Arduino IDE.

Select these settings under Tools:

Choose the board entry without “w/Optiboot.” This board programs the ATtiny412 directly over UPDI and does not need a bootloader.

The onboard CH340 connection is dedicated to UPDI programming. It is not connected to the ATtiny412's normal UART pins, so Arduino Serial Monitor will not display Serial.print() output through this USB-C connection. PA6/TX and PA7/RX remain available on the six-pin header for an external serial adapter.

3. Open and upload the example

1. Download or clone this repository.
2. Open examples/LED_example/LED_example.ino in Arduino IDE.
3. Compile with Sketch → Verify/Compile.
4. Upload with Sketch → Upload Using Programmer. The regular Upload button is not used for this UPDI setup.

After the upload finishes, the four LEDs run through red, green, blue, white, a rainbow sweep, and a moving white chase.

Optional mode button

The example supports an optional normally-open pushbutton connected between exposed pins 0 (PA6) and 2 (PA1). No external resistor is needed for this example: the sketch drives PA6 low and enables PA1's internal pull-up. Each press advances to the next animation.

If no button is connected, the example still works. It automatically shows the four solid colors and then continues with the rainbow sweep.

Programming the lights

The four onboard LEDs are SK6812MINI-E addressable RGB LEDs connected as one chain. The first LED's data input is connected to PA3, which megaTinyCore calls Arduino pin 4.

The important setup from the example is:

#include <tinyNeoPixel_Static.h>

constexpr uint8_t LED_PIN = PIN_PA3;  // Arduino pin 4
constexpr uint8_t NUM_LEDS = 4;

byte pixelData[NUM_LEDS * 3];
tinyNeoPixel leds(NUM_LEDS, LED_PIN, NEO_GRB, pixelData);

void setup() {
  pinMode(LED_PIN, OUTPUT);
  leds.setBrightness(20);              // 0 to 255
  leds.setPixelColor(0, 255, 0, 0);   // first LED: red
  leds.show();
}

tinyNeoPixel_Static keeps the LED buffer in a fixed array, which is helpful on the ATtiny412's limited memory. Set colors with setPixelColor(), then call show() to send the updated buffer to the LEDs. The LEDs use NEO_GRB byte order.

Keep the brightness modest while experimenting. Four LEDs at full white use much more current and can be uncomfortably bright.

Pinout

With the component side facing up and the USB-C connector at the bottom, the six-pin header reads left to right:

Arduino pin 4 / PA3 controls the onboard LEDs and is not on the six-pin header. PA0 / UPDI is reserved for programming.

The separate three-pin header is labeled UPDI, GND, VCC from top to bottom when the USB-C connector is at the bottom. For standalone external power, connect the supply's positive lead to VCC and its negative lead to GND. VCC feeds the onboard voltage regulator. UPDI is for advanced external programming; none of these pins are needed for normal USB-C programming.

Power and handling

• For normal use, power and program the board through USB-C.
• For standalone external power, connect the supply to VCC and GND on the side three-pin header. Do not power the board through the 5V pin.
• VCC passes through an onboard L78L05 linear regulator. It produces a fixed 5 V rail and is rated for a maximum of 100 mA total output current. The board itself and all four LEDs share that limit.
• The regulator needs approximately 7 V or more at VCC to maintain a regulated 5 V output. Keep VCC at or below the recommended 20 V maximum. The regulator IC's 30 V rating is an absolute maximum, not a recommended operating voltage. Higher input voltage creates more heat and reduces the practical current available.
• Regulator heat is approximately (VCC input − 5 V) × current. Keep external supply voltage and LED brightness as low as practical. Four LEDs at high or full-white brightness can exceed the regulator's 100 mA rating.
• Never connect an external supply to VCC while USB-C is connected. The two power sources are not isolated.
• The exposed 5V header pin is the regulator's output/board rail. It may be used only as a limited 5 V output when the board is properly powered; never feed an external supply into it.
• The board has exposed electronics. Prevent metal objects, conductive surfaces, and loose wires from shorting it.
• Disconnect power before changing wiring. Observe polarity when using external power.
• The LEDs can be very bright. Avoid staring directly at them at high brightness.

Troubleshooting

No serial port appears

• Try a known USB-C data cable and another USB port.
• Disconnect and reconnect the board while watching Tools → Port.
• If the computer does not recognize the onboard CH340 USB serial device, install the CH340 driver for your operating system.

Upload fails or reports “UPDI initialization failed”

• Confirm ATtiny412/402/212/202 (without Optiboot), BOD Voltage Level → 4.2V, and SerialUPDI - 230400 baud are selected.
• Use Sketch → Upload Using Programmer, not the regular Upload command.
• Close any serial monitor or other application using the board's port.
• Try SerialUPDI - SLOW: 57600 baud under Tools → Programmer.
• Unplug the board, reconnect it, reselect the port, and try again.

The sketch uploads but the LEDs stay dark

• Confirm the sketch uses four pixels, NEO_GRB, and LED pin PIN_PA3 or Arduino pin 4.
• Make sure the LED data pin is configured as OUTPUT when using tinyNeoPixel_Static.
• Increase setBrightness(20) slightly while testing, but do not start at full brightness.

The sketch is too large

The ATtiny412 has 4 KB of program flash and 256 bytes of SRAM. Prefer tinyNeoPixel_Static, avoid large strings and unnecessary libraries, and keep the pixel buffer at 4 × 3 = 12 bytes.

Hardware summary

• ATtiny412, 4 KB flash / 256 bytes SRAM
• Four SK6812MINI-E addressable RGB LEDs
• USB-C connector with onboard CH340 SerialUPDI programming
• Side VCC external-power input through an L78L05 regulator: recommended 20 V maximum input, fixed 5 V output, 100 mA maximum total output
• Four exposed GPIO pins, including I²C SDA/SCL
• Approximately 58 mm × 29.5 mm
• Four 2.2 mm mounting holes

For deeper ATtiny and library information, see the official megaTinyCore installation guide, megaTinyCore reference, and tinyNeoPixel reference.