Source: https://mokxi.com/boards/atmega328p Updated: 2026-10-26 Board # ATmega328P simulator, an Arduino on a breadboard The ATmega328P is the Uno’s chip on its own, in a 28-pin DIP that pushes into a breadboard. Mokxi has both builds the tutorials wire: 16 MHz from a crystal, which runs the Uno’s programs, and 8 MHz from the internal clock, which frees pins 9 and 10. Wire VCC to a supply, or nothing runs, as on the bench. Start building free - 6 peripheral areas modeled - 2 projects ready to run - Real time on your own machine Click to open it in the editor The board is running real firmware right now. Click it to open the circuit in the editor. The model ## What is modeled Taken from the board's own contract document and put in plain words, with what is missing beside it. ### Modeled Core Every ATmega328P mnemonic with datasheet cycle counts, at exactly 16 MHz or exactly 8 MHz Timers Three, in every waveform mode, with hardware PWM on pins 3, 5, 6, 9, 10 and 11 USART0 Wired to the serial monitor, paced at the baud rate you set ADC A0 to A5 on PC0 to PC5, ten bits Supply The chip runs only while VCC is on a supply of 1.8 V or more; without one every pin lets go The package All 28 pins in package order; pins 9 and 10 are the crystal’s on one build and PB6 and PB7 on the other ### Not modeled - The crystal and its two capacitors. They are not parts, and the clock is the build’s whether or not a crystal is wired. - The internal oscillator’s error: the 8 MHz here is exact. And the pins swing to 5 V whatever VCC is, so a chip on 3.3 V is not modeled as one. - AVCC and AREF are not checked, and there is no on-board LED, because there is no board. - Fuses and burning a bootloader. Each build starts with its clock set. Start here ## Open one and press Run Each of these opens in the editor exactly as it is drawn here. Projects ## Every built-in project on the ATmega328P Each has its own page with the circuit running, the code and a parts list. - ATmega328P on a breadboard Beginner Libraries ## Arduino libraries that compile as they are Paste a tutorial that includes one of these and it builds. For any other library, the build names the Mokxi header that does the same job. Servo.h attach, write, writeMicroseconds, read, detach, on any pin Wire.h I2C as a master; Wire.begin() puts it on PC4 (SDA, A4) and PC5 (SCL, A5) SPI.h transfer and transactions, on the board’s usual SPI pins EEPROM.h read, write, update, get, put and EEPROM[i], kept in the chip’s own 1 KB EEPROM LiquidCrystal_I2C.h the 16x2 LCD behind its I2C backpack Adafruit_GFX.h and Adafruit_SSD1306.h the 128x64 I2C OLED: text, pixels, lines, rectangles, circles, triangles and bitmaps Adafruit_NeoPixel.h WS2812 strips and panels DHT.h the DHT11 and DHT22: temperature, humidity and the heat index, as floats you can print And 15 more, 23 in all: OneWire.h and DallasTemperature.h ; Adafruit_BME280.h, Adafruit_BMP280.h and SparkFunBME280.h ; RTClib.h ; Adafruit_SHT31.h ; Adafruit_PCF8591.h ; Adafruit_ADXL345_U.h ; LedControl.h ; Adafruit_LEDBackpack.h ; Adafruit_TCS34725.h ; Adafruit_SGP30.h ; Adafruit_INA219.h ; Adafruit_ADS1X15.h ; Adafruit_MCP23X17.h ; Bounce2.h ; HX711.h . Learn ## Tutorials that use this board Each one ends in a running circuit, on this same board. - The ATmega328P pinout: package pins, port names and Uno numbers ## Questions Is it free? Yes. Every board and every part is on the free plan, with no account needed. Why does nothing happen? Check the supply first. The chip is not a board, so it has no supply of its own: wire VCC and AVCC to 5 V and both GND pins to ground. Without a supply on VCC every pin lets go, here as on the bench. Do I need the crystal? On a real 16 MHz chip, yes: a crystal between pins 9 and 10, with a 22 pF capacitor from each to ground. In Mokxi the crystal is not a part, and the chip runs at 16 MHz without one. The 8 MHz build needs none anywhere. How do I program a real one? With a programmer, such as a USBasp or an Uno running Arduino as ISP, or through a USB serial adapter if the chip has the Uno’s bootloader. The 8 MHz chip needs its fuses set once first: pick MiniCore’s ATmega328 with the internal 8 MHz clock and burn the bootloader. Also here ## The other boards Every one of these runs today, and every one is free. ESP32-C3-DevKitM-1 A RISC-V chip at 160 MHz, on the real memory map. Open the board page Arduino Uno R3 The classic Arduino, with an ATmega328P running at 16 MHz. Open the board page Arduino Nano The Uno’s chip on a small board that fits a breadboard. Open the board page Arduino Mega 2560 The big Arduino, with 54 digital pins and four serial ports. Open the board page Arduino Leonardo An Uno-shaped board whose chip does its own USB serial. Open the board page ESP32-C6-DevKitC-1 A second RISC-V board, with 31 pins and simulated WiFi. Open the board page ESP32 DevKit V1 The classic ESP32 at 240 MHz, with simulated WiFi. Open the board page ESP32-S3-DevKitC-1 The ESP32-S3 at 240 MHz, with USB serial and an RGB LED. Open the board page All 39 boards ## Try it on your own firmware What you build here runs on the board on your desk, unchanged. Nothing to install and no account needed. Start building free Open the editor