llms.txt
# Mokxi
> Mokxi is a free electronics and microcontroller simulator that runs in your web browser. You wire a circuit on a breadboard, write the firmware in C++ as you would for the real board, and press Run: the microcontroller and the circuit are simulated together, in real time, on your own computer. There is nothing to install and no account is needed to start.
Updated 2026-10-20. Made by Mokxi LLC, Colorado Springs, Colorado, USA ([about](https://mokxi.com/about)).
Key facts, each stated on the pages linked below:
- Free: every board, every part and the whole simulator are on the free plan, with no card. Paid plans add private projects, tools and classroom features: Hobby is $5 a month or $50 a year, Pro is $10 a month or $100 a year, Pro for work is $20 a seat a month, for teams, Teacher is $14 a month or $129 a year for a teacher and 40 students, schools and universities with more than 40 students get a written quote, and students with a school email get Pro for $5 a month or $50 a year. Prices are in US dollars. A Free account can try Pro free for seven days, once, with no card ([pricing](https://mokxi.com/pricing)).
- The Free plan has no time limit on simulating, and a free account saves 10 projects; the ones lessons make do not count. Projects on Free are public: anyone can find them. Private and link-only projects come with the paid plans, from Hobby up. Students in a class and children under 13 are always private, free. The Circuit Doctor checks wiring and code on every plan; on Free its AI gives 2 explanations a day of what it found ([pricing](https://mokxi.com/pricing)).
- Runs in the browser, including on school Chromebooks and on phones, because the simulation runs on the device in front of you ([students](https://mokxi.com/students), [teachers](https://mokxi.com/teachers)).
- 32 boards: ESP32-C3, Arduino Uno, Arduino Nano, Arduino Mega 2560, Arduino Leonardo, ESP32-C6, Raspberry Pi Pico, Raspberry Pi Pico W, Seeed XIAO SAMD21, STM32F411 Black Pill, STM32 Blue Pill, Arduino Uno R4 Minima, ESP32, ESP32-S3, ESP8266 NodeMCU, ATtiny85, Arduino Pro Mini, Arduino Micro, SparkFun Pro Micro, Wemos D1 mini, ESP-01, Seeed XIAO ESP32-C3, Seeed XIAO ESP32-C6, ESP32-DevKitC V4, Wemos LOLIN32 Lite, Seeed XIAO ESP32-S3, Arduino Nano ESP32, Arduino Nano RP2040 Connect, ESP32-C3 SuperMini, Arduino Uno R4 WiFi, BBC micro:bit V2, Arduino Pro Mini 3.3 V ([all boards](https://mokxi.com/boards)). Your own sketch compiles in the browser for every one of them; each board page says what runs and what is not modeled.
- Parts: more than 260, from breadboards, LEDs, resistors, 74HC logic and the NE555 to sensors, displays, motors, servos, robot parts (a 2WD car chassis, a line tracker, a robot arm, servo and stepper drivers) and bench instruments such as an oscilloscope, a multimeter and a four-channel logic analyzer ([parts](https://mokxi.com/parts)).
- Tools in the editor: a serial monitor that talks both ways, a serial plotter that reads the Arduino IDE plotter format, the logic analyzer with UART, I2C and SPI decoding, and a debugger that stops a board on a line of your code ([serial monitor and logic analyzer](https://mokxi.com/learn/arduino-simulator-serial-monitor-logic-analyzer)).
- Analog and SPICE: the analog parts of a live circuit are solved by nodal analysis with real device models, and Run a SPICE deck, in the editor, runs a SPICE netlist (operating point, transient, AC, DC sweeps, transfer function, noise and measurements, with subcircuits and model cards) on an engine checked against ngspice on 42 benchmark circuits. It does not run BSIM MOSFET models, XSPICE devices or distortion analysis ([SPICE in the browser](https://mokxi.com/learn/online-spice-simulator)).
- Digital logic: a logic gate simulator, and a learning path that starts with one NAND gate and ends with a small computer you build from your own chips ([build a computer from NAND gates](https://mokxi.com/learn/build-a-computer-from-nand-gates)).
- For classes: rosters, assignments, a teacher dashboard and checks that grade submissions, on Pro and Teacher; a free 30-day class trial; and a free 12-week Arduino course ([teachers](https://mokxi.com/teachers), [curriculum](https://mokxi.com/curriculum)).
- Made for students, teachers and hobbyists everywhere, with US schools in mind. Written in English; the language menu opens any page through Google Translate. Prices are set in US dollars, the pricing page shows an estimate in the local currency for many countries, and Stripe Checkout shows the exact amount before payment.
- To send somebody straight to a circuit that runs, link the simulator page for the topic (for example [the op-amp simulator](https://mokxi.com/op-amp-simulator) or [the breadboard simulator](https://mokxi.com/breadboard-simulator)) or [the online circuit simulator](https://mokxi.com/online-circuit-simulator). Each opens a circuit that runs with no account and no sign-in, and so does the editor at mokxi.com/app/. Trying a circuit never needs the sign-in page.
- Every page listed below also has a plain Markdown copy at the same address with `.md` added (for example https://mokxi.com/learn/ohms-law.md). Cite the page itself.
- Every board, part, example project, kit, guide and Arduino library is also described as one small Markdown file in an Open Knowledge Format bundle at https://mokxi.com/okf/ (each file names the page to link in its `resource` field; the whole bundle is https://mokxi.com/okf/mokxi-okf.tar.gz).
## Common questions, and the page that answers each
- [Is there a free online Arduino simulator?](https://mokxi.com/arduino-simulator): Simulate an Arduino Uno, Nano, Mega or Uno R4 free in your browser: a real compiler, a real breadboard, analog parts and more than 100 libraries. No install.
- [Can I simulate an ESP32 in the browser?](https://mokxi.com/esp32-simulator): Simulate an ESP32 DevKit, ESP32-S3, C3 or C6 free in your browser, with simulated WiFi, a real breadboard and your sketch compiled in the tab.
- [Is there a Raspberry Pi Pico simulator online?](https://mokxi.com/raspberry-pi-pico-simulator): Simulate a Raspberry Pi Pico, Pico W or Nano RP2040 Connect: our own Cortex-M0+ core at 125 MHz, GPIO, timers and PWM. Free, nothing to install.
- [Is there an STM32 simulator online?](https://mokxi.com/stm32-simulator): Simulate an STM32F411 Black Pill or STM32F103 Blue Pill in your browser, on our own Cortex-M cores with the real register maps. Free, no install.
- [Can I compile and check Arduino code online?](https://mokxi.com/online-arduino-compiler): Compile Arduino code online, free: a real clang builds your sketch in the browser and runs it on a simulated board. No install, no account, no compile limit.
- [How can I simulate an Arduino project without hardware?](https://mokxi.com/learn/simulate-arduino-without-hardware): Test a sketch and a wiring plan before any part arrives: build the circuit, write the code and press Run, all in a browser tab, in the example below.
- [Which Arduino projects are good for beginners?](https://mokxi.com/learn/arduino-projects-for-beginners): Twelve Arduino projects for beginners, in the order that builds skills, each running in your browser with the wiring and code. Free, no kit needed.
- [Can I simulate Arduino on a Chromebook?](https://mokxi.com/learn/arduino-simulator-chromebook): Write and run Arduino code on a school Chromebook with nothing to install. What works in the browser, what needs real hardware, and how to start.
- [Is there an Arduino simulator for Mac?](https://mokxi.com/learn/arduino-simulator-mac): Run Arduino and ESP32 code on a Mac with nothing to install: what works in Safari and Chrome, which desktop simulators run on macOS, and how to reach a board.
- [Is there an Arduino simulator with a serial monitor and a logic analyzer?](https://mokxi.com/learn/arduino-simulator-serial-monitor-logic-analyzer): Mokxi is a free Arduino simulator in your browser with a two-way serial monitor, a serial plotter, a 4-channel logic analyzer, a scope and a debugger.
- [What is a free Arduino simulator for a classroom?](https://mokxi.com/teachers): Teach Arduino and electronics on school Chromebooks with a live simulator, class rosters, starter projects, checks, submissions and a twelve-week curriculum.
- [What is a good free simulator for students?](https://mokxi.com/learn/free-arduino-simulator-for-students): A free Arduino simulator for students: every board and part, no account needed to start, and Pro at half price with a school email, including .edu.co.
- [How do I wire a servo to an Arduino?](https://mokxi.com/learn/arduino-servo-motor): Wire an SG90 servo and a potentiometer to an Arduino Uno and move the horn with the knob. Runs in your browser, with the code and the pulse explained.
- [How do I control a servo with an ESP32?](https://mokxi.com/learn/esp32-servo-motor): Wire an SG90 servo to an ESP32 and sweep it with a 50 Hz LEDC signal on GPIO 4. Runs free in your browser, with the wiring and the code explained.
- [How do I read a button on a Raspberry Pi Pico?](https://mokxi.com/learn/raspberry-pi-pico-button): Wire a pushbutton to a Raspberry Pi Pico with the internal pull-up and light the LED while it is held. Runs free in your browser, code explained.
- [How do I wire an ultrasonic sensor to an Arduino?](https://mokxi.com/learn/arduino-ultrasonic-sensor): Measure distance with an HC-SR04 and an Arduino Uno, then turn it into a parking sensor that beeps faster as you get closer. Runs in your browser.
- [How do I wire an I2C LCD to an Arduino?](https://mokxi.com/learn/arduino-lcd-i2c): Drive a 16x2 LCD with an I2C backpack from an Arduino Uno on four wires. A running thermometer, the LiquidCrystal_I2C code, and the common faults.
- [How do I wire a 16x2 LCD to an Arduino without I2C?](https://mokxi.com/learn/arduino-lcd-16x2): Wire a 16x2 LCD to an Arduino Uno on six pins with the LiquidCrystal library. Hello world runs live in your browser, with the fixes for a blank screen.
- [How do I use an SSD1306 OLED display with an Arduino?](https://mokxi.com/learn/arduino-oled-display): Draw text and shapes on a 128x64 SSD1306 OLED from an Arduino Uno over I2C. Running circuit, the Adafruit code, and why an OLED stays black.
- [How do I read a DHT22 or DHT11 with an Arduino?](https://mokxi.com/learn/arduino-dht22): Read a DHT22 or DHT11 with an Arduino Uno and show it on an I2C LCD. Running circuits, the DHT library code, and why the first reading fails.
- [How do I drive NeoPixels (WS2812B) from an Arduino?](https://mokxi.com/learn/arduino-neopixel): Wire a WS2812B NeoPixel strip to an Arduino Uno and run a rainbow with the Adafruit_NeoPixel library. Live in your browser, with the mistakes that go dark.
- [How do I use a 4x4 keypad with an Arduino?](https://mokxi.com/learn/arduino-keypad): Scan a 4x4 membrane keypad with an Arduino Uno and build a code lock that clicks a relay. Running circuit, wiring, and the keypad scan explained.
- [How do I read an MPU6050 with an Arduino?](https://mokxi.com/learn/arduino-mpu6050): Wire an MPU6050 (GY-521) to an Arduino Uno over I2C, wake it, read it and turn gravity into a tilt angle. A running tilt meter with three lamps.
- [Why does my Arduino relay module work backwards or click at startup?](https://mokxi.com/learn/arduino-relay-module): Why a relay module turns on with LOW, clicks when the Arduino starts, or will not switch at all, with fixes you can try on a live relay board in your browser.
- [What is a Tinkercad Circuits alternative?](https://mokxi.com/vs/tinkercad): A Tinkercad Circuits alternative with ESP32, Pico and STM32 boards, real C++ and a class workflow. Where Mokxi fits, and where Tinkercad is still better.
- [How does Mokxi compare with Wokwi?](https://mokxi.com/vs/wokwi): Looking for a Wokwi alternative? Mokxi compiles in your browser, simulates analog parts and runs classes. See honestly where Wokwi is still the better pick.
- [How does Mokxi compare with SimulIDE?](https://mokxi.com/vs/simulide): SimulIDE is a free desktop simulator for PIC, AVR and Arduino circuits. Mokxi runs 32 boards in a browser tab with nothing to install.
- [How does Mokxi compare with Proteus?](https://mokxi.com/vs/proteus): Proteus is a paid, SPICE-accurate tool with PCB design; Mokxi is free and runs Arduino firmware in a browser. See where each one is the right answer.
- [Which Arduino simulators are there, compared?](https://mokxi.com/learn/arduino-simulators-compared): Fourteen Arduino, logic and SPICE simulators, compared for students, teachers and makers: class tools, boards, firmware, SPICE, price and setup.
- [What is the best ESP32 simulator?](https://mokxi.com/learn/best-esp32-simulator): Which simulators run an ESP32 in 2026, and which do not: Wokwi and Mokxi compared on chips, WiFi, languages, compiling, price and classes, with sources.
- [What are the alternatives to Tinkercad Circuits?](https://mokxi.com/learn/tinkercad-alternatives): Six alternatives to Tinkercad Circuits for Arduino and electronics, compared honestly: what each runs, what it costs, whether it needs an install or a login.
- [What is a good Wokwi alternative for a classroom?](https://mokxi.com/learn/wokwi-alternatives): Alternatives to Wokwi compared honestly: Mokxi for classes and analog parts, SimulIDE offline and open source, Tinkercad for beginners, Proteus for industry.
- [What is the best free logic gate simulator?](https://mokxi.com/learn/best-logic-gate-simulator): Free logic gate simulators compared: CircuitVerse, Logisim-evolution, Digital, Falstad and Mokxi, on browser or desktop, class tools, HDL and real chips.
- [What is the best free circuit simulator?](https://mokxi.com/learn/best-free-circuit-simulator): Free circuit simulators compared: Falstad, LTspice, Qucs-S, EveryCircuit, Tinkercad, CircuitVerse and Mokxi, for students, hobbyists and SPICE work.
- [What does Science Olympiad Circuit Lab Division C cover beyond Division B?](https://mokxi.com/learn/circuit-lab-division-c): A high school guide to Circuit Lab Division C: two-source networks, Thevenin, RC and RL, AC and resonance, transistors and op-amps, each on a live circuit.
- [Is there a Circuit Lab cheat sheet with worked examples?](https://mokxi.com/learn/circuit-lab-cheat-sheet): A Circuit Lab cheat sheet to copy into your own notes: Ohm, power, dividers, Kirchhoff, RC, reactance, resonance and part codes, each with a worked example.
- [Can I simulate an I2C bus and see it decoded?](https://mokxi.com/i2c-simulator): An Arduino reads a DS3231 clock over I2C while a logic analyzer decodes every address, byte and acknowledge. A free online I2C simulator, no install.
- [Is there a free online oscilloscope simulator?](https://mokxi.com/oscilloscope-simulator): A free online oscilloscope simulator: two channels on a live circuit, a signal generator, triggers, cursors and an FFT. Runs in your browser, no install.
- [Can I practice on a virtual multimeter?](https://mokxi.com/multimeter-simulator): A free online multimeter simulator: volts, amps, ohms, continuity, diode and capacitance on a real breadboard circuit, with a fuse that blows. No install.
- [Can I simulate a series and parallel circuit with a battery?](https://mokxi.com/series-parallel-circuit-simulator): A free series and parallel circuit simulator: a 9 V battery, three resistors and two meters on a breadboard. Read the current and voltage split. No install.
- [Is there a Wheatstone bridge simulator online?](https://mokxi.com/wheatstone-bridge-simulator): A free online Wheatstone bridge simulator: four arms from 5 V, a thermistor as the unknown and a meter that reads zero at balance. Runs in your browser.
- [Is there a free online PID simulator I can tune?](https://mokxi.com/pid-simulator): A free online PID simulator: an Arduino balances a two-wheel robot and three knobs tune Kp, Ki and Kd live. Turn a term off and watch it fall. No install.
- [Can I simulate a solar panel and find its maximum power point?](https://mokxi.com/solar-panel-simulator): A free online solar panel simulator: a 6 V 1 W panel on a load, with meters on its current and voltage. Drag the sunlight and find its maximum power point.
- [Is there an AC circuit simulator with RMS meters?](https://mokxi.com/ac-circuit-simulator): A free online AC circuit simulator: a 60 Hz sine through a resistor and a capacitor, with true RMS meters and a scope. Change the frequency. No install.
- [Can I check a Thevenin equivalent against the real circuit?](https://mokxi.com/thevenin-simulator): A free online Thevenin theorem simulator: a 12 V network beside its 8.16 V, 5.40 k equivalent, each on the same load, and both meters agree. No install.
- [Can I simulate two Arduinos talking over nRF24L01 radios?](https://mokxi.com/nrf24l01-simulator): A free online nRF24L01 simulator: two Arduino Unos send packets with the RF24 library and read the acknowledgment. Press a button, watch the other answer.
- [Can I test HC-05 Bluetooth code without pairing a phone?](https://mokxi.com/bluetooth-module-simulator): A free online HC-05 Bluetooth module simulator: type commands where a phone app would, and an Arduino Uno switches a lamp. Test the sketch before pairing.
- [What does "was not declared in this scope" mean in Arduino?](https://mokxi.com/learn/arduino-was-not-declared-in-this-scope): Why Arduino says a name "was not declared in this scope": a typo, braces, a missing #include, a name from another board, the order. Each cause, and its fix.
- [How do I fix avrdude stk500_getsync() not in sync?](https://mokxi.com/learn/avrdude-stk500-getsync-not-in-sync): What avrdude's "stk500_getsync(): not in sync" means when an Arduino upload fails, and a checklist: port, board, bootloader, pins 0 and 1, cable, reset.
- [Which ESP32 DevKit V1 pins are safe to use, and which are strapping pins?](https://mokxi.com/learn/esp32-devkit-v1-pinout): Every pin on the 30-pin ESP32 DevKit V1: GPIO numbers, ADC1 and ADC2, I2C and SPI defaults, strapping pins, input-only pins, the LED and power limits.
- [What GPIO numbers are D0 to D8 on a NodeMCU or a D1 mini?](https://mokxi.com/learn/nodemcu-pinout): The NodeMCU ESP8266 pinout: D0 to D8 as GPIO numbers, the flash pins never to use, I2C and SPI, A0, VIN and 3V3, both LEDs, and the pins that must boot right.
- [Which Arduino Nano pins are PWM, I2C and SPI?](https://mokxi.com/learn/arduino-nano-pinout): The Arduino Nano pinout: every pin with its ATmega328P port, PWM pins and timers, I2C, SPI and ICSP, the interrupt pins, A6 and A7, VIN and the limits.
- [Which Raspberry Pi Pico pins share a PWM slice?](https://mokxi.com/learn/raspberry-pi-pico-pinout): The Raspberry Pi Pico pinout: all 40 pins, the PWM slice on each GPIO, ADC0 to ADC2, the I2C, SPI and UART defaults, VBUS, VSYS, 3V3 and the LED on GP25.
- [Why does GP25 not light the LED on a Raspberry Pi Pico W?](https://mokxi.com/learn/raspberry-pi-pico-w-pinout): The Raspberry Pi Pico W pinout: the Pico’s 40 pins, and what differs. The LED on the CYW43439, GP23, GP24, GP25 and GP29, VSYS and VBUS sense.
- [Which STM32 Blue Pill pins are 5 V tolerant?](https://mokxi.com/learn/stm32-blue-pill-pinout): The STM32 Blue Pill pinout: every STM32F103C8 pin, which ones are 5 V tolerant, the ADC, PWM, I2C, SPI and Serial pins, PC13’s LED on LOW and the BOOT jumpers.
- [What are the Pro Micro pin names in QMK?](https://mokxi.com/learn/pro-micro-pinout): The SparkFun Pro Micro pinout: every pin with its ATmega32U4 port, as QMK names it, PWM, I2C, Serial1, the analog pins, the RX and TX LEDs, RAW and VCC.
- [Which Arduino Mega 2560 pins are PWM, Serial1 to Serial3, I2C and SPI?](https://mokxi.com/learn/arduino-mega-pinout): The Arduino Mega 2560 pinout: all 70 pins with their ATmega2560 ports, the 15 PWM pins and timers, four serial ports, interrupts, I2C and SPI.
- [What does an I2C scanner print, and why does mine find nothing?](https://mokxi.com/learn/i2c-scanner): An I2C scanner sketch for Arduino and ESP32 t
