Meet EWsim: Free Browser-Based Circuit Simulator

It handles both analog and digital circuits on a single canvas. Building is deliberately simple: drag a component onto the sheet, hover over a pin, and draw a wire. The wiring is meant to stay out of your way so you can focus on the circuit.

Component library

The library covers what you actually reach for in real designs. Many blocks expand into families:

• Sources: DC and AC voltage sources, DC current source, wave/function generator, battery, Vcc, and ground.
• Passives: resistors (including DIP arrays), potentiometers and variable resistors, capacitors, electrolytic and variable capacitors, inductors and variable inductors, and transformers.
• Active devices: diodes, Zener diodes, SCR, diac, triac, BJTs, MOSFETs, JFETs, op-amps, comparators, analog multiplexers, voltage regulators, and optocouplers.
• Switches and inputs: push-buttons, toggle switches, DIP switches, relays, keypads, touch pads, dual-axis joysticks, and rotary encoders.
• Digital blocks: digital I/O, logic gates, combinational and sequential blocks, memory, and the 74xx series.
• Displays and outputs: LED modules, motors and servos, and a broad display set — character LCDs (HD44780, I2C LCD), OLED (I2C/SPI), graphical LCDs (128×64, Nokia 5110), and TFT color displays (ST7735, ST7789, GC9A01A).
• Sensors and modules: ultrasonic, DHT temperature/humidity, DS18B20 and DS1621, DS1307 RTC, SD card reader, ESP01, ADC/DAC, LDR, thermistor, RTD, strain gauge, the 555 timer, and I²C/SPI/parallel digital potentiometers.

You measure and probe the running circuit with built-in instruments: a probe, voltmeter, ammeter, frequency meter, oscilloscope, logic analyzer, and a serial terminal. Together, these cover DC measurement, waveform capture, digital timing analysis, and UART interaction without leaving the browser.

EWsim simulates analog and digital circuits together, in real time. Voltages, currents, and signals update live as the circuit runs.

This makes it a strong tool for learning, prototyping, and driving a microcontroller against real peripherals.

It is not a SPICE-grade simulator. It uses simplified component models, does not do professional level analyses like DC/AC sweeps, frequency and noise analysis, or Monte Carlo. Simulation is mainly focused on how a circuit behaves and works; it is focused on simplicity.

Try this example- click here

EWsim runs firmware on virtual microcontrollers across four families: Arduino, AVR, PIC, and 8051. It has a built-in code editor and compiler, so you write your code, compile, and simulate in the same place. Compilation runs server-side, and every supported controller can also be simulated directly from a pre-built .hex file if you prefer to bring your own build.

EWsim can simulate multiple controllers simultaneously.

The toolchains behind each family:

• AVR- ATmega & ATTiny Controllers- AVR-GCC, simulated with SimAVR.
• Arduino (UNO, MEGA, NANO)- the Arduino CLI toolchain.
• 8051- a standard open-source compiler.
• PIC (PIC10F, PIC12F, PIC16F)- an industry-standard C compiler.

ESP32 and ARM support: development is in progress, with QEMU integration.

For AVR and Arduino, EWsim gives you full source-and-Controller visibility into the running MCU. You can set breakpoints, single-step through execution, and inspect the entire chip state as you go: every register, the status flags, the program counter, RAM, Flash, EEPROM, and a live disassembly view. 

Each entry in the watch table shows its address, name, value, and type — the kind of low-level insight normally reserved for a hardware debugger, running entirely in your browser. Debugging support for the remaining families is on the roadmap.

EWsim is the most capable free, browser-based simulator that combines mixed-signal analog+digital, firmware execution across multiple MCU families (AVR, PIC, 8051, Arduino) with register-level debugging.

EWsim is free and runs entirely in the browser. Whether you are a student learning your first circuit, or developer prototyping an idea, or an engineer sketching out firmware and HDL, everything above is available the moment you open it.

EWsim.io wouldn't exist without the open-source electronics simulation community. Our simulation core is built on open-source tools, emulators, and compilers — full credit to the projects and authors that made this possible.

Written by-
	Ganesh Khomane (Co-Founder EWskills)
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