What is Circuit Simulator?
Circuit Simulator is a free browser-based electronics bench where you wire a circuit, write firmware, and watch the two run together. Arduino Uno sketches execute on a cycle-accurate ATmega328P core and PIC16F886 programs run on a built-in engine, both with a source-level debugger, logic analyzer, and oscilloscope. Parts seat into a real breadboard, sensors answer with correct timing, and I2C displays show what your code actually sent. Nothing installs and no account is required.
Is Circuit Simulator free?
Yes, completely free. There is no account, no project limit, no watermark, and no paid tier. Projects stay in your browser until you export or share them yourself.
Which microcontrollers actually execute code?
Arduino Uno (ATmega328P) and PIC16F886 both execute real firmware in the browser with no server involved. ESP32 projects give you the circuit, source workspace, and wiring, and run firmware only when you connect the optional local companion service that provides ESP-IDF and QEMU.
How do I simulate an Arduino Uno online?
Choose the Arduino Uno target on the start screen, write or paste your sketch, wire parts to the board pins, then press Run. The built-in compiler handles common Arduino C++ sketches, and you can import a compiled .hex from the Arduino IDE for anything it does not cover.
Can I import my own compiled firmware?
Yes. Intel HEX files load directly for both ATmega328P and PIC16F886 targets, so firmware built with the Arduino IDE, avr-gcc, MPLAB, or GCBASIC runs against your circuit. You pick the target on import so the wrong processor never silently accepts a file.
Does Circuit Simulator upload my code or circuits?
No. Compilation, execution, and analysis all happen inside your browser tab. Your firmware and circuits never leave the device unless you export a file or copy a share link, and the only network activity is anonymous page analytics.
How does it compare to Tinkercad Circuits and Wokwi?
Tinkercad Circuits and Wokwi are both excellent and both want an account before you can save. Circuit Simulator asks for nothing, runs entirely client-side, and shares a whole project as a plain link. It also has transistors, MOSFETs and op-amps, which Wokwi users routinely leave for another tool, plus PIC16F886 and GCBASIC that neither offers, and a circuit checker that tells you when an LED has no resistor or a sensor has no pull-up. Their component libraries are still larger, so pick this when privacy, real electrical parts, and instant access matter most.
Can I share a circuit with someone else?
Yes. Copy share link puts the entire project, including the circuit, source files, and settings, into the URL itself. Anyone who opens that link gets an editable copy, and nothing is stored on a server.
Is this a SPICE simulator?
Not by itself. The built-in solver models digital nets, high-impedance states, and ADC voltages, which is what microcontroller work needs. You can export a standard SPICE netlist for device-level analysis, or connect a local ngspice service when current, noise, and tolerance actually matter.
Do Arduino libraries work?
Some do. Wire and LiquidCrystal_I2C compile and run today, so a pasted I2C LCD sketch works unchanged. Others are still being added, and anything the built-in compiler does not recognise can be built with the full toolchain and imported as Intel HEX, which always runs.
Does it work on a phone or tablet?
Yes. The layout adapts to small screens with a dedicated mobile workspace, though wiring dense circuits is easier with a mouse or trackpad on a larger display.