Free tutorials and guides covering digital logic, analog circuits, and practical electronics. Build real circuits as you learn.
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Click "Editor" in the navigation bar. You'll see an empty canvas with a component palette on the left side. Components are organized into categories: Logic Gates, I/O, Analog, and more.
Click a component in the palette to select it, then click on the canvas to place it. Click and drag between component pins to draw wires. The simulation runs automatically — toggle switches and watch outputs change in real time.
Digital circuits work with two voltage levels representing binary 1 (HIGH) and 0 (LOW). By combining logic gates, you can build circuits that perform any computation a computer can do.
Every digital circuit is built from a small set of fundamental gates. The AND gate outputs HIGH only when all inputs are HIGH. The OR gate outputs HIGH when any input is HIGH. The NOT gate (inverter) flips a signal: HIGH becomes LOW and vice versa.
From these three basic gates, you can derive all other gates: NAND (NOT + AND), NOR (NOT + OR), XOR (exclusive OR — HIGH when inputs differ), and XNOR (exclusive NOR — HIGH when inputs match). In fact, NAND gates alone are sufficient to build any digital circuit, which is why they are called "universal gates."
Combinational circuits produce outputs that depend only on current inputs (no memory). Common examples include:
Sequential circuits have memory — their outputs depend on both current inputs and past states. The basic building block is the flip-flop:
By connecting flip-flops together, you can build counters, shift registers, and finite state machines — the foundation of all computer processors.
Analog circuits deal with continuous voltage and current values. Understanding analog electronics is essential for power supply design, signal processing, sensor interfaces, and audio systems.
Ohm's Law (V = I × R) is the foundation of all circuit analysis. Voltage (V) equals current (I) times resistance (R). In Open Circuits, you can place a resistor between a voltage source and ground, then use the voltage/current probes to verify Ohm's Law directly.
Kirchhoff's Voltage Law (KVL) states that the sum of all voltages around a closed loop is zero. Kirchhoff's Current Law (KCL) states that the sum of currents entering a node equals the sum leaving. These laws are the basis for the Modified Nodal Analysis (MNA) algorithm that powers Open Circuits' analog simulator.
A voltage divider uses two resistors in series to produce an output voltage that is a fraction of the input. The output voltage is: Vout = Vin × R2 / (R1 + R2). Voltage dividers are used everywhere: setting reference voltages, reading sensors, biasing transistor circuits, and creating ADC input ranges.
A diode allows current to flow in one direction only. It requires a minimum forward voltage (about 0.7V for silicon, 1.8-3.3V for LEDs) to conduct. LEDs (Light Emitting Diodes) are diodes that emit light when forward-biased. Always use a current-limiting resistor with LEDs to prevent burnout.
In Open Circuits, LEDs visually light up when sufficient current flows through them, making it easy to see which parts of your circuit are active.
A bipolar junction transistor (BJT) can act as an electronic switch. An NPN transistor turns ON when a small current flows into its base, allowing a larger current to flow from collector to emitter. A PNP transistor works in reverse — it turns ON when the base is pulled LOW relative to the emitter.
Transistor switches are used to control LEDs, motors, relays, and other loads from low-power logic signals. Open Circuits simulates both NPN and PNP transistors with realistic gain (beta) and saturation behavior.
An op-amp is a high-gain differential amplifier. In Open Circuits, you can build classic op-amp circuits:
Apply what you've learned. Open the editor and start experimenting.