Concepts
The theory behind every circuit — the rules the simulator obeys.
The circuit loop
Current only flows around a CLOSED loop: out of the battery’s + terminal, through every part, back into −. Break the loop anywhere and everything stops. That’s all a circuit is — a round trip for charge.
Ohm’s law
Voltage pushes, resistance resists, current is what results. Double the resistance and half the current flows; double the voltage and it doubles. Every readout in this game obeys this one line.
Electrical power
Power is how fast energy is delivered — what makes lamps bright and parts hot. It’s voltage times current, so a lamp glows brightest when it gets both volts across it and amps through it.
Series vs parallel
In series, parts share one path — the same current flows through each, and resistances ADD. In parallel, parts offer separate paths — each gets the full voltage, and total resistance DROPS. Most circuit design is choosing between these two.
Current limiting
Some parts (LEDs especially) don’t limit their own current — connect them straight to a battery and they fry. A series resistor sets the current: the resistor takes the leftover voltage, and Ohm’s law tells you what flows.
Diodes: one-way streets
A diode conducts in only one direction, and only after its forward voltage (~0.7V, LEDs ~2V) is overcome. Backwards, it blocks entirely. That asymmetry is the seed of ALL electronics.
The voltage divider
Two resistors in series split the supply voltage in proportion to their resistances. The midpoint voltage is the workhorse of sensing: swap one resistor for a sensor and the midpoint moves with light or temperature.
Fuses: sacrificial protection
A fuse is a thin wire that melts when too much current flows, breaking the circuit before anything expensive burns. It protects by dying — always size it above normal current but below what your parts can survive.
Using meters
An ammeter measures current THROUGH itself, so it goes IN the loop (series) and has near-zero resistance. A voltmeter measures voltage ACROSS two points, so it connects in parallel and has huge resistance. Swap them and you get a short or a broken loop.
The Wheatstone bridge
Two voltage dividers side by side; a meter spans their midpoints. When the ratios match, the bridge is balanced and the meter reads zero — tiny imbalances become measurable. This is how precision sensing works.
Capacitors & RC time
A capacitor stores charge; current flows only while its voltage is catching up to the supply. With a resistor in the path, the catch-up takes time — the RC time constant. That’s how circuits remember, delay, and smooth.
Relays: current controls current
A relay is a switch thrown by an electromagnet: enough current through the coil pulls the contact over. A small, safe current can switch a big one — the mechanical ancestor of the transistor.
Systematic fault-finding
A dead circuit fails for exactly one reason at a time: an open (break) or a short (unwanted path). Probe voltages: a full supply voltage across ONE part means it’s open; zero volts across a part that should drop some means it’s shorted or bypassed.
Transistors: the electronic switch
A tiny base/gate current or voltage controls a much larger collector current — a relay with no moving parts, millions of times faster. Amplifiers, logic, computers: all built from this.
Ratings & burnout
Every real component has a limit — a lamp’s wattage, an LED’s max current, a resistor’s power rating. Push past it for long and the part overheats and burns out (goes open, dead). The fix is always the same: limit the current or spread the load so each part stays safely under its rating.
Inductors & electromagnets
Current through a coil builds a magnetic field, and the coil fights any CHANGE in that current. Steady current passes freely; sudden changes are resisted. The stored field is also what pulls relay contacts.
Components
Everything on the shelf, with the physics each part obeys.
Power
The classic power source: a fixed voltage between + and −. It pushes current around the loop and every circuit needs a push.
An adjustable bench source — like a battery whose voltage you can dial.
A source that wiggles: sine or square waves at a chosen frequency and amplitude. The tool for exploring how circuits respond to CHANGE.
The battery’s dual: instead of fixing the voltage, it forces a fixed CURRENT through whatever it feeds.
The reference point — 0V by definition. Voltages are always measured relative to somewhere; ground is the agreed somewhere.
Passives
The workhorse. It resists current flow, drops voltage, limits, divides, and turns electrical energy into heat.
A resistor with a movable tap (wiper). Twist it to change the split — volume knobs and dimmers are potentiometers.
Storage
Stores charge like a tiny rechargeable tank. Passes changing current, blocks steady DC — the memory and timing element of circuits.
A coil that stores energy in its magnetic field and fights any change in current. Electromagnets, filters, and relay coils are inductors.
Semiconductors
A one-way valve for current: conducts forward after ~0.7V, blocks completely in reverse.
A diode designed to break down at a precise reverse voltage — and survive it. The classic cheap voltage reference.
The electronic switch and amplifier: a small base current lets a much larger collector current flow.
The NPN’s mirror twin: it turns ON when its base is pulled LOW. Useful for switching the + side of a load.
A voltage-controlled switch: no gate current at all, just a threshold voltage that opens the channel.
Switches & Relays
The simplest control: open (no path) or closed (a plain wire). Everything digital descends from this idea.
Single pole, double throw: one input that connects to either of two outputs — an electrical fork in the road.
A momentary switch — closed only while held. Doorbells, keyboards, and reset buttons.
A switch thrown by an electromagnet: enough coil current pulls the contact over. Small currents switching big ones — the mechanical ancestor of the transistor.
Output
A filament that glows when current heats it. Brightness follows power — the game’s favorite way to SHOW you the circuit state.
A diode that turns current into light. Greedy above its forward voltage — always give it a series resistor.
Turns current into sound. Polarity matters; volume follows power.
Turns current into rotation. Reverse the current and it spins the other way — the heart of every polarity puzzle.
Sensors
A light-dependent resistor: bright light → low resistance, darkness → high. Put it in a divider and light becomes a voltage.
A temperature-dependent resistor. The sensing element in thermostats — heat changes resistance, resistance changes voltage.
Meters
Measures current THROUGH itself — wire it into the loop (series). Nearly zero resistance so it doesn’t disturb what it measures.
Measures voltage ACROSS two points — connect it in parallel. Huge resistance so almost no current detours through it.
Protection
Sacrificial protection: a thin wire that melts above its rated current, breaking the circuit before anything expensive burns.
The best way to learn any of this: build it in the sandbox and watch the numbers.