A schematic is a map of a circuit's electrical connections, not its physical layout. It deliberately ignores where parts sit on a board and shows only what connects to what. Learning to read one fluently is the difference between guessing at a circuit and understanding it.
Common symbols
Each component has a standard symbol and a reference designator (a letter plus a number, like R1 or C3):
- Resistor — a zig-zag or rectangle, designator R.
- Capacitor — two parallel lines (one curved for polarised electrolytics), designator C.
- Diode / LED — a triangle pointing into a bar; the LED adds arrows for emitted light, designator D.
- Battery / DC source — long and short parallel lines, or a circle, designator V or BT.
- Ground — a downward set of shrinking horizontal bars, the common 0 V reference.
Wires, junctions and nodes
Lines are wires — ideal, zero-resistance connections. Where wires join electrically, a solid dot marks the junction. Wires that cross without a dot are not connected; they simply pass over one another on the page.
A node is any set of points connected together by wire. Every point on a node is at the same voltage. Recognising nodes is the key skill: redraw a tangled schematic by its nodes and the series and parallel groupings usually become obvious.
One node = one voltage
The ground reference
Voltage is always a difference between two points, so we need a reference to measure against. The ground symbol marks that reference — defined as 0 V. Every other node voltage in the circuit is stated relative to ground.
This is why a simulator insists on a ground: without a fixed reference, the node voltages have no defined values (only their differences would be known). Pick one node as ground and the solver can assign an absolute voltage to every other node.