A circuit diagram looks like hieroglyphs. But ten symbols cover most of it, and then you can read it.
First the lines: every line is a wire. A dot where wires cross means they’re connected; no dot, and they just pass over each other.
The ten symbols: the resistor (a zigzag in the US, a box in the international IEC standard), the capacitor, the inductor, the diode, the LED, the switch, the transistor, ground, the power rail, and the chip, a box whose pins each get a number and a name. One more rule: wires with the same name are connected even with no line between them. That’s a net label.
Then we read one real circuit: a microcontroller with a 0.1 µF capacitor next to its power pin, an LED with a 330-ohm resistor on pin 5 (3.3 V minus 1.8 V across a red LED leaves 1.5 V, about 4.5 mA), and a button on pin 2 with a 10 kΩ pull-up: not pressed it reads 1, pressed it reads 0.
Sources:
– SparkFun, How to Read a Schematic: symbols, junction dots, net labels, chip pins with a number and a name.
– Wikipedia, Electronic symbol: IEC 60617 (international) vs IEEE/ANSI 315 (American) resistor symbols.
– SparkFun, Resistors: a red LED drops about 1.8 V; pull-ups around 10 kΩ.
– SparkFun, Capacitors: 0.1 µF decoupling capacitors close to the chip.
– SparkFun, Pull-up Resistors: high when not pressed, low when pressed; built-in pull-ups.
– SparkFun, Diodes and Transistors; Wikipedia, Inductor.
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