Redstone torch — the inverter
The redstone torch powers circuits and inverts signals: feed power into the block it sits on and it turns off. That single behavior is an NOT gate, the seed of every logic circuit. Torches also power doors, pistons and lamps directly with a 15-block wire range.
Repeater and comparator
A repeater extends signal another 15 blocks, adds a tickable delay (1–4), and acts as a one-way diode. A comparator reads containers (output strength = fullness), compares two signals, or subtracts — comparators turn chests and cake into sensors.
Observer — the change detector
The observer emits a pulse when the block in front of it changes (crop growth, block placement, machine states). Observers built the modern automatic farm: sugarcane grows → observer fires → piston breaks → item stream to hoppers. Build a sugarcane or pumpkin farm as your first contraption; it is practical and teaches pulses, pistons and hoppers in one build.
