Topic 6 · Control Systems (HL)

Converts physical quantity → electrical voltage. Thermistor, photoresistor, accelerometer, mic.

Analog-to-Digital Converter. SAMPLES voltage at fixed rate; outputs integers (10-bit = 0-1023).

Hz + bits. Higher = more precise but more cost + CPU.

Converts signal → physical action. Motor, servo, valve, heater, LED, speaker.

Digital-to-Analog Converter. Integer → voltage. Often replaced by PWM (fast on/off, average = duty cycle).

Output PULLED BACK toward target. Stabilising. Used in 99% of control systems.

Output AMPLIFIED away from current state. Microphone squeal, fire alarm chain. Rare and dangerous if unbounded.

Intrinsic DELAY between command and physical response. Cannot be removed — only ANTICIPATED.

Output PASSES the target before settling. Caused by lag + naïve control. PID minimises it.

Proportional (current error) + Integral (accumulated error) + Derivative (rate of change). Industry workhorse.

Drives correction proportional to current error magnitude.

Removes steady-state offset (system stuck slightly below target).

Damps approach — slows correction as target is neared → less overshoot.