Thermostats: Bang-Bang Control

You set the AC to 72°F. The house warms up to 73°. The AC kicks on full blast. The house cools to 71°. The AC turns off. The temperature moves in a sine wave: 71… 73… 71… 73. This is Bang-Bang Control (On-Off Control).

Simple but Jerky

Bang-Bang is the simplest code in the world: if (Current > Target) { TurnOn(); } else { TurnOff(); }

• Pros: Easy to code.
• Cons: Overshoot. The system is always oscillating. It’s rough on the machinery (turning a compressor on/off rapidly wears it out).

Hysteresis (The Buffer)

To prevent the AC from flickering on/off every second, we add Hysteresis.

• “Turn ON at 74.”
• “Turn OFF at 70.” This 4-degree gap prevents “Short Cycling.”

Robotics: The Claw

We use Bang-Bang for pneumatics or simple motors.

• “If button pressed, Close Claw.”
• “If button released, Open Claw.” We don’t need a PID loop to close a claw. It’s either Grip or No Grip. But for an Arm? Bang-Bang would cause it to smash up and down violently. For that, we need PID. Knowing when to be simple is part of being a good engineer.