Controller Concept

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PID Controller

A robust Arduino-compatible PID controller implementation with improved behavior for slow or overshoot-prone processes.

This implementation extends a basic PID controller with:

• Correct time-based integral and derivative calculations
• Derivative-on-measurement
• Derivative low-pass filtering
• Integral activation range
• Integral tolerance band
• Conditional integration / anti-windup
• Configurable controller direction
• Output limiting
• Output slew-rate limiting
• Rollover-safe millis() handling
• Safe use with multiple PID instances

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Controller Concept

The controller can be described as a PI-D controller:

                         +----------------+
error -----------------> | P              | ----+
                         +----------------+     |
                                                |
                         +----------------+     |
error -----------------> | I              | ----+----> Output limit
                         | Anti-Windup    |     |          |
                         +----------------+     |          v
                                                |      Slew-rate
actual ---> derivative ---> LPF ---> D --------+          |
                                                           v
                                                         output

The proportional and derivative terms are always active.

The integral term is conditionally active depending on:

• the configured tolerance around the setpoint
• the configured integral activation range
• output saturation

This prevents excessive integral accumulation and therefore helps reduce overshoot.

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