From bd1a5902a1a5a764e21b56ba007dfe75463f2472 Mon Sep 17 00:00:00 2001
From: Philip Salmony <34550389+pms67@users.noreply.github.com>
Date: Wed, 27 May 2020 20:49:12 +0200
Subject: [PATCH] Added minus sign to derivative-on-measurement expression.

 Note on 'derivative-on-measurement': Since the 'error signal' effectively going into the differentiator does not depend on the setpoint: e[n] = 0 - measurement,
 and therefore (e[n] - e[n - 1]) = (0 - measurement) - (0 - prevMeasurement) = -Kd * (measurement - prevMeasurement). (Note the minus sign compared to derivative-on-error!)
---
 PID.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/PID.h b/PID.h
index 4ecfe64..bf6b885 100644
--- a/PID.h
+++ b/PID.h
@@ -6,7 +6,7 @@ typedef struct {
 	/* Controller gains */
 	float Kp;
 	float Ki;
-	float Kd; /* Note: since using derivative-on-measurement, Kd needs to be negative (in contrast to conventional 'derivative-on'error') */
+	float Kd;
 
 	/* Derivative low-pass filter time constant */
 	float tau;