temp.c: allow smoothing temperature readings.

This is done by an Exponentially Weighted Moving Average (EWMA)
formula. Contribution by DaveX, see
http://forums.reprap.org/read.php?147,33082,157978#msg-157978

Thanks a lot, Dave.

config.default.h

@@ -251,6 +251,19 @@
 */
 #define	TEMP_RESIDENCY_TIME		60
 
+/**
+  TEMP_EWMA: Smooth noisy temperature sensors. Good hardware shouldn't be
+  noisy. Set to 1.0 for unfiltered data (and a 140 bytes smaller binary).
+
+  Instrument Engineer's Handbook, 4th ed, Vol 2 p126 says values of
+  0.05 to 0.1 are typical. Smaller is smoother but slower adjusting, larger is
+  quicker but rougher. If you need to use this, set the PID parameter to zero
+  (M132 S0) to make the PID loop insensitive to noise.
+
+  Valid range: 0.001 to 1.0
+*/
+#define TEMP_EWMA             1.0
+
 /// which temperature sensors are you using? List every type of sensor you use here once, to enable the appropriate code. Intercom is the gen3-style separate extruder board.
 // #define	TEMP_MAX6675
 #define	TEMP_THERMISTOR

config.gen3.h

@@ -256,6 +256,19 @@
 */
 #define	TEMP_RESIDENCY_TIME		60
 
+/**
+  TEMP_EWMA: Smooth noisy temperature sensors. Good hardware shouldn't be
+  noisy. Set to 1.0 for unfiltered data (and a 140 bytes smaller binary).
+
+  Instrument Engineer's Handbook, 4th ed, Vol 2 p126 says values of
+  0.05 to 0.1 are typical. Smaller is smoother but slower adjusting, larger is
+  quicker but rougher. If you need to use this, set the PID parameter to zero
+  (M132 S0) to make the PID loop insensitive to noise.
+
+  Valid range: 0.001 to 1.0
+*/
+#define TEMP_EWMA             0.1
+
 /// which temperature sensors are you using? List every type of sensor you use here once, to enable the appropriate code. Intercom is the gen3-style separate extruder board.
 // #define	TEMP_MAX6675
 // #define	TEMP_THERMISTOR

config.gen6.h

@@ -251,6 +251,19 @@
 */
 #define	TEMP_RESIDENCY_TIME		60
 
+/**
+  TEMP_EWMA: Smooth noisy temperature sensors. Good hardware shouldn't be
+  noisy. Set to 1.0 for unfiltered data (and a 140 bytes smaller binary).
+
+  Instrument Engineer's Handbook, 4th ed, Vol 2 p126 says values of
+  0.05 to 0.1 are typical. Smaller is smoother but slower adjusting, larger is
+  quicker but rougher. If you need to use this, set the PID parameter to zero
+  (M132 S0) to make the PID loop insensitive to noise.
+
+  Valid range: 0.001 to 1.0
+*/
+#define TEMP_EWMA             0.1
+
 /// which temperature sensors are you using? List every type of sensor you use here once, to enable the appropriate code. Intercom is the gen3-style separate extruder board.
 // #define	TEMP_MAX6675
 #define	TEMP_THERMISTOR

config.gen7-v1.1-v1.3.h

@@ -259,6 +259,19 @@
 */
 #define	TEMP_RESIDENCY_TIME		60
 
+/**
+  TEMP_EWMA: Smooth noisy temperature sensors. Good hardware shouldn't be
+  noisy. Set to 1.0 for unfiltered data (and a 140 bytes smaller binary).
+
+  Instrument Engineer's Handbook, 4th ed, Vol 2 p126 says values of
+  0.05 to 0.1 are typical. Smaller is smoother but slower adjusting, larger is
+  quicker but rougher. If you need to use this, set the PID parameter to zero
+  (M132 S0) to make the PID loop insensitive to noise.
+
+  Valid range: 0.001 to 1.0
+*/
+#define TEMP_EWMA             1.0
+
 /// which temperature sensors are you using? List every type of sensor you use here once, to enable the appropriate code. Intercom is the gen3-style separate extruder board.
 // #define	TEMP_MAX6675
 #define	TEMP_THERMISTOR

config.gen7-v1.4.h

@@ -259,6 +259,19 @@
 */
 #define	TEMP_RESIDENCY_TIME		60
 
+/**
+  TEMP_EWMA: Smooth noisy temperature sensors. Good hardware shouldn't be
+  noisy. Set to 1.0 for unfiltered data (and a 140 bytes smaller binary).
+
+  Instrument Engineer's Handbook, 4th ed, Vol 2 p126 says values of
+  0.05 to 0.1 are typical. Smaller is smoother but slower adjusting, larger is
+  quicker but rougher. If you need to use this, set the PID parameter to zero
+  (M132 S0) to make the PID loop insensitive to noise.
+
+  Valid range: 0.001 to 1.0
+*/
+#define TEMP_EWMA             1.0
+
 /// which temperature sensors are you using? List every type of sensor you use here once, to enable the appropriate code. Intercom is the gen3-style separate extruder board.
 // #define	TEMP_MAX6675
 #define	TEMP_THERMISTOR

config.ramps-v1.2.h

@@ -254,6 +254,19 @@
 */
 #define	TEMP_RESIDENCY_TIME		60
 
+/**
+  TEMP_EWMA: Smooth noisy temperature sensors. Good hardware shouldn't be
+  noisy. Set to 1.0 for unfiltered data (and a 140 bytes smaller binary).
+
+  Instrument Engineer's Handbook, 4th ed, Vol 2 p126 says values of
+  0.05 to 0.1 are typical. Smaller is smoother but slower adjusting, larger is
+  quicker but rougher. If you need to use this, set the PID parameter to zero
+  (M132 S0) to make the PID loop insensitive to noise.
+
+  Valid range: 0.001 to 1.0
+*/
+#define TEMP_EWMA             0.1
+
 /// which temperature sensors are you using? List every type of sensor you use here once, to enable the appropriate code. Intercom is the gen3-style separate extruder board.
 // #define	TEMP_MAX6675
 #define	TEMP_THERMISTOR

config.ramps-v1.3.h

@@ -258,6 +258,19 @@
 */
 #define	TEMP_RESIDENCY_TIME		60
 
+/**
+  TEMP_EWMA: Smooth noisy temperature sensors. Good hardware shouldn't be
+  noisy. Set to 1.0 for unfiltered data (and a 140 bytes smaller binary).
+
+  Instrument Engineer's Handbook, 4th ed, Vol 2 p126 says values of
+  0.05 to 0.1 are typical. Smaller is smoother but slower adjusting, larger is
+  quicker but rougher. If you need to use this, set the PID parameter to zero
+  (M132 S0) to make the PID loop insensitive to noise.
+
+  Valid range: 0.001 to 1.0
+*/
+#define TEMP_EWMA             0.1
+
 /// which temperature sensors are you using? List every type of sensor you use here once, to enable the appropriate code. Intercom is the gen3-style separate extruder board.
 // #define	TEMP_MAX6675
 #define	TEMP_THERMISTOR

config.sanguinololu-v1.1.h

@@ -255,6 +255,19 @@
 */
 #define	TEMP_RESIDENCY_TIME		60
 
+/**
+  TEMP_EWMA: Smooth noisy temperature sensors. Good hardware shouldn't be
+  noisy. Set to 1.0 for unfiltered data (and a 140 bytes smaller binary).
+
+  Instrument Engineer's Handbook, 4th ed, Vol 2 p126 says values of
+  0.05 to 0.1 are typical. Smaller is smoother but slower adjusting, larger is
+  quicker but rougher. If you need to use this, set the PID parameter to zero
+  (M132 S0) to make the PID loop insensitive to noise.
+
+  Valid range: 0.001 to 1.0
+*/
+#define TEMP_EWMA             0.1
+
 /// which temperature sensors are you using? List every type of sensor you use here once, to enable the appropriate code. Intercom is the gen3-style separate extruder board.
 // #define	TEMP_MAX6675
 #define	TEMP_THERMISTOR

config.sanguinololu-v1.2.h

@@ -255,6 +255,19 @@
 */
 #define	TEMP_RESIDENCY_TIME		60
 
+/**
+  TEMP_EWMA: Smooth noisy temperature sensors. Good hardware shouldn't be
+  noisy. Set to 1.0 for unfiltered data (and a 140 bytes smaller binary).
+
+  Instrument Engineer's Handbook, 4th ed, Vol 2 p126 says values of
+  0.05 to 0.1 are typical. Smaller is smoother but slower adjusting, larger is
+  quicker but rougher. If you need to use this, set the PID parameter to zero
+  (M132 S0) to make the PID loop insensitive to noise.
+
+  Valid range: 0.001 to 1.0
+*/
+#define TEMP_EWMA             0.1
+
 /// which temperature sensors are you using? List every type of sensor you use here once, to enable the appropriate code. Intercom is the gen3-style separate extruder board.
 // #define	TEMP_MAX6675
 #define	TEMP_THERMISTOR

config.teensy.h

@@ -339,6 +339,19 @@ New plan:
 */
 #define	TEMP_RESIDENCY_TIME		60
 
+/**
+  TEMP_EWMA: Smooth noisy temperature sensors. Good hardware shouldn't be
+  noisy. Set to 1.0 for unfiltered data (and a 140 bytes smaller binary).
+
+  Instrument Engineer's Handbook, 4th ed, Vol 2 p126 says values of
+  0.05 to 0.1 are typical. Smaller is smoother but slower adjusting, larger is
+  quicker but rougher. If you need to use this, set the PID parameter to zero
+  (M132 S0) to make the PID loop insensitive to noise.
+
+  Valid range: 0.001 to 1.0
+*/
+#define TEMP_EWMA             0.1
+
 /// which temperature sensors are you using? List every type of sensor you use here once, to enable the appropriate code. Intercom is the gen3-style separate extruder board.
 // #define	TEMP_MAX6675
 #define	TEMP_THERMISTOR

temp.c

@@ -289,7 +289,17 @@ void temp_sensor_tick() {
 				default: /* prevent compiler warning */
 					break;
 			}
-			temp_sensors_runtime[i].last_read_temp = temp;
+			/* Exponentially Weighted Moving Average alpha constant for smoothing
+			   noisy sensors. Instrument Engineer's Handbook, 4th ed, Vol 2 p126
+			   says values of 0.05 to 0.1 for TEMP_EWMA are typical. */
+			#ifndef TEMP_EWMA
+				#define TEMP_EWMA 1.0
+			#endif
+			#define EWMA_SCALE  1024L
+			#define EWMA_ALPHA  ((long) (TEMP_EWMA * EWMA_SCALE))
+			temp_sensors_runtime[i].last_read_temp = (EWMA_ALPHA * temp +
+			  (EWMA_SCALE-EWMA_ALPHA) * temp_sensors_runtime[i].last_read_temp
+			                                         ) / EWMA_SCALE;
 		}
 		if (labs((int16_t)(temp_sensors_runtime[i].last_read_temp - temp_sensors_runtime[i].target_temp)) < (TEMP_HYSTERESIS*4)) {
 			if (temp_sensors_runtime[i].temp_residency < (TEMP_RESIDENCY_TIME*120))