tempmodule: add smoothing of temp readings.

1 files changed, 39 insertions, 0 deletions

diff --git a/src/tempmodule/main.ino b/src/tempmodule/main.ino
index 58e3dfc..4bb3ad9 100644
--- a/src/tempmodule/main.ino
+++ b/src/tempmodule/main.ino
@@ -26,6 +26,8 @@
 #include "indicator.h"
 #include "temperature.h"
 
+#define arrsize(a) (sizeof(a)/sizeof(*a))
+
 static const unsigned int iled		= 2;	/* D4 */
 static const unsigned int wifiled	= 12;	/* D6 */
 static const unsigned int wifibutton 	= 15;	/* D8 */
@@ -49,6 +51,7 @@ static void wifi_disconnect(void);
 static void blink_led(const int pin, const int ontime, const int offtime);
 static void discover_client(void);
 static void get_data(short int * const data);
+static short int smooth_temp(short int temp);
 void toggle_wifi(void);
 void wifiled_toggle(void);
 
@@ -110,6 +113,8 @@ void loop(void)
 
 	get_data(data);
 
+	data[0] = smooth_temp(data[0]);
+
 	if (wifistate) {
 		udp_push(data, sizeof(data));
 		/* if flushing fails, disconnect WiFi */
@@ -226,6 +231,40 @@ static void get_data(short int * const data)
 	data[0] = get_temperature(data[1]);
 }
 
+static short int smooth_temp(short int temp)
+{
+	static short int rb[16]; /*ring buffer for smoothing over 16 entries */
+	static size_t offset;
+	short int ret;
+	int sum;
+	size_t i;
+	static unsigned int notfresh;
+
+	/* push value to the ring buffer */
+	if (offset < arrsize(rb)) {
+		rb[offset] = temp;
+		++offset;
+	} else {
+		offset = 0;
+		notfresh = 1;
+		rb[offset] = temp;
+	}
+
+	if (notfresh) {
+		for (i = 0, sum = 0; i < arrsize(rb); ++i) {
+			sum += rb[i];
+		}
+		ret = sum / arrsize(rb);
+	} else {
+		for (i = 0, sum = 0; i < offset; ++i) {
+			sum += rb[i];
+		}
+		ret = sum / offset;
+	}
+
+	return ret;
+}
+
 void toggle_wifi(void)
 {
 	static const unsigned int timeout = 2 * 1000 * 1000;	/* 2 seconds */