airspeed: use floating point values and better averaging in zero_airspeed()

this makes the calibration of airspeed a bit more accurate, and
prevents truncation of airspeed values

ArduCopter/test.pde

@@ -422,7 +422,7 @@ test_radio(uint8_t argc, const Menu::arg *argv)
 
 	while(1){
 		for(int i = 0; i < 9; i++){
-			Serial.printf_P(PSTR("%u,"),adc.Ch(i));
+			Serial.printf_P(PSTR("%.1f,"),adc.Ch(i));
 		}
 		Serial.println();
 		delay(20);

ArduPlane/ArduPlane.pde

@@ -364,7 +364,7 @@ static float	current_total;
 // Airspeed Sensors
 // ----------------
 static float   airspeed_raw;                       // Airspeed Sensor - is a float to better handle filtering
-static int     airspeed_pressure;					// airspeed as a pressure value
+static float   airspeed_pressure;					// airspeed as a pressure value
 
 // Barometer Sensor variables
 // --------------------------

ArduPlane/sensors.pde

@@ -80,9 +80,9 @@ static void read_airspeed(void)
             airspeed_raw = (float)adc.Ch(AIRSPEED_CH);
             g.airspeed_offset.set_and_save(airspeed_raw);
 		}
-		airspeed_raw 		= ((float)adc.Ch(AIRSPEED_CH) * .25) + (airspeed_raw * .75);
-		airspeed_pressure 	= max(((int)airspeed_raw - g.airspeed_offset), 0);
-		airspeed 			= sqrt((float)airspeed_pressure * g.airspeed_ratio) * 100;
+		airspeed_raw 		= (adc.Ch(AIRSPEED_CH) * 0.25) + (airspeed_raw * 0.75);
+		airspeed_pressure 	= max((airspeed_raw - g.airspeed_offset), 0);
+		airspeed 			= sqrt(airspeed_pressure * g.airspeed_ratio) * 100;
 	#endif
 
 	calc_airspeed_errors();
@@ -90,12 +90,15 @@ static void read_airspeed(void)
 
 static void zero_airspeed(void)
 {
-	airspeed_raw = (float)adc.Ch(AIRSPEED_CH);
-	for(int c = 0; c < 10; c++){
-		delay(20);
-		airspeed_raw = (airspeed_raw * .90) + ((float)adc.Ch(AIRSPEED_CH) * .10);
+    float sum = 0;
+    int c;
+	airspeed_raw = adc.Ch(AIRSPEED_CH);
+	for(c = 0; c < 250; c++) {
+		delay(2);
+		sum += adc.Ch(AIRSPEED_CH);
 	}
-	g.airspeed_offset.set_and_save(airspeed_raw);
+    sum /= c;
+	g.airspeed_offset.set_and_save((int16_t)sum);
 }
 
 #endif // HIL_MODE != HIL_MODE_ATTITUDE

ArduPlane/test.pde

@@ -459,7 +459,7 @@ test_adc(uint8_t argc, const Menu::arg *argv)
 	delay(1000);
 
 	while(1){
-		for (int i=0;i<9;i++) Serial.printf_P(PSTR("%u\t"),adc.Ch(i));
+		for (int i=0;i<9;i++) Serial.printf_P(PSTR("%.1f\t"),adc.Ch(i));
 		Serial.println();
 		delay(100);
 		if(Serial.available() > 0){
@@ -630,9 +630,9 @@ test_mag(uint8_t argc, const Menu::arg *argv)
 static int8_t
 test_airspeed(uint8_t argc, const Menu::arg *argv)
 {
-    unsigned airspeed_ch = adc.Ch(AIRSPEED_CH);
+    float airspeed_ch = adc.Ch(AIRSPEED_CH);
 	// Serial.println(adc.Ch(AIRSPEED_CH));
-    Serial.printf_P(PSTR("airspeed_ch: %u\n"), airspeed_ch);
+    Serial.printf_P(PSTR("airspeed_ch: %.1f\n"), airspeed_ch);
 
 	if (g.airspeed_enabled == false){
 		Serial.printf_P(PSTR("airspeed: "));
@@ -648,7 +648,7 @@ test_airspeed(uint8_t argc, const Menu::arg *argv)
 		while(1){
 			delay(20);
 			read_airspeed();
-			Serial.printf_P(PSTR("%fm/s\n"), airspeed / 100.0);
+			Serial.printf_P(PSTR("%.1f m/s\n"), airspeed / 100.0);
 
 			if(Serial.available() > 0){
 				return (0);