A comment is added for TFmini valid minimum parameter.

src/drivers/distance_sensor/tfmini/TFMINI.cpp

@@ -60,6 +60,11 @@ TFMINI::init()
 
 	switch (hw_model) {
 	case 1: // TFMINI (12m, 100 Hz)
+		// Note:
+		// Sensor specification shows 0.3m as minimum, but in practice
+		// 0.3 is too close to minimum so chattering of invalid sensor decision
+		// is happening sometimes. this cause EKF to believe inconsistent range readings.
+		// So we set 0.4 as valid minimum.
 		_px4_rangefinder.set_min_distance(0.4f);
 		_px4_rangefinder.set_max_distance(12.0f);
 		_px4_rangefinder.set_fov(math::radians(1.15f));