added battery current sensor offset

src/modules/sensors/sensor_params.c

@@ -1960,6 +1960,14 @@ PARAM_DEFINE_FLOAT(BAT_V_SCALING, -1.0f);
  */
 PARAM_DEFINE_FLOAT(BAT_C_SCALING, -1.0);
 
+/**
+ * Offset for battery current sensor.
+ *
+ * @group Battery Calibration
+ * @decimal 8
+ */
+PARAM_DEFINE_FLOAT(BAT_C_OFFSET, -1.0);
+
 
 /**
  * RC channel count

src/modules/sensors/sensors.cpp

@@ -321,6 +321,7 @@ private:
 
 		float battery_voltage_scaling;
 		float battery_current_scaling;
+		float battery_current_offset;
 
 		float baro_qnh;
 
@@ -380,6 +381,7 @@ private:
 
 		param_t battery_voltage_scaling;
 		param_t battery_current_scaling;
+		param_t battery_current_offset;
 
 		param_t board_rotation;
 
@@ -652,6 +654,7 @@ Sensors::Sensors() :
 
 	_parameter_handles.battery_voltage_scaling = param_find("BAT_V_SCALING");
 	_parameter_handles.battery_current_scaling = param_find("BAT_C_SCALING");
+	_parameter_handles.battery_current_offset = param_find("BAT_C_OFFSET");
 
 	/* rotations */
 	_parameter_handles.board_rotation = param_find("SENS_BOARD_ROT");
@@ -927,6 +930,13 @@ Sensors::parameters_update()
 #endif
 	}
 
+	if (param_get(_parameter_handles.battery_current_offset, &(_parameters.battery_current_offset)) != OK) {
+		warnx("%s", paramerr);
+
+	} else if (_parameters.battery_current_offset < 0.0f) {
+		_parameters.battery_current_offset = 0.0f;
+	}
+
 	param_get(_parameter_handles.board_rotation, &(_parameters.board_rotation));
 	get_rot_matrix((enum Rotation)_parameters.board_rotation, &_board_rotation);
 
@@ -1669,7 +1679,7 @@ Sensors::adc_poll(struct sensor_combined_s &raw)
 				} else if (ADC_BATTERY_CURRENT_CHANNEL == buf_adc[i].am_channel) {
 					/* handle current only if voltage is valid */
 					if (_battery_status.voltage_v > 0.0f) {
-						float current = (buf_adc[i].am_data * _parameters.battery_current_scaling);
+						float current = ((buf_adc[i].am_data - _parameters.battery_current_offset) * _parameters.battery_current_scaling);
 
 						/* check measured current value */
 						if (current >= 0.0f) {