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Add virtual current sensor documentation 

..and remove a couple of defines I didn't use.
This commit is contained in:
tracernz 2015-01-16 22:47:10 +13:00
parent a37c6ee9ee
commit a81fad9cc2
2 changed files with 31 additions and 3 deletions
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32
docs/Battery.md
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@ -74,8 +74,19 @@ Enable current monitoring using the CLI command
feature CURRENT_METER
```
Configure the current meter type using the `current_meter_type` settings as per the following table.
| Value | Sensor Type |
| ----- | ---------------------- |
| 0 | None |
| 1 | ADC/hardware sensor |
| 2 | Virtual sensor |
Configure capacity using the `battery_capacity` setting, which takes a value in mAh.
If you're using an OSD that expects the multiwii current meter output value, then set `multiwii_current_meter_output` to `1` (this multiplies amperage sent to MSP by 10).
### ADC Sensor
The current meter may need to be configured so that the value read at the ADC input matches actual current draw. Just like you need a voltmeter to correctly calibrate your voltage reading you also need an ammeter to calibrate your current sensor.
Use the following settings to adjust calibration.
@ -83,4 +94,23 @@ Use the following settings to adjust calibration.
`current_meter_scale`
`current_meter_offset`
If you're using an OSD that expects the multiwii current meter output value, then set `multiwii_current_meter_output` to `1`.
### Virtual Sensor
The virtual sensor uses the throttle position to calculate as estimated current value. This is useful when a real sensor is not available. The following settings adjust the calibration.
| Setting | Description |
| ----------------------------- | -------------------------------------------------------- |
| `current_meter_scale` | The throttle scaling factor [centiamps, i.e. 1/100th A] |
| `current_meter_offset` | The current at zero throttle [centiamps, i.e. 1/100th A] |
If you know your current at zero throttle (Imin) and maximum throttle(Imax) you can calculate the scaling factors using the following formulas where Tmax is maximum throttle offset (i.e. for `max_throttle` = 1850, Tmax = 1850 - 1000 = 850):
```
current_meter_scale = (Imax - Imin) * 100000 / (Tmax + (Tmax * Tmax / 50))
current_meter_offset = Imin * 100
```
e.g. For a maximum current of 34.2 A and minimum current of 2.8 A with `max_throttle` = 1850
```
current_meter_scale = (Imax - Imin) * 100000 / (Tmax + (Tmax * Tmax / 50))
= (34.2 - 2.8) * 100000 / (850 + (850 * 850 / 50))
= 205
current_meter_offset = Imin * 100 = 280
```

2
src/main/sensors/battery.h
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@ -20,8 +20,6 @@
#define VBAT_SCALE_DEFAULT 110
#define VBAT_SCALE_MIN 0
#define VBAT_SCALE_MAX 255
#define VIRTUAL_CURRENT_MIN 0
#define VIRTUAL_CURRENT_MAX 0xffff
typedef enum {
CURRENT_SENSOR_NONE = 0,