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# Battery Driver
This driver provides support for directly sampling battery level.
## Usage
To use this driver, add the following to your `rules.mk`:
```make
BATTERY_DRIVER_REQUIRED = yes
```
::::info Note
This is already configured for you if you are using the [Battery](../features/battery) feature.
::::
## Driver Configuration {#driver-configuration}
Driver selection can be configured in `rules.mk` as `BATTERY_DRIVER`. Valid values are `adc`, `vendor`, or `custom`. See below for information on individual drivers.
### ADC Driver {#adc-driver}
The default configuration assumes the battery is connected to a ADC capable pin through a voltage divider.
```make
BATTERY_DRIVER = adc
```
The following `#define`s apply only to the `adc` driver:
|Define |Default |Description |
|---------------------------------|--------------|--------------------------------------------------------------|
|`BATTERY_ADC_PIN` |*Not defined* |The GPIO pin connected to the voltage divider. |
|`BATTERY_ADC_REF_VOLTAGE_MV` |`3300` |The ADC reverence voltage, in millivolts. |
|`BATTERY_ADC_VOLTAGE_DIVIDER_R1` |`100` |The voltage divider resistance, in kOhm. Set to 0 to disable. |
|`BATTERY_ADC_VOLTAGE_DIVIDER_R2` |`100` |The voltage divider resistance, in kOhm. Set to 0 to disable. |
|`BATTERY_ADC_RESOLUTION` |`10` |The ADC resolution configured for the ADC Driver. |
### Custom Driver {#custom-driver}
A custom driver is expected to implement the following interface:
```c
void battery_driver_init(void) {
// Perform any initialisation here
}
uint8_t battery_driver_sample_percent(void) {
// Read and return current state here
return value;
}
```
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