> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/vedderb/bldc/llms.txt
> Use this file to discover all available pages before exploring further.

# PAS application

> Configure pedal assist for e-bikes using a cadence or torque sensor.

The PAS (Pedal Assist System) application is designed for e-bikes. It reads a crank rotation sensor and scales motor current proportionally to pedaling cadence or torque, providing assistance that feels natural under pedaling effort.

## Sensor types

The firmware currently supports one sensor type:

```c theme={null}
typedef enum {
    PAS_SENSOR_TYPE_QUADRATURE = 0
} pas_sensor_type;
```

A quadrature PAS sensor outputs two phase-shifted pulse trains, allowing the firmware to detect both cadence (speed of pedaling) and pedaling direction.

## Control types

```c theme={null}
typedef enum {
    PAS_CTRL_TYPE_NONE = 0,
    PAS_CTRL_TYPE_CADENCE,
    PAS_CTRL_TYPE_TORQUE,
    PAS_CTRL_TYPE_TORQUE_WITH_CADENCE_TIMEOUT
} pas_control_type;
```

| Type                          | Description                                                                                             |
| ----------------------------- | ------------------------------------------------------------------------------------------------------- |
| `CADENCE`                     | Motor current scales with pedal RPM between `pedal_rpm_start` and `pedal_rpm_end`.                      |
| `TORQUE`                      | Motor current scales with measured crank torque.                                                        |
| `TORQUE_WITH_CADENCE_TIMEOUT` | Torque mode, but output cuts if cadence drops to zero for more than `MAX_MS_WITHOUT_CADENCE` (1000 ms). |

## Configuration struct

```c theme={null}
typedef struct {
    pas_control_type ctrl_type;
    pas_sensor_type sensor_type;
    float current_scaling;
    float pedal_rpm_start;
    float pedal_rpm_end;
    bool invert_pedal_direction;
    uint8_t magnets;
    bool use_filter;
    float ramp_time_pos;
    float ramp_time_neg;
    uint32_t update_rate_hz;
} pas_config;
```

### Key parameters

| Field                    | Default | Description                                                                    |
| ------------------------ | ------- | ------------------------------------------------------------------------------ |
| `pedal_rpm_start`        | 10 RPM  | Cadence at which assist begins.                                                |
| `pedal_rpm_end`          | 180 RPM | Cadence at which assist reaches maximum.                                       |
| `current_scaling`        | 0.1     | Fraction of maximum motor current applied at full assist.                      |
| `magnets`                | 24      | Number of magnet pulses per crank revolution on the sensor.                    |
| `invert_pedal_direction` | `false` | Swap forward/reverse pedaling direction detection.                             |
| `use_filter`             | `true`  | Smooths cadence measurement with a moving-average filter.                      |
| `safe_start`             | `true`  | Requires pedaling to stop and restart before assist is allowed after power-on. |
| `ramp_time_pos`          | 0.6 s   | Ramp time for increasing assist.                                               |
| `ramp_time_neg`          | 0.3 s   | Ramp time for decreasing assist.                                               |
| `update_rate_hz`         | 500 Hz  | Control loop rate.                                                             |

## Timing constants

Defined in `app_pas.c`:

```c theme={null}
#define PEDAL_INPUT_TIMEOUT                  0.2    // seconds
#define MAX_MS_WITHOUT_CADENCE_OR_TORQUE     5000   // ms
#define MAX_MS_WITHOUT_CADENCE               1000   // ms
#define MIN_MS_WITHOUT_POWER                 500    // ms
```

If no sensor pulses arrive within `PEDAL_INPUT_TIMEOUT` (0.2 s), the pedal RPM reading is treated as zero. If cadence is absent for longer than `MAX_MS_WITHOUT_CADENCE_OR_TORQUE` (5 s), motor output stops entirely.

## Wiring

Connect the PAS sensor to the expansion connector pins designated for quadrature input on your VESC hardware variant. The sensor requires:

* Signal A and Signal B pulse outputs (open-drain or push-pull, 3.3 V compatible)
* 5 V or 3.3 V supply
* Common ground

<Warning>
  Do not connect a 5 V sensor output directly if your VESC hardware input pins are 3.3 V only. Use a resistor divider or level shifter.
</Warning>

## Combining with ADC throttle

Select `APP_ADC_PAS` to run both the ADC throttle application and PAS simultaneously. In this mode the ADC throttle acts as an override: if the rider applies the throttle lever, ADC output takes precedence over pedal assist.

## Runtime API

```c theme={null}
void  app_pas_start(bool is_primary_output);
void  app_pas_stop(void);
bool  app_pas_is_running(void);
void  app_pas_configure(pas_config *conf);
float app_pas_get_current_target_rel(void); // Relative current target (0–1)
float app_pas_get_pedal_rpm(void);
void  app_pas_set_current_sub_scaling(float current_sub_scaling);
```

`app_pas_set_current_sub_scaling` lets another module (such as a throttle override) reduce the PAS output current without modifying the stored configuration.