drivers.encoder module

class drivers.encoder.Encoder(tim, chA_pin, chB_pin)

Bases: object

Quadrature encoder interface wrapper.

• Uses a hardware Timer configured in ENC_AB mode with two channels (channel 1 -> A, channel 2 -> B).

• Tracks total accumulated encoder position accounting for timer reloads (overflow / underflow).

• Provides update() to sample the hardware counter and compute:

  • position: total encoder counts (signed, extended across reloads)

  • delta: change in position since last update (counts)

  • dt: elapsed time since last update (milliseconds, float)

• Convenience methods:

  • get_position() -> wheel linear position (mm)

  • get_velocity() -> linear velocity (mm/s)

  • zero() -> reset the encoder zero (tare)

get_position()

Convert the most recently-updated encoder position (counts) into a linear wheel displacement in millimeters.

Formula:

rotations = counts / ECOUNTS_PER_WREV distance = rotations * (2 * pi * wheel_radius)

get_velocity()

Compute linear velocity (mm/s) using the most recent delta and dt.

Returns 0 if dt is zero (to avoid division by zero). The computation follows:

counts_per_ms = delta / dt
rotations_per_s = (counts_per_ms * 1000) / ECOUNTS_PER_WREV
velocity_mm_s = rotations_per_s * (2 * pi * wheel_radius)

update()

Sample the hardware counter and update position/delta/dt.

• Reads the raw 16-bit counter

• Extends it using self.timer_reloads to build a monotonic position

• Computes delta = position - prev_count

• Updates prev_count and computes elapsed time dt (ms)

zero()

Tare / zero the encoder.

• Reset reload counters and prev_count

• Reset the hardware timer counter to 0

• Call update() so subsequent reads are consistent with the new zero