Smoother

Smooths the incoming signal by removing fast variations and noise (high frequencies).

_images/Plaquette-Smooth.png

Example

Smooth a sensor over time.

#include <Plaquette.h>

AnalogIn sensor(A0);

// Smooths over time window of 10 seconds.
Smoother smoother(10.0);

StreamOut serialOut(Serial);

void begin() {}

void step() {
  // Smooth value and send it to serial output.
  sensor >> smoother >> serialOut;
}

Note

The filter uses an exponential moving average which corresponds to a form of low-pass filter.

Reference

class Smoother : public Unit, public MovingAverage

Simple moving average transform filter.

Public Functions

Smoother(Engine &engine = Engine::primary())

Constructor with default smoothing.

Parameters: engine – the engine running this unit

Smoother(float smoothingWindow, Engine &engine = Engine::primary())

Constructor with smoothing window.

Parameters

smoothingWindow – the time window over which the smoothing applies (in seconds)
engine – the engine running this unit

virtual float put(float value)

Pushes value into the unit.

Parameters: value – the value sent to the unit
Returns: the new value of the unit

inline virtual float get(): Returns smoothed value.

inline float seconds() const: Returns engine time in seconds.

inline uint32_t milliSeconds() const: Returns engine time in milliseconds.

inline uint64_t microSeconds() const: Returns engine time in microseconds.

inline unsigned long nSteps() const: Returns number of engine steps.

inline float sampleRate() const: Returns engine sample rate.

inline float samplePeriod() const: Returns enginesample period.

inline operator float(): Object can be used directly to access its value.

inline virtual float mapTo(float toLow, float toHigh)

Maps value to new range.

This function guarantees that the value is within [toLow, toHigh]. If the unit’s values are unbounded, returns get() constrained to [toLow, toHigh].

inline explicit operator bool(): Operator that allows usage in conditional expressions.

void infiniteTimeWindow(): Sets to “infinite” smoothing window.

void timeWindow(float seconds): Changes the smoothing window (expressed in seconds).

inline float timeWindow() const: Returns the smoothing window (expressed in seconds).

bool timeWindowIsInfinite() const: Returns true if time window is infinite.

void cutoff(float hz): Changes the smoothing window cutoff frequency (expressed in Hz).

float cutoff() const: Returns the smoothing window cutoff frequency (expressed in Hz).

float alpha(float sampleRate) const: Returns the alpha value computed from given sample rate.

void reset(): Resets the moving average.

virtual float update(float v, float sampleRate = 1, bool forceAlpha = false): Updates the moving average with new value v# (also returns the current value).

inline unsigned int nSamples() const: Returns the number of samples processed since reset().

void amendUpdate(float previousValue, float newValue, float sampleRate = 1, bool forceAlpha = false): Performs an amendment of latest update (needs to be called with same sampleRate# and forceAlpha# parameters).

Public Static Functions

static inline bool analogToDigital(float f): Converts analog (float) value to digital (bool) value.

static inline float digitalToAnalog(bool b): Converts digital (bool) value to analog (float) value.

static float alpha(float sampleRate, float timeWindow, unsigned int nSamples = UINT_MAX): Returns the alpha value computed from given sample rate, time window, and number of samples.

static void applyUpdate(float &runningValue, float newValue, float alpha): Applies a single update on runningValue# with new sample newValue# and mixing factor alpha#.

static void applyAmendUpdate(float &runningValue, float previousValue, float newValue, float alpha): Performs an amendment of latest update (needs to be called with same alpha# parameter).

static float computeUpdate(float runningValue, float newValue, float alpha): Computes a single update on runningValue# with new sample newValue# and mixing factor alpha#.

See Also