PeakDetector

This unit detects peaks (minima or maxima) in an incoming signal. Peaks are detected based on crossing a trigger threshold above (or below) which a peak is detected.

Two different ways are supported to do this:

• In crossing modes (PEAK_RISING and PEAK_FALLING) the peak is detected as soon as the signal crosses the triggerThreshold.

• In apex modes (PEAK_MAX and PEAK_MIN) the peak is detected after the signal crosses the triggerThreshold, reaches its apex, and then falls back by a certain proportion (%) between the threshold and the apex (controlled by the fallbackTolerance parameter).

In all cases, after a peak is detected, the detector will wait until the signal crosses back the reloadThreshold (which can be adjusted to control detection sensitivity) before it can be triggered again.

In summary, the four different modes available are:

• PEAK_RISING : peak detected as soon as value >= triggerThreshold, then wait until value < reloadThreshold

• PEAK_FALLING : peak detected as soon as value <= triggerThreshold, then wait until value > reloadThreshold

• PEAK_MAX : peak detected after value >= triggerThreshold and then falls back after peaking; then waits until value < reloadThreshold

• PEAK_MIN : peak detected after value <= triggerThreshold and then falls back after peaking; then waits until value > reloadThreshold

Note

Before sending a signal to a PeakDetector unit, it is recommended to normalize signals, preferably using the Normalizer unit. Furthermore, to avoid a noisy signal to generate false peaks, it is recommended to smooth the signal by calling the source unit’s smooth() method or by using a Smoother unit.

Example

Uses a Normalizer and a PeakDetector to analyze input sensor values and detect peaks. Toggle and LED each time a peak is detected.

#include <Plaquette.h>

// Analog sensor (eg. photocell or microphone).
AnalogIn sensor(A0);

// Normalization unit to normalize values.
Normalizer normalizer;

// Peak detector. Threshold is set at 1.5 standard deviations above normal.
PeakDetector detector(normalizer.highOutlierThreshold(1.5)); // default mode = PEAK_MAX
// NOTE: You can change mode using optional 2nd parameter, example:
// PeakDetector detector(1.5, PEAK_FALLING));

// Digital LED output.
DigitalOut led;

void begin() {
  // Adjust reload threshold to smaller value than reloadThreshold.
  detector.reloadThreshold(normalizer.highOutlierThreshold(1.0));

  // Adjust fallback tolerance as % between apex and trigger threshold.
  detector.fallbackTolerance(0.2); // 0.2 = 20% (default: 10%)

  // Smooth signal to avoid false peaks due to noise.
  sensor.smooth();

  // Set a time window of 1 minute (60 seconds) on normalizer.
  // This will allow the normalier to slowly readjust itself
  // if the lighting conditions change.
  normalizer.timeWindow(60.0f);
};

void step() {
  // Signal is normalized and sent to peak detector.
  sensor >> normalizer >> detector;

  // Toggle LED when peak detector triggers.
  if (detector)
    led.toggle();
}

Reference

class PeakDetector : public DigitalNode

Emits a signals when a signal peaks.

Public Functions

PeakDetector(float triggerThreshold, uint8_t mode = PEAK_MAX)

Constructor.

Possible modes are:

• PEAK_RISING : peak detected when value becomes >= triggerThreshold, then wait until it becomes < reloadThreshold (*)

• PEAK_FALLING : peak detected when value becomes <= triggerThreshold, then wait until it becomes > reloadThreshold (*)

• PEAK_MAX : peak detected after value becomes >= triggerThreshold and then falls back after peaking; then waits until it becomes < reloadThreshold (*)

• PEAK_MIN : peak detected after value becomes <= triggerThreshold and then rises back after peaking; then waits until it becomes > reloadThreshold (*)

Parameters:

• triggerThreshold – value that triggers peak detection

• mode – peak detection mode

void triggerThreshold(float triggerThreshold)

Sets triggerThreshold.

inline float triggerThreshold() const

Returns triggerThreshold.

void reloadThreshold(float reloadThreshold)

Sets minimal threshold that “resets” peak detection in crossing (rising/falling) and peak (min/max) modes.

inline float reloadThreshold() const

Returns minimal value “drop” for reset.

void fallbackTolerance(float fallbackTolerance)

Sets minimal relative “drop” after peak to trigger detection in peak (min/max) modes, expressed as proportion (%) of peak minus triggerThreshold.

inline float fallbackTolerance() const

Returns minimal relative “drop” after peak to trigger detection in peak modes.

bool modeInverted() const

Returns true if mode is PEAK_FALLING or PEAK_MIN.

bool modeCrossing() const

Returns true if mode is PEAK_RISING or PEAK_FALLING.

void mode(uint8_t mode)

Sets mode.

inline uint8_t mode() const

Returns mode.

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 bool isOn()

Returns true iff the triggerThreshold is crossed.

inline virtual float get()

Returns value as float (either 0.0 or 1.0).

See Also

• Normalizer

• MinMaxScaler

• Smoother