Question about EWMA filter libray

Projects Programming
1

In the EWMA filter ( GitHub - jonnieZG/EWMA: Exponentially Weighted Moving Average Filter)
is it possible to change the EWMA parameters inside the loop() ? Bellow is the original code.

#include <Arduino.h>
#include <Ewma.h>

Ewma adcFilter1(0.1);   // Less smoothing - faster to detect changes, but more prone to noise
Ewma adcFilter2(0.01);  // More smoothing - less prone to noise, but slower to detect changes

void setup()
{
    Serial.begin(115200);
    pinMode(A0, INPUT);
}

void loop()
{
    int raw = analogRead(A0);
    float filtered1 = adcFilter1.filter(raw);
    float filtered2 = adcFilter2.filter(raw);
    Serial.printf("Raw=%d, Filter1=%.3f, Filter2=%.3f", raw, filtered1, filtered2);
    
    delay(100);
}
2

Yes.

Set the alpha property:

so:

 adcFilter1.alpha = 0.2;
3

My question is if is possible use the statement like
Ewma adcFilter1(0.1);
INSIDE the loop then change the parameter in the runtime.
By your answer is OK . Right?

4

You probably don't do that -- it would make another Ewma object that would expire at the end of loop.

You can adjust the alpha within the loop. I'm not sure how you'd like to change it but something like this completely untested code should work:

#include <Arduino.h>
#include <Ewma.h>

Ewma adcFilter1(0.1);   // Less smoothing - faster to detect changes, but more prone to noise
Ewma adcFilter2(0.01);  // More smoothing - less prone to noise, but slower to detect changes

void setup()
{
    Serial.begin(115200);
    pinMode(A0, INPUT);
    pinmode(A4, INPUT);
    pinmode(A5, INPUT);
}

void loop()
{
    int raw = analogRead(A0);

    adcFilter1.alpha = analogRead(A4)/1023.0;
    adcFilter2.alpha = analogRead(A5)/1023.0;
    float filtered1 = adcFilter1.filter(raw);
    float filtered2 = adcFilter2.filter(raw);
    Serial.printf("Raw=%d, Filter1=%.3f, Filter2=%.3f", raw, filtered1, filtered2);
    
    delay(100);
}
5

I will put it inside the setup. It should work better. The program may ask the user to adjust the filter weight. After this the program restart from setup. It seems better.

6

Any user-based changes will be lost at the restart.

If you ask and update in setup, any changes during that power cycle will persist throughout that powercycle.

7

why not just implement the filter directly?
K can be changed at run-time, we modified K in speakerphones for depending if samp > avg

const byte PinInp = A1;

float avg;
float K = 1.0 / 8;

// -----------------------------------------------------------------------------
void loop()
{
    float samp = analogRead (PinInp);
    avg += (samp - avg) * K;
    Serial.println (avg);
    delay (200);
}


void setup()
{
    Serial.begin(115200);
    avg = analogRead (PinInp);
}
2 Likes
8

Using libraries to abstract even simple software patterns is a huge help when making complex projects. It's rarely a good idea to implement things like filters directly.

1 Like
9

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