Change number of samples on smooth average

[rafaellehmkuhl]

First of all, congratulations for the library. This was the only one I used that managed to get data from multiple HX711 without any problem.

My question: is there a way to change the number of samples used for the smooth average without changing the library (HX711_ADC.h) itself? As far as I noticed there isn't any function to change this variable.

If there isn't indeed, would you accept it as a Pull Request?

[olkal]

Thanks, I'm glad you like it!

First of all, the value that decides the number of samples is a definition, not a variable, hence it can not be changed after compilation.

The scetch and the library files are compiled seperatly, and I'm not aware of any way to pass a value from the scetch that will affect the compilation of the library. You could make a way to pass a value in the scetch to reduce the numper of samples actually used by the library, but as the size of the declared dataset array directly affects memory usage it's not a good ida to declare a larger dataset array than you actually need.

So the anwer is no, unless someone can come up with a way to do this without making the library more complicated to use, and without using more memory than neccesary.

Olav

[jpk73]

Hi, I also would be interested in a way to change the number of samples: I am changing the speed on the fly and would like to adjust the number of samples together with the speed change. Would that be possible?

[olkal]

Hi
Well, yes that should be possible by compiling the full data set and then (on the fly) restricting the library to operate with only a given limited section of the full set. I'm re-opening this Issue. Give me a couple of days and I will look into it.

[jpk73]

Thanks, that will help a lot!

[olkal]

Hi!
You should now be able to use the new function setSamplesInUse(int samples) and getSamplesInUse() to manipulate/override the number of samples in use at the time to a lower value than defined in the config.h file. Note that the memory usage will reflect that of the compiled data set and will not be reduced by using this function.

[jpk73]

Hi! That helps, thanks a lot! And I can confirm that everything works well on the ADS1231. Just had to do new calibrations because the tare factor changed, but that's no problem at all. I just your old calibration sketch and modified it to give me filtered results, in case you are interested I copy it here:

//-------------------------------------------------------------------------------------
// HX711_ADC.h
// Arduino master library for HX711 24-Bit Analog-to-Digital Converter for Weigh Scales
// Olav Kallhovd sept2017
// Tested with      : HX711 asian module on channel A and YZC-133 3kg load cell
// Tested with MCU  : Arduino Nano
//-------------------------------------------------------------------------------------
/* This is an example sketch on how to find correct calibration factor for your HX711:
   - Power up the scale and open Arduino serial terminal
   - After stabelizing and tare is complete, put a known weight on the load cell
   - Observe values on serial terminal
   - Adjust the calibration factor until output value is same as your known weight:
      - Sending 'l' from the serial terminal decrease factor by 1.0
      - Sending 'L' from the serial terminal decrease factor by 10.0
      - Sending 'h' from the serial terminal increase factor by 1.0
      - Sending 'H' from the serial terminal increase factor by 10.0
      - Sending 't' from the serial terminal call tare function
      - Sending 'T' from the serial terminal call big tare function
   - Observe and note the value of the new calibration factor
   - Use this new calibration factor in your sketch
*/

#include "FastRunningMedian.h"
#include <HampelFilter.h>
HampelFilter tareHampel = HampelFilter(0.00, 19, 0.02);
FastRunningMedian<uint32_t, 19, 0> tareMedian;
#include <HX711_ADC.h>
// I modified the settings in config.h as follows:
// SAMPLES 64
// IGN_HIGH_SAMPLE 1
// IGN_LOW_SAMPLE 0

#define scale_DATA 0
#define scale_SCLK 1
#define scale_PWDN 2
#define scale_SPEED 22

//HX711 constructor (dout pin, sck pin)
HX711_ADC LoadCell(scale_DATA, scale_SCLK);

long t;

void setup() {
  Serial.begin(115200);

  pinMode(scale_PWDN, OUTPUT);
  digitalWrite(scale_PWDN, HIGH);    // keep high to stay on
  pinMode(scale_SPEED, OUTPUT);
  digitalWrite(scale_SPEED, LOW);    // keep high for high speed

  delay(300);
  Serial.println("preparing...");
  LoadCell.begin();
  long stabilisingtime = 5000; // tare preciscion can be improved by adding a few seconds of stabilising time
  LoadCell.start(stabilisingtime);
  LoadCell.setCalFactor(25830.0f); // user set calibration factor (float)
  LoadCell.setTareOffset(8380000);
  Serial.println("Startup + tare is complete");
}

void loop() {
  //update() should be called at least as often as HX711 sample rate; >10Hz@10SPS, >80Hz@80SPS
  //longer delay in scetch will reduce effective sample rate (be carefull with delay() in loop)
  LoadCell.update();

  //get smoothed value from data set + current calibration factor
  if (millis() > t + 250) {
    float i = LoadCell.getData();
    float v = LoadCell.getCalFactor();
    Serial.print("Load_cell output val: ");
    Serial.print(i);
    Serial.print("      Load_cell calFactor: ");
    Serial.println(v);
    t = millis();
  }

  //receive from serial terminal
  if (Serial.available() > 0) {
    float i;
    char inByte = Serial.read();
    if (inByte == 'l') i = -1.0;
    else if (inByte == 'L') i = -10.0;
    else if (inByte == 'h') i = 1.0;
    else if (inByte == 'H') i = 10.0;
    else if (inByte == 'T') multiple_tare();
    else if (inByte == 't') LoadCell.tareNoDelay();
    if (i != 't') {
      float v = LoadCell.getCalFactor() + i;
      LoadCell.setCalFactor(v);
    }
  }

  //check if last tare operation is complete
  if (LoadCell.getTareStatus() == true) {
    Serial.print("Tare offset: ");
    Serial.println(LoadCell.getTareOffset());
  }
}

void multiple_tare() {
  Serial.println("wait, calculating... this will take long... countdown:");
  for (int i = 0; i < 20; i++) {
    Serial.println(20 - i);
    delay(250);
    LoadCell.tare();
    uint32_t value = LoadCell.getTareOffset();
    tareMedian.addValue(value);
    double value_f = double(value) / double(2500000);
    tareHampel.write(value_f);
  }
  Serial.print("Tare by runningMedian: ");
  Serial.println(tareMedian.getMedian());
  Serial.print("Tare by HampelFilter: ");
  Serial.println(2500000 * tareHampel.readMedian());
  Serial.print("Tare by both filters: ");
  double tare_offset = 0.5 * (tareMedian.getMedian() + 2500000 * tareHampel.readMedian());
  Serial.println(tare_offset);
  LoadCell.setTareOffset(tare_offset);
}