Mkr wifi 1010 loop speed improvement plan

Hardware MKR Family MKRWIFI1010
1

https://learn.sparkfun.com/tutorials/smart-home-expansion-kit-for-arduino-101/experiment-9-using-a-current-sensor

Unlike the link, I used mkr wifi 1010, sct-013-000. The rest of the configuration is the same.

The nocktime (t1-t2) being measured now is about 1290m/s, which is too long. I want to reduce this.

The sketches used are as follows.

#include "EmonLib.h"
EnergyMonitor emon1;

double Total = 0;
int count = 0;
double TotalPower = 0;
unsigned long t1 = 0;

void setup() {
  Serial.begin(9600);
  emon1.current(1, 111.1);

  for (int i = 0; i < 5; i++) {
    double IrmsNock = emon1.calcIrms(1480);
    if (IrmsNock < 0.2) {
      Total += IrmsNock;
      count++;
    }
  }

  Total /= count;
  Serial.print("Average IrmsNock: ");
  Serial.println(Total);

  t1 = millis();
}

void loop() {
  unsigned long t2 = millis();
  int nocktime = t2 - t1;
  t1 = t2;

  double Irms = emon1.calcIrms(1480) - Total;
  Irms = (Irms < 0) ? 0 : Irms;

  double power = Irms * 220.0;
  TotalPower += power * nocktime / 3600.0;

  Serial.print(nocktime);
  Serial.print("   Current: ");
  Serial.print(Irms, 4);
  Serial.print(" (A)   Power: ");
  Serial.print(power, 4);
  Serial.print(" (W)   Accumulated Power: ");
  Serial.print(TotalPower / 1000, 4);
  Serial.println(" (W)");
}

Q1. How to reduce nocktime

2

Don't use 1000 samples :wink: emon1.calcIrms() takes time because the analogRead()s take time; I do not know how fast analogRead() is on your board.

Please use code tags when posting code as described in How to get the best out of this forum.

3

Hello! Are you saying to reduce the number of samples?
Or do you want me to read it through analogread() and turn it into a current value?

4

That one.

You can do some testing how long an analogRead() takes. Something in the line of

void setup()
{
  Serial.begin(115200);
  while(!Serial);
  Serial.println("analogRead() speed test");
}

void loop()
{
  uint32_t sum = 0;
  uint32_t startTime = millis();
  for(uint16_t cnt=0; uint16_t <100; cnt++)
  {
    sum += analogRead(A0);
  }
  Serial.println("Average analogRead() time = ");
  Serial.println((millis() - startTime) / 100);
  Serial.print("Average value = ");
  Serial.println(sum/100);
}

Although sum is not strictly necessary, using it in a print statement prevents the compiler from optimising it away.

Not compiled, not tested.

On AVR based boards, an analogRead() takes roughly 100 microseconds; I know that a Due is a lot faster (can't remember how much).

Run the test to get a feel for the speed of analogRead().
And look at what calcIrms() in the EmonLib exactly does.

5

AnalogRead has a speed of about 1ms. I have a question here. How can I measure the power using analogRead()? The value of analogRead() has not changed.

6

That is very slow; there must be something wrong with your testing. As said, an AVR does a single analogRead() in approximately 100 microseconds and I expect your board to be a lot faster.

I do not understand. I did not say that you had to use analogRead(); I just needed you to understand where the slowness of your code comes from.

Did you have a look at what calcIrms() does? It simply uses analogRead().

double EnergyMonitor::calcIrms(unsigned int Number_of_Samples)
{

  #if defined emonTxV3
    int SupplyVoltage=3300;
  #else
    int SupplyVoltage = readVcc();
  #endif


  for (unsigned int n = 0; n < Number_of_Samples; n++)
  {
    sampleI = analogRead(inPinI);

    // Digital low pass filter extracts the 2.5 V or 1.65 V dc offset,
    //  then subtract this - signal is now centered on 0 counts.
    offsetI = (offsetI + (sampleI-offsetI)/1024);
    filteredI = sampleI - offsetI;

    // Root-mean-square method current
    // 1) square current values
    sqI = filteredI * filteredI;
    // 2) sum
    sumI += sqI;
  }

  double I_RATIO = ICAL *((SupplyVoltage/1000.0) / (ADC_COUNTS));
  Irms = I_RATIO * sqrt(sumI / Number_of_Samples);

  //Reset accumulators
  sumI = 0;
  //--------------------------------------------------------------------------------------

  return Irms;
}

According to the processor datasheet, the processor on your board can achieve 350 ks/s, so roughly 3 microseconds for a sample.

I do not know the processor on your board. You can change the resolution using analogReadResolution() - Arduino Reference; a lower resolution should speed up the reading (but you will never reach the theoretical maximum).

7

I'm so sorry. The main point of my comment was that I have to send the power value (W) every 0.1 seconds, and the nocktime was too long.

8

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