4-20 mA Unit with wemos S2 mini ESP32

obstbauer

Hello,
I want to use the 4-20 mA unit with a wemos S2 mini with ESP32 chip but I am not able to get some data from it.
I had a look at the github examples and made a program to show the current on a display. Display is working and I can find the unit with an i2c scanner.
Arduino gives no mistakes during compiling but it doesn`t work. Any ideas ?
Thank you

Here is my code:

#include <Wire.h>
#include <Arduino.h>
#include <U8g2lib.h>

#include "MODULE_4_20MA.h"

U8G2_SSD1309_128X64_NONAME2_F_HW_I2C u8g2(U8G2_R0,U8X8_PIN_NONE);

const byte led_gpio = 15;   // LED GPIO 15

MODULE_4_20MA cr;

void setup() {
  Wire.begin(33, 18);  // SDA pin 33, SCL pin 18
  u8g2.begin();
  pinMode(led_gpio, OUTPUT);
}
 
void loop() {
  float current = cr.getCurrentValue(0);

  u8g2.firstPage();
  do {

    u8g2.setFont(u8g2_font_ncenB10_tr);
    u8g2.drawStr(0,20,"Strom:");
    u8g2.setCursor(0, 40);
    u8g2.print(current);
  } while ( u8g2.nextPage() );
  
  digitalWrite(led_gpio, HIGH);
    delay(1000);
  digitalWrite(led_gpio, LOW);
  delay(1000);   
}

felmue

Hello @obstbauer

I think you might want to call cr.begin() in setup to set stuff like the proper I2C address for the library to use. See here.

Thanks
Felix

obstbauer

@felmue Hello,
thank you very much, it works !
I added

cr.begin(&Wire, MODULE_4_20MA_ADDR, 33, 18, 100000UL);

to void setup

obstbauer

it seems that I still have a problem....
I have a current reading but the value is wrong,
I get soemthing around 7.2 mA instead of 4 mA.
I can measure the 4 mA with a multimeter in the circuit and the sensor should send 4 mA, so this is ok, but the M5Stack unit shows 7.2 mA and I don't understand why ? Any ideas ?
My sensor is passive, I connected 24 V to the 4-20mA unit and all three jumpers are installed
What is the meaning of the function "getCalCurrent" ? It is neessary for the current measurement ? It is necessary to set a "ref current" ?

Thank you!

robski

@obstbauer try calibration function based on what you see with multimeter

obstbauer

@robski thanks for the answer

so you mean if I measure with multimter 4.0 mA (which is true for the sensor) and the unit shows me 7.2 mA I should set the calibrated value to 4.0 ?

Because this is not mentioned anywhere in a readme file or manual or in the description of the device, and it is not made in the example file at github
but I am a beginner....

robski

@obstbauer thats what i did with mine initially, calibrate with known current value

obstbauer

@robski ok I think I found it:

thank you I will try tomorrow

robski

@obstbauer yeah thats the registers table, I used Uiflow2 with calibration block but you are using not M5Stack controller I see

obstbauer

@robski what value do you take for "index" in the function

void MODULE_4_20MA::setCalCurrent(uint8_t index, uint16_t value)

robski

@obstbauer haven't used index value

in uiflow2 ..ain4_20ma_0.set_cal_current(10) to set 10mA
ain4_20ma_0.set_cal_current(20) to set 20mA

obstbauer

@robski yes maybe in uiflow2 but the function for the c program asks for an index and a value

obstbauer

I see really strange behaviour and I don't know the reason and I get no answers from the support.....
The example code from M5Stack say that the currentvalue should be divided by 100:

canvas.printf("Current:%.2fmA", (float)(meter.getCurrentValue(0)) / 100.0);

The values I get I have to divide by 10 to get the right current in mA.... and the other issue is that I can only use half of the measurement range, at 12.5 mA the ADC sends 65520...

maybe someone has an idea ?

obstbauer

change to a raspberry PI4 seems to be no solution too.....
it woud be nice if there would be a better documentation for people who want to use the units outside the m5stack universum....

robski

@obstbauer this is uiflow example with raw value and float too

obstbauer

thank you, but I am still not able to read out or to set the cal current
M5Stack support doesn`t answer my mails... and it seems that there is nobody from the company around here, I think I will change to another board with better support

robski

@obstbauer TBH if you are using M5Stack modules/units with not M5Stack controllers maybe its worth to have at least one M5Controller (atom?stick? )to be able to check module functionality