All sensors wrong reading

Hey, folks.
This is driving me mad. I bought a kit (IoT) to learn and make a final project (custom smart scale).
I started testing with DHT11 sensor. Wrong temperature reading. Looking online it seems that this is a shity sensor, so I put it aside and started playing with bmp180. It gives the same temperature as the DHT11. (Max diff is 0.8 celcius).
Please, bear in mind that this is with example code so, no code from my own.

I gave up playing with temperature and started building the scale. (50kg load cells + HX711 amplifier). Rewired it a dozen times and it always gives up erratic readings.

At this point the common point of failure is the board itself. So... here is my question:

Could the board itself being damaged, all sensors that are available with the kit plus the ones I bought (2 sets) are broken or is there something that I'm missing here?

Thanks for your time

Hello digo_santista

Have you read and studied the data sheets of the selected sensors with regard to measurement accuracy?

Have a nice day and enjoy coding in C++.

It is most likely to be your wiring layout. Did you change the layout or just keep doing the same thing over and over?

With sensitive things like temperature sensors it is best to use star wiring, that means that all the grounds are connected at one point and not chained one to the other, or series wiring.

In what way was it wrong?
How do you know it was "wrong"?

So its consistent. Surely thats good?

can you post the code please?

and tell us
1: the temperature value you expect
2: the data from the sensor, and
3: the temperature it is reporting

Yes. I have read the docs. I work as software developer, but my main language is Python. I'm familiar with documentation. From the top of my head, DHT11 sensors should have a 2 degree accuracy. I was expecting 12 degrees but got 20.

Worse for bmp180 since it's accuracy is supposed to be higher.

Load cells are supposed to be 150grams accurate. But it keeps going all over the place. (and I have read another post in this forum about those cells. didn't help and the post is already closed).

a board damaged but the board is still able to upload code and is still able to print values is very very unlikely.

There is a real high probality that this is a wiring or a code-problem.
This forum can be of great help. You have access to a lot of experience in coding and in electronics.

Though for really helping you must provide detail info
I'm a coding and electronic hobyist for very long now. I'm on this forum now for two years and have seen a lot of newcomers of all styles.

From this experience with a lot of newcomers I can tell:
make a fundamental descision
if you are willing to invest 10 to 50 hours into learning programming
if you are willing to invest 5 to 20 hours into learning electronics
start posting detail-information about your setup
as soon as you provide detail-information and as soon as you start asking specific questions the support will come and you will have fun learning it and having success step by step

If you are not willing to invest the time like described above
abandon the project and find a different thing as your "final project"

Anything in between is just waisting time.

The first step is to take 20 minutes time to read this

best regards Stefan

Yeah... When I started I had only the DHT11 sensor connected. That means it was sired straight to the board's ground.

I rewired the load cells in every configuration I could imagine. I followed the schematics on the bathroom scale from youtube video, but no luck.

And the load cells have room to flex.

For beeing really helpful you must provide a direct picture of how you have wired it
In a way that it is easy to see on the picture which wire is connected to what IO-pin on the microcontroller-board

1 Like

this code is for the temperature sensor comparison:

#include <Adafruit_BMP085.h>

/*************************************************** 
  This is an example for the BMP085 Barometric Pressure & Temp Sensor

  Designed specifically to work with the Adafruit BMP085 Breakout 
  ----> https://www.adafruit.com/products/391

  These pressure and temperature sensors use I2C to communicate, 2 pins
  are required to interface
  Adafruit invests time and resources providing this open source code, 
  please support Adafruit and open-source hardware by purchasing 
  products from Adafruit!

  Written by Limor Fried/Ladyada for Adafruit Industries.  
  BSD license, all text above must be included in any redistribution
 ****************************************************/

// Connect VCC of the BMP085 sensor to 3.3V (NOT 5.0V!)
// Connect GND to Ground
// Connect SCL to i2c clock - on '168/'328 Arduino Uno/Duemilanove/etc thats Analog 5
// Connect SDA to i2c data - on '168/'328 Arduino Uno/Duemilanove/etc thats Analog 4
// EOC is not used, it signifies an end of conversion
// XCLR is a reset pin, also not used here

#include <DFRobot_DHT11.h>
DFRobot_DHT11 DHT;
#define DHT11_PIN 10

Adafruit_BMP085 bmp;
  
void setup() {
  Serial.begin(115200);
  if (!bmp.begin()) {
	Serial.println("Could not find a valid BMP085 sensor, check wiring!");
	while (1) {}
  }
}
  
void loop() {
    Serial.print("BMP Temperature = ");
    float bmptemp = bmp.readTemperature();
    Serial.print(bmptemp);
    Serial.println(" *C");
    Serial.print("DHT11 Temperature = ");
    float temp = getDHT11temp();
    Serial.print(temp);

    float diff = bmptemp - temp;
    Serial.print("Temperature difference: ");
    Serial.print(diff);
    

    Serial.println();
    delay(1500);
}

and for the load cell is the example code:

/*
   -------------------------------------------------------------------------------------
   HX711_ADC
   Arduino library for HX711 24-Bit Analog-to-Digital Converter for Weight Scales
   Olav Kallhovd sept2017
   -------------------------------------------------------------------------------------
*/

/*
   This example file shows how to calibrate the load cell and optionally store the calibration
   value in EEPROM, and also how to change the value manually.
   The result value can then later be included in your project sketch or fetched from EEPROM.

   To implement calibration in your project sketch the simplified procedure is as follow:
       LoadCell.tare();
       //place known mass
       LoadCell.refreshDataSet();
       float newCalibrationValue = LoadCell.getNewCalibration(known_mass);
*/

#include <HX711_ADC.h>
#if defined(ESP8266)|| defined(ESP32) || defined(AVR)
#include <EEPROM.h>
#endif

//pins:
const int HX711_dout = 4; //mcu > HX711 dout pin
const int HX711_sck = 5; //mcu > HX711 sck pin

//HX711 constructor:
HX711_ADC LoadCell(HX711_dout, HX711_sck);

const int calVal_eepromAdress = 0;
unsigned long t = 0;

void setup() {
  Serial.begin(57600); delay(10);
  Serial.println();
  Serial.println("Starting...");

  LoadCell.begin();
  //LoadCell.setReverseOutput(); //uncomment to turn a negative output value to positive
  unsigned long stabilizingtime = 2000; // preciscion right after power-up can be improved by adding a few seconds of stabilizing time
  boolean _tare = true; //set this to false if you don't want tare to be performed in the next step
  LoadCell.start(stabilizingtime, _tare);
  if (LoadCell.getTareTimeoutFlag() || LoadCell.getSignalTimeoutFlag()) {
    Serial.println("Timeout, check MCU>HX711 wiring and pin designations");
    while (1);
  }
  else {
    LoadCell.setCalFactor(1.0); // user set calibration value (float), initial value 1.0 may be used for this sketch
    Serial.println("Startup is complete");
  }
  while (!LoadCell.update());
  calibrate(); //start calibration procedure
}

void loop() {
  static boolean newDataReady = 0;
  const int serialPrintInterval = 0; //increase value to slow down serial print activity

  // check for new data/start next conversion:
  if (LoadCell.update()) newDataReady = true;

  // get smoothed value from the dataset:
  if (newDataReady) {
    if (millis() > t + serialPrintInterval) {
      float i = LoadCell.getData();
      Serial.print("Load_cell output val: ");
      Serial.println(i);
      newDataReady = 0;
      t = millis();
    }
  }

  // receive command from serial terminal
  if (Serial.available() > 0) {
    char inByte = Serial.read();
    if (inByte == 't') LoadCell.tareNoDelay(); //tare
    else if (inByte == 'r') calibrate(); //calibrate
    else if (inByte == 'c') changeSavedCalFactor(); //edit calibration value manually
  }

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

}

void calibrate() {
  Serial.println("***");
  Serial.println("Start calibration:");
  Serial.println("Place the load cell an a level stable surface.");
  Serial.println("Remove any load applied to the load cell.");
  Serial.println("Send 't' from serial monitor to set the tare offset.");

  boolean _resume = false;
  while (_resume == false) {
    LoadCell.update();
    if (Serial.available() > 0) {
      if (Serial.available() > 0) {
        char inByte = Serial.read();
        if (inByte == 't') LoadCell.tareNoDelay();
      }
    }
    if (LoadCell.getTareStatus() == true) {
      Serial.println("Tare complete");
      _resume = true;
    }
  }

  Serial.println("Now, place your known mass on the loadcell.");
  Serial.println("Then send the weight of this mass (i.e. 100.0) from serial monitor.");

  float known_mass = 0;
  _resume = false;
  while (_resume == false) {
    LoadCell.update();
    if (Serial.available() > 0) {
      known_mass = Serial.parseFloat();
      if (known_mass != 0) {
        Serial.print("Known mass is: ");
        Serial.println(known_mass);
        _resume = true;
      }
    }
  }

  LoadCell.refreshDataSet(); //refresh the dataset to be sure that the known mass is measured correct
  float newCalibrationValue = LoadCell.getNewCalibration(known_mass); //get the new calibration value

  Serial.print("New calibration value has been set to: ");
  Serial.print(newCalibrationValue);
  Serial.println(", use this as calibration value (calFactor) in your project sketch.");
  Serial.print("Save this value to EEPROM adress ");
  Serial.print(calVal_eepromAdress);
  Serial.println("? y/n");

  _resume = false;
  while (_resume == false) {
    if (Serial.available() > 0) {
      char inByte = Serial.read();
      if (inByte == 'y') {
#if defined(ESP8266)|| defined(ESP32)
        EEPROM.begin(512);
#endif
        EEPROM.put(calVal_eepromAdress, newCalibrationValue);
#if defined(ESP8266)|| defined(ESP32)
        EEPROM.commit();
#endif
        EEPROM.get(calVal_eepromAdress, newCalibrationValue);
        Serial.print("Value ");
        Serial.print(newCalibrationValue);
        Serial.print(" saved to EEPROM address: ");
        Serial.println(calVal_eepromAdress);
        _resume = true;

      }
      else if (inByte == 'n') {
        Serial.println("Value not saved to EEPROM");
        _resume = true;
      }
    }
  }

  Serial.println("End calibration");
  Serial.println("***");
  Serial.println("To re-calibrate, send 'r' from serial monitor.");
  Serial.println("For manual edit of the calibration value, send 'c' from serial monitor.");
  Serial.println("***");
}

void changeSavedCalFactor() {
  float oldCalibrationValue = LoadCell.getCalFactor();
  boolean _resume = false;
  Serial.println("***");
  Serial.print("Current value is: ");
  Serial.println(oldCalibrationValue);
  Serial.println("Now, send the new value from serial monitor, i.e. 696.0");
  float newCalibrationValue;
  while (_resume == false) {
    if (Serial.available() > 0) {
      newCalibrationValue = Serial.parseFloat();
      if (newCalibrationValue != 0) {
        Serial.print("New calibration value is: ");
        Serial.println(newCalibrationValue);
        LoadCell.setCalFactor(newCalibrationValue);
        _resume = true;
      }
    }
  }
  _resume = false;
  Serial.print("Save this value to EEPROM adress ");
  Serial.print(calVal_eepromAdress);
  Serial.println("? y/n");
  while (_resume == false) {
    if (Serial.available() > 0) {
      char inByte = Serial.read();
      if (inByte == 'y') {
#if defined(ESP8266)|| defined(ESP32)
        EEPROM.begin(512);
#endif
        EEPROM.put(calVal_eepromAdress, newCalibrationValue);
#if defined(ESP8266)|| defined(ESP32)
        EEPROM.commit();
#endif
        EEPROM.get(calVal_eepromAdress, newCalibrationValue);
        Serial.print("Value ");
        Serial.print(newCalibrationValue);
        Serial.print(" saved to EEPROM address: ");
        Serial.println(calVal_eepromAdress);
        _resume = true;
      }
      else if (inByte == 'n') {
        Serial.println("Value not saved to EEPROM");
        _resume = true;
      }
    }
  }
  Serial.println("End change calibration value");
  Serial.println("***");
}

I was expecting around 12 degrees Celcius, but I'm getting from 19.9 to 21.9 (roughly... it varies if I approximate my hand).

Also, in warmer days (expecting 26 degrees) ended up getting 22...

For the load cells I Have always erratic values that keeps jumping all over the place

I was going to, but I'm using 2 load cells and wiring is a mess. I'll do my best to clear the way for the picture. Thanks.



Don't really know if it's possible to infer what I've done from those pictures. I only attached the loadcells wiring because those are the most complex one (and honestly, the only one I care about). The other ones are quiet simple.

Thanks

The HX711-board is a 24bit-resolution very high sensistive low-voltage-amplifying device.
The wires between loadcell and HX711board should be short
You are using very long wires and it is pretty likely that the long wires act as antennas that catch up too much electromagnetic noise which will change the measured value

The loadcell has wires maybe 20 cm long.
You should connect these wires directly to the HX711-board.
The interfacewires from HX711-board to the arduino can be longer but even there it will be better to keep them short.

So my suggestion is that you change your setup to have short wires everywhere connect one single loadcell and then run a test-code that is able to calibrate the load-cell.

best regards Stefan

1 Like

I tried with one cell and shorter cables. Now the readings are increasing steadily even wiht constant weight

post your actual and complete sketch

/*
   -------------------------------------------------------------------------------------
   HX711_ADC
   Arduino library for HX711 24-Bit Analog-to-Digital Converter for Weight Scales
   Olav Kallhovd sept2017
   -------------------------------------------------------------------------------------
*/

/*
   This example file shows how to calibrate the load cell and optionally store the calibration
   value in EEPROM, and also how to change the value manually.
   The result value can then later be included in your project sketch or fetched from EEPROM.

   To implement calibration in your project sketch the simplified procedure is as follow:
       LoadCell.tare();
       //place known mass
       LoadCell.refreshDataSet();
       float newCalibrationValue = LoadCell.getNewCalibration(known_mass);
*/

#include <HX711_ADC.h>
#if defined(ESP8266)|| defined(ESP32) || defined(AVR)
#include <EEPROM.h>
#endif

//pins:
const int HX711_dout = 4; //mcu > HX711 dout pin
const int HX711_sck = 5; //mcu > HX711 sck pin

//HX711 constructor:
HX711_ADC LoadCell(HX711_dout, HX711_sck);

const int calVal_eepromAdress = 0;
unsigned long t = 0;

void setup() {
  Serial.begin(57600); delay(10);
  Serial.println();
  Serial.println("Starting...");

  LoadCell.begin();
  //LoadCell.setReverseOutput(); //uncomment to turn a negative output value to positive
  unsigned long stabilizingtime = 2000; // preciscion right after power-up can be improved by adding a few seconds of stabilizing time
  boolean _tare = true; //set this to false if you don't want tare to be performed in the next step
  LoadCell.start(stabilizingtime, _tare);
  if (LoadCell.getTareTimeoutFlag() || LoadCell.getSignalTimeoutFlag()) {
    Serial.println("Timeout, check MCU>HX711 wiring and pin designations");
    while (1);
  }
  else {
    LoadCell.setCalFactor(1.0); // user set calibration value (float), initial value 1.0 may be used for this sketch
    Serial.println("Startup is complete");
  }
  while (!LoadCell.update());
  calibrate(); //start calibration procedure
}

void loop() {
  static boolean newDataReady = 0;
  const int serialPrintInterval = 0; //increase value to slow down serial print activity

  // check for new data/start next conversion:
  if (LoadCell.update()) newDataReady = true;

  // get smoothed value from the dataset:
  if (newDataReady) {
    if (millis() > t + serialPrintInterval) {
      float i = LoadCell.getData();
      Serial.print("Load_cell output val: ");
      Serial.println(i);
      newDataReady = 0;
      t = millis();
    }
  }

  // receive command from serial terminal
  if (Serial.available() > 0) {
    char inByte = Serial.read();
    if (inByte == 't') LoadCell.tareNoDelay(); //tare
    else if (inByte == 'r') calibrate(); //calibrate
    else if (inByte == 'c') changeSavedCalFactor(); //edit calibration value manually
  }

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

}

void calibrate() {
  Serial.println("***");
  Serial.println("Start calibration:");
  Serial.println("Place the load cell an a level stable surface.");
  Serial.println("Remove any load applied to the load cell.");
  Serial.println("Send 't' from serial monitor to set the tare offset.");

  boolean _resume = false;
  while (_resume == false) {
    LoadCell.update();
    if (Serial.available() > 0) {
      if (Serial.available() > 0) {
        char inByte = Serial.read();
        if (inByte == 't') LoadCell.tareNoDelay();
      }
    }
    if (LoadCell.getTareStatus() == true) {
      Serial.println("Tare complete");
      _resume = true;
    }
  }

  Serial.println("Now, place your known mass on the loadcell.");
  Serial.println("Then send the weight of this mass (i.e. 100.0) from serial monitor.");

  float known_mass = 0;
  _resume = false;
  while (_resume == false) {
    LoadCell.update();
    if (Serial.available() > 0) {
      known_mass = Serial.parseFloat();
      if (known_mass != 0) {
        Serial.print("Known mass is: ");
        Serial.println(known_mass);
        _resume = true;
      }
    }
  }

  LoadCell.refreshDataSet(); //refresh the dataset to be sure that the known mass is measured correct
  float newCalibrationValue = LoadCell.getNewCalibration(known_mass); //get the new calibration value

  Serial.print("New calibration value has been set to: ");
  Serial.print(newCalibrationValue);
  Serial.println(", use this as calibration value (calFactor) in your project sketch.");
  Serial.print("Save this value to EEPROM adress ");
  Serial.print(calVal_eepromAdress);
  Serial.println("? y/n");

  _resume = false;
  while (_resume == false) {
    if (Serial.available() > 0) {
      char inByte = Serial.read();
      if (inByte == 'y') {
#if defined(ESP8266)|| defined(ESP32)
        EEPROM.begin(512);
#endif
        EEPROM.put(calVal_eepromAdress, newCalibrationValue);
#if defined(ESP8266)|| defined(ESP32)
        EEPROM.commit();
#endif
        EEPROM.get(calVal_eepromAdress, newCalibrationValue);
        Serial.print("Value ");
        Serial.print(newCalibrationValue);
        Serial.print(" saved to EEPROM address: ");
        Serial.println(calVal_eepromAdress);
        _resume = true;

      }
      else if (inByte == 'n') {
        Serial.println("Value not saved to EEPROM");
        _resume = true;
      }
    }
  }

  Serial.println("End calibration");
  Serial.println("***");
  Serial.println("To re-calibrate, send 'r' from serial monitor.");
  Serial.println("For manual edit of the calibration value, send 'c' from serial monitor.");
  Serial.println("***");
}

void changeSavedCalFactor() {
  float oldCalibrationValue = LoadCell.getCalFactor();
  boolean _resume = false;
  Serial.println("***");
  Serial.print("Current value is: ");
  Serial.println(oldCalibrationValue);
  Serial.println("Now, send the new value from serial monitor, i.e. 696.0");
  float newCalibrationValue;
  while (_resume == false) {
    if (Serial.available() > 0) {
      newCalibrationValue = Serial.parseFloat();
      if (newCalibrationValue != 0) {
        Serial.print("New calibration value is: ");
        Serial.println(newCalibrationValue);
        LoadCell.setCalFactor(newCalibrationValue);
        _resume = true;
      }
    }
  }
  _resume = false;
  Serial.print("Save this value to EEPROM adress ");
  Serial.print(calVal_eepromAdress);
  Serial.println("? y/n");
  while (_resume == false) {
    if (Serial.available() > 0) {
      char inByte = Serial.read();
      if (inByte == 'y') {
#if defined(ESP8266)|| defined(ESP32)
        EEPROM.begin(512);
#endif
        EEPROM.put(calVal_eepromAdress, newCalibrationValue);
#if defined(ESP8266)|| defined(ESP32)
        EEPROM.commit();
#endif
        EEPROM.get(calVal_eepromAdress, newCalibrationValue);
        Serial.print("Value ");
        Serial.print(newCalibrationValue);
        Serial.print(" saved to EEPROM address: ");
        Serial.println(calVal_eepromAdress);
        _resume = true;
      }
      else if (inByte == 'n') {
        Serial.println("Value not saved to EEPROM");
        _resume = true;
      }
    }
  }
  Serial.println("End change calibration value");
  Serial.println("***");
}

It's just the calibration code without any changes.

The VERY, VERY, first step in debugging is to Serial.Print the RAW values from the A/D converter. Do not display any calculated results.
Then manually work through each of the calculations using the raw AD values and see if you get the correct answer for that sensor. If you manually get the correct answer, then fix the calculation. If still the wrong answer, suspect the sensor or it's power or it's Arduino connections.

Ok, so... This morning I decided to give the last try. Unplugged everything, got rid of the Dupont (?) connectors and soldered everything together.

Turns out, the readings were erratic for the load cell because the connections where not 100% with those connectors.

I was trying to avoid soldering as I'm not very skilled in that but I guess you live, you learn... that's it for the strain sensors. I'm still puzzled by the temperature sensor, though. I tried reconnecting straight to the board, but error of 10 degrees celsius still there. And they are the same error for both sensors...

nice to know that your temperature-readings are 10 !C above what it should be
frustrating that you did not provide enough details to give advice how to solve the problem

What type of temperature-sensor? Provide a link to the datasheet
post your complete sketch code that you use to measure temperatures
post what values you get in the serial monitor and post what the real temperature is

best regards Stefan

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