[Solved] ESP8266 WiFi: Inaccurate temperature values after decimal point - 28.50 instead of 28.18

slowik359 wrote:

why does it display to me not the exact decimal value in esp8266 wifi e.g. 28.50 ,34.00 ,25.50 ,22.50 and before it was 34.12 or 28.18 https://obrazki.elektroda.pl/2611699600_1694342459.png

Welcome to the forum!

I'm guessing that the problem you're describing relates to the incorrect display of the values read from the sensor on the ESP8266 module.

It appears that the values are rounded to the nearest .50 or .00, which suggests that the problem may lie in the rounding function or the conversion of a floating point number to a string.

But before we go any further, additional information is needed:

1. What sensor are you using for the measurements?
2. What is the code that reads the values from the sensor and displays them?
3. Have you made any changes to the code, hardware or settings that could cause this problem?
4. Does the problem occur regardless of which value you are trying to read?

In most cases, the incorrect display of the result could be due to an incorrect conversion of a floating point number to a string (or vice versa), an error in the rounding function, or a problem with the precision of the calculation on the microcontroller.

Please provide the above information so that we can better understand and help you solve this problem.

slowik359 wrote:

(...) t width height temp
display.println(temp);
display.println(" ");
display.drawRect(123,30, 5, 5, WHITE); // this is from the celsius sign
display.setCursor(110,25);
display.setFont();
display.display();
Blynk.virtualWrite(V2, temp); //sending to Blynk app



delay(5000);
}

Thanks for providing the full code again. It seems correct and should not cause problems with rounding to .50 or .00. The DallasTemperature library you are using returns the temperature as a `float`, so you should get a full precision reading.

However, I noticed that you are using `display.println(temp);` to print the temperature to the display. By default, the `println()` function for the `float` type (as in the case of your `temp` variable) will only print two decimal places, which seems to be what you are seeing.

Also, the `println()` method rounds floating-point numbers rather than truncates them, which may explain why you only see .50 or .00 - this is due to rounding.

You could try using the `dtostrf()` function to convert `float` to `char[]` with the specified precision, and then print this string to the display. Below is an example of how to do this:



The `dtostrf()` function converts a floating point value to a string. The second argument is the minimum width of the field, the third argument is the precision of the number (number of decimal places), and the last argument is the buffer for the result.

Values greater than 99.99 or less than -9.99 will look slightly different because their length has exceeded 4 places. You can adjust the second argument of `dtostrf()` to match the longest expected number.

Hopefully this solves the problem. Let me know if you need any more help!

slowik359 wrote:

(...) t width height temp
display.println(temp);
display.println(" ");
display.drawRect(123,30, 5, 5, WHITE); // this is from the celsius sign
display.setCursor(110,25);
display.setFont();
display.display();
Blynk.virtualWrite(V2, temp); //sending to Blynk app


delay(5000);
}

I noticed that despite using `dtostrf(temp, 4, 2, temp_display);` in your code, you still call `display.println(temp);` to display the temperature. This line will print the `float` value of temp, not the converted `temp_display` string.

I suggest changing this part to `display.println(temp_display);` to print the converted string, which should contain the full temperature precision. Here is the modified code snippet:



At the end I changed `display.println(temp);` to `display.println(temp_display);` in order to use the converted string instead of the original floating point value. This way you should see the full precision of the temperature on the display.

slowik359 wrote:

it didn't help because on the test one with the arduino it is the same maybe the sensor is dead

I guess when you say "on the test one with the arduino it is the same", you are trying to use a different microcontroller to test the same sensor? If so, and you still see the same results, it is possible that the problem actually lies with the DS18B20 sensor.

The DS18B20 sensors are usually quite reliable, but like any device, they can fail.

Remember that the DS18B20 is a digital sensor and returns temperature as a 16-bit number in binary format, so almost all possible values should be available. Limiting the results to values ending in .00 and .50 is very unusual and not typical of these sensors.

Before assuming that the sensor is faulty, however, it is worth checking a few things:
1. Check that the circuit is correctly powered and connected. The DS18B20 operates on a voltage between 3.0V and 5.5V. Make sure that the supply voltage is stable and within this range.
2. Check that you have correctly connected the "pull-up" resistor to the data line. Typically, a resistor between 4.7k Ohm and 10k Ohm is recommended for the DS18B20.
3. Try reading the temperature with another DS18B20 sensor (if you have one) to see if the problem occurs with other sensors as well.
4. Try testing your sensor with simple code that only reads and displays the temperature, with no additional libraries or functions. Does the problem still occur?

Remember that each sensor has its own specific operation and this may vary slightly from manufacturer to manufacturer. In some cases, sensors may need additional calibration to ensure accurate readings.

If the problem persists despite attempts to solve it, it is likely that the sensor is actually faulty and you should replace it.

slowik359 wrote:

The problem may lie in the fact that I have flashing it several times with the espe tool I don't know if I did it right maybe you need to do it again could you provide what and how

Flashing the ESP8266 is the process of writing new firmware to the microcontroller. If you suspect the problem lies with this, it may be worth trying to re-flash the microcontroller. Below are the steps you should take. I use a tool called "esptool" for this.


Please note - The steps below are for the Windows operating system.

Step 1 : Download and install the latest version of Python from the official Python website.

Step 2 : Open cmd (Command Prompt) and install esptool using the following command:




Step 3 : Connect the ESP8266 module to your computer using the USB cable. Then, using Device Manager, check under which COM port your ESP8266 module is connected.

Step 4 : Now we need to clear the ESP8266 flash memory. To do this, type the following command into cmd, replacing "COMX" with the appropriate COM port number:




Step 5 : Now we can reflash our ESP8266 module. To do this, we need to download the appropriate firmware binary file. This can be found on the official NodeMCU website. After downloading the file, enter the following command into cmd:




Place "COMX" with your COM port number and "path_to_file_binary" with the path to the downloaded binary file.

Assuming everything went well, you should now have the ESP8266 module flashed. You can now try running your code again and see if the problem still exists.

slowik359 wrote:

I may not be familiar with this binary file

I understand that you may be having trouble finding the correct firmware file for your ESP8266 module. Let me help you.

Firmware updates for the ESP8266 module are available on the ESP8266 Community project page on GitHub. Below is a link to the latest releases:

[ESP8266 releases on GitHub](https://github.com/esp8266/Arduino/releases)

On this page you will see a list of different releases. The latest one is the most recent one. Click on it and then scroll down the page until you see the "Assets" section. This is where you will find the firmware binaries.

The files are named "esp8266-xxxxxx.zip". Download the latest .zip file and then unzip it. Inside, you should find the .bin file you need to perform the flashing process.

Memorize to modify the above command appropriately to include the correct path to the binary file on your computer.

If you still have problems finding the file or with the flashing process, please let me know. I will be happy to help you through the process step by step.

slowik359 wrote:

I cannot know this binary file

It looks like you are still having problems finding the binary file. I apologise for any confusion. Please let me direct you more accurately.


Download the latest ESP8266 firmware

The first step is to download the latest firmware for the ESP8266. You can download it directly from the official GitHub page of the ESP8266 project. Here is the direct link to the firmware release page:

[https://github.com/esp8266/Arduino/releases](https://github.com/esp8266/Arduino/releases)


How to find the binary file on the release page

When you get to the release page, scroll down to the "Assets" section. There you will find various files to download. Look for the file that ends in ".bin" - this is the firmware binary file you need to download.

For example, for release 2.7.4, the binary file is called "esp8266-2.7.4.bin". Click on this file to download it.


Where are downloaded files saved

After downloading the file, it should be in the "Downloaded" directory on your computer, unless you have changed the default download settings in your browser.


How to find the path to the binary file

To find the path to the binary file, open the "Downloaded" directory and find the downloaded file. Right-click on the file and select "Properties". In the "Location" section, you will find the full path to the file.

Provide this path when flashing the ESP8266, replacing "path_to_binary_file" in step 5 of my previous instructions.

If you still encounter problems, please let me know! I will be happy to help you through the process.