Deserialize JSON received from Serial port

Projects Programming
1

I wrote a Windows executable in C++ that reads sensor data from HWiNFO64, serializes the data and then sends it through a serial connection.

This is what I'm sending through the serial port

{"CPU [#0]: Intel Core i7-13700K: DTS":{"CPU Package":[{"Average":44.841623},{"Current":34.000000},{"Maximum":47.000000},{"Minimum":32.000000},{"Unit":"°C"}]}}

The data is being received correctly as shown in my photo, I'm just not why sure it didn't stop printing at the last character.
I tried with Serial.readStringUntil('\0') and with Serial.readString(), same result.
https://i.imgur.com/Vi9M1Nk.jpg

tft.setCursor(0, 0);
tft.print(Serial.readStringUntil('\0'));

I am not able to deserialize the data with ArduinoJson and I don't know what I'm doing wrong.
deserializeJson() always fails, so I left that part of the code commented out.

#define ARDUINOJSON_ENABLE_PROGMEM 0

#include <ArduinoJson.h>
#include <TFT_eSPI.h>

TFT_eSPI tft = TFT_eSPI();
const uint8_t rotation = 3;
const uint8_t textFont = 1;

uint16_t pollingRate = 1500;

String error;
void setup()
{
	tft.begin();
	tft.fillScreen(TFT_BLACK);
	tft.setRotation(rotation);
	tft.setTextFont(textFont);

	Serial.begin(576000);
	while (!Serial.available())
	{
		String message = F("COM port not connected");
		tft.setCursor(0, 36);
		tft.setTextColor(TFT_WHITE, TFT_RED);
		tft.print(message);
		error = message;
		delay(pollingRate);
	}
}

void loop()
{
	unsigned long epoch = millis();

	if (!Serial.available())
	{
		String message = F("COM port connection lost");
		if (error != message)
		{
			tft.fillScreen(TFT_RED);
			tft.setCursor(0, 36);
			tft.setTextColor(TFT_WHITE, TFT_RED);
			tft.print(message);
		}
		error = message;
		delay(pollingRate);
		return;
	}
/*
	const size_t capacity = JSON_ARRAY_SIZE(18) + 18*JSON_OBJECT_SIZE(6);
	DynamicJsonDocument json(capacity);

	DeserializationError jsonError = deserializeJson(json, Serial.readStringUntil('\0'));
	if (jsonError)
	{
		String message = F("Deserialize JSON failed");
		if (error != message)
		{
			tft.fillScreen(TFT_RED);
			tft.setCursor(CenterX(message), CenterY());
			tft.setTextColor(TFT_WHITE, TFT_RED);
			tft.print(message);
		}
		error = message;
		delay(pollingRate);
		return;
	}
*/
	if (!error.isEmpty())
	{
		error.clear();
		tft.fillScreen(TFT_BLACK);
	}
////////////////////////////////////////////
	tft.setCursor(0, 0);
	tft.setTextColor(TFT_WHITE, TFT_BLACK);
	tft.print(Serial.readStringUntil('\0'));
////////////////////////////////////////////
	unsigned long passed = (millis() - epoch);
	if (passed < pollingRate)
	{
		delay(pollingRate - passed);
	}
}

On the Windows side, this is how I am sending my serialized json string

Serial.WriteSerialPort(&json[0]);

I tried adding a terminating character, same result.

json += '\0';
Serial.WriteSerialPort(&json[0]);

I am doing something wrong with either the Serial port or the ArduinoJson library.
I'd be really thankful if someone could point out what I'm doing wrong.

2

On the windows side send the json

Serial.WriteSerialPort(const_cast<char*>(json.c_str()));

and then

Serial.WriteSerialPort('\n');

then on the arduino side I would suggest to study Serial Input Basics to handle this and use the '\n' as the end marker you are waiting for.

as a first start, to ensure the communication is working fine, write a simple arduino program echoing each character as it comes through

3

Compilation error:
sketch.ino:75:10: error: 'class String' has no member named 'clear'
reason.clear();
line 75 reason.clear();

Are you using arduino Uno, Mega, ........?

4

I'm using an ESP32.

5

I tried the example written by @Robin2 for receiving data with start and end markers and it only works correctly when I comment out the newData variable.

const byte numChars = 255;
char receivedChars[numChars];
//bool newData = false;

void loop()
{
	unsigned long epoch = millis();

	static bool receiving = false;
	static byte receivedCharIndex = 0;
	char startMarker = '<';
	char endMarker = '>';
	char receivedChar;
	while (Serial.available() > 0/* && !newData*/)
	{
		receivedChar = Serial.read();
		if (receiving)
		{
			if (receivedChar != endMarker)
			{
				receivedChars[receivedCharIndex] = receivedChar;
				receivedCharIndex++;
				if (receivedCharIndex >= numChars)
				{
					receivedCharIndex = numChars - 1;
				}
			}
			else
			{
				receivedChars[receivedCharIndex] = '\0';
				receiving = false;
				receivedCharIndex = 0;
				//newData = true;
			}
		}
		else if (receivedChar == startMarker)
		{
			receiving = true;
		}
	}
	//if (newData)
	//{
		tft.setCursor(0, 0);
		tft.setTextColor(TFT_WHITE, TFT_BLACK);
		tft.print(receivedChars);
		//newData = false;
	//}

	unsigned long passed = (millis() - epoch);
	if (passed < pollingRate)
	{
		delay(pollingRate - passed);
	}
}

Windows:

string json = "<{";
//json += ...;
json += "}>";
Serial.WriteSerialPort(&json[0]);

I always get the correct output with the newData variable commented out.
https://i.imgur.com/CsvaGJf.png

But if I use the code without commenting out the newData variable, sometimes I get overlapped messages.
https://i.imgur.com/QeRDOg5.png

I created a web server on the ESP32 to help me visualize what is being received on the Serial port.

I am using my board's built-in CH340C to receive the data.

My goal is to send about 30000 characters of data from the computer to the ESP32 every 1500ms.

6

I made some small modifications to the sketch in the original post, but if .clear() doesn't compile use any other method to empty the String.

7

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