using UDP to receive ESP32 sensor data by json format

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jun
jun 2024-11-28
编辑： Walter Roberson 2024-11-29
I want to using matlab to receive Esp32 data by UDP , UDP is fast.
I just code a test program which I send command to esp32 to return a sine wave , freq and sample is sent by matlab to esp32. My program works well when the total sample is under 160, it gives me the result I expected. But when I add the sample number, the UDP communication failed.
esp32 works seems correctly, I monitered the data by serial data port .
My program is following:
%% initialise UDP
% ESP32 IP and port
global ALLOVER;
global buffer;
global bufferTotal;
esp32IP = '192.168.1.52'; % ESP32 IP
esp32Port = 12345;
udpObj = udpport("datagram", "IPV4");
configureCallback(udpObj,"datagram",1,@readMyData)
disp('UDP start');
% send command to esp32
Freq = 10; % frequency
LengthSample = 150; % total sample number
command = struct('command', 'collect_data', 'length', LengthSample, 'frequency', Freq);
jsonCommand = jsonencode(command);
write(udpObj, jsonCommand, "string", esp32IP, esp32Port);
disp(['command sent out: ', jsonCommand]);
% receiving data
disp("reveive data...");
buffer = ""; % empty buffer
bufferTotal=0;
ALLOVER=false;
while (true)
if (ALLOVER==false)
pause(0.1);
else
break;
end
end
%
% delete the "END"
buffer = erase(buffer, "END");
% get sample from JSON
try
receivedData = jsondecode(buffer);
value = receivedData.values;
% draw sine wave
figure(1);
samplingInterval = 5; % ms
time = (0:length(value)-1) * samplingInterval;
plot(time, value, 'LineWidth', 1.5);
xlabel('Time (ms)');
ylabel('Amplitude');
title('Received Signal');
grid on;
disp('draw finish');
catch ME
disp('JSON fail：');
disp(ME.message);
end
function readMyData(u, ~)
% UDP
global buffer;
global ALLOVER;
global bufferTotal;
bufferTotal=bufferTotal+1;
packet = read(u, 1, "string");
buffer = buffer + string(packet.Data); % over 1 package
disp("receive data：");
disp(packet.Data); %
% find "END"
if contains(buffer, "END")
disp("Found 'END'，whole data ");
ALLOVER=true;
end
end
esp32 program is following:
#include <WiFi.h>
#include <AsyncUDP.h>
#include <ArduinoJson.h>
const char* ssid = "ws0922902";
const char* password = "13201604223";
AsyncUDP udp;
void setup() {
Serial.begin(115200);
// WiFi
WiFi.begin(ssid, password);
while (WiFi.status() != WL_CONNECTED) {
delay(1000);
Serial.println("conneting with WiFi ...");
}
Serial.println("WiFi is connected");
Serial.println(WiFi.localIP());
// UDP
if (udp.listen(12345)) {
Serial.println("UDP has started");
udp.onPacket([](AsyncUDPPacket packet) {
Serial.print("command received: ");
Serial.println((char*)packet.data());
// JSON
StaticJsonDocument<200> doc;
DeserializationError error = deserializeJson(doc, packet.data());
if (error) {
Serial.println("JSON format failure");
return;
}
String command = doc["command"];
int length = doc["length"];
int frequency = doc["frequency"];
if (command == "collect_data") {
// generate sine wave
float data[length];
for (int i = 0; i < length; i++) {
data[i] = sin(2 * PI * frequency * (i * 0.005)); // 5 ms sample
}
// send by JSON
StaticJsonDocument<2048> response;
//JsonArray timeArray = response.createNestedArray("time");
JsonArray valuesArray = response.createNestedArray("values");
for (int i = 0; i < length; i++) {
valuesArray.add(data[i]); //
}
String responseData;
serializeJson(response, responseData);
responseData += "END";
packet.printf(responseData.c_str());
Serial.println("data has sent out");
Serial.printf(responseData.c_str());
}
});
}
}
void loop() {
// nothing
}

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采纳的回答

jun
jun 2024-11-29
I have found the problem that is when esp32 send the UDP package over 1500, some data is lost, so the END will never be detected in matlab . rewrite esp32 be sure max number of sent is less than 1400, if over, send several times.
...................................
const int MAX_PACKET_SIZE = 1400; // Max payload size to fit within MTU
............................
responseData += "END";
// Send the response in smaller packets
int totalLength = responseData.length();
Serial.println("Sending data in chunks...");
for (int offset = 0; offset < totalLength; offset += MAX_PACKET_SIZE) {
String chunk = responseData.substring(offset, offset + MAX_PACKET_SIZE);
packet.printf(chunk.c_str(), chunk.length());
delay(10); // Allow receiver to process
}
Serial.println("Data sent successfully.");
Serial.printf(responseData.c_str());
}

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