Esp 32 max9814 wrong reading

Projects General Guidance
1

hello everyone, i have project to measure amplitude, RT60 and SPL using max9814 connected with esp32. the data is then sent over to a websocket server, but it happens to have wrong readings. i will provide you with the code and i am hoping that someone will help me because i am a beginner in arduinoIDE, thank you all in advance.
""""CODE""""

#include <WiFi.h>
#include <ESPAsyncWebServer.h>
#include <ArduinoJson.h>
#include <arduinoFFT.h>

// Wi-Fi credentials
const char* ssid = "Monitor Sound";
const char* password = "12345678";

AsyncWebServer server(80);
AsyncWebSocket ws("/ws");

const int sampleRate = 1024; // Number of samples for FFT
double vReal[sampleRate];
double vImag[sampleRate];
const double samplingFrequency = 40000.0; // 40kHz sample rate
ArduinoFFT FFT = ArduinoFFT(vReal, vImag, sampleRate, samplingFrequency);

// Microphone calibration (example values)
const double micSensitivity = 0.02; // Sensitivity in V/Pa
const double referencePressure = 20e-6; // Reference pressure in Pascals

String htmlPage = R"rawliteral(

Sound Amplitude Graph let socket; let amplitude = 0, spl = 0, rt60 = 0; 
    function initWebSocket() {
        socket = new WebSocket(`ws://${location.hostname}/ws`);
        socket.onmessage = function (event) {
            const data = JSON.parse(event.data);
            amplitude = data.amplitude;
            spl = data.spl;
            rt60 = data.rt60;

            document.getElementById("amplitude").innerText = amplitude.toFixed(2);
            document.getElementById("spl").innerText = spl.toFixed(2);
            document.getElementById("rt60").innerText = rt60.toFixed(2);

            updateGraph(amplitude);
        };
    }

    let graphData = [];
    function updateGraph(newValue) {
        const canvas = document.getElementById("graph");
        const ctx = canvas.getContext("2d");

        // Normalize newValue to canvas height
        const normalizedValue = Math.min(canvas.height, Math.max(0, newValue / 100)); // Adjust scaling

        graphData.push(normalizedValue);
        if (graphData.length > canvas.width) {
            graphData.shift();
        }

        ctx.clearRect(0, 0, canvas.width, canvas.height);
        ctx.beginPath();
        ctx.moveTo(0, canvas.height - graphData[0]);
        graphData.forEach((val, index) => {
            ctx.lineTo(index, canvas.height - val);
        });
        ctx.stroke();
    }

    window.onload = function () {
        initWebSocket();
    };
</script>

Sound Amplitude Graph

Amplitude: 0

SPL: 0 dB

RT60: 0 seconds

)rawliteral";

void processFFT() {
for (int i = 0; i < sampleRate; i++) {
vReal[i] = analogRead(34); // Replace 34 with your ADC pin
vImag[i] = 0;
delayMicroseconds(25); // Adjust for proper sampling (40kHz)
}

FFT.windowing(FFT_WIN_TYP_HAMMING, FFT_FORWARD);
FFT.compute(FFT_FORWARD);
FFT.complexToMagnitude();

double amplitude = 0;
for (int i = 2; i < sampleRate / 2; i++) {
    amplitude = max(amplitude, vReal[i]);
}

// SPL Calculation
double spl = 20 * log10(amplitude * micSensitivity / referencePressure);

// RT60 Calculation using energy decay
double energyDecay[sampleRate / 2];
double totalEnergy = 0;
for (int i = 2; i < sampleRate / 2; i++) {
    totalEnergy += vReal[i] * vReal[i];
}

double currentEnergy = totalEnergy;
int decayIndex = 2;
while (decayIndex < sampleRate / 2 && currentEnergy > totalEnergy / 1000) {  // Approx -60 dB
    currentEnergy -= vReal[decayIndex] * vReal[decayIndex];
    decayIndex++;
}

double rt60 = (double)decayIndex / samplingFrequency;  // Time in seconds

StaticJsonDocument<200> jsonDoc;
jsonDoc["amplitude"] = amplitude;
jsonDoc["spl"] = spl;
jsonDoc["rt60"] = rt60;

String jsonString;
serializeJson(jsonDoc, jsonString);
ws.textAll(jsonString);

}

void onWebSocketEvent(AsyncWebSocket *server, AsyncWebSocketClient *client,
AwsEventType type, void *arg, uint8_t *data, size_t len) {
if (type == WS_EVT_CONNECT) {
Serial.printf("Client connected: %u\n", client->id());
} else if (type == WS_EVT_DISCONNECT) {
Serial.printf("Client disconnected: %u\n", client->id());
}
}

void setup() {
Serial.begin(115200);

WiFi.softAP(ssid, password);
IPAddress IP = WiFi.softAPIP();
Serial.print("Access Point started. IP address: ");
Serial.println(IP);

ws.onEvent(onWebSocketEvent);
server.addHandler(&ws);

server.on("/", HTTP_GET, [](AsyncWebServerRequest *request) {
    request->send_P(200, "text/html", htmlPage.c_str());
});

server.on("/favicon.ico", HTTP_GET, [](AsyncWebServerRequest *request) {
    request->send(404);
});

server.begin();

}

void loop() {
processFFT();
delay(100); // Adjust as needed for your application
}

""""WIRING"""""
esp32 D34 -> max9814 out
positive and negative rails are connected correctely

2

How long time does an alogRead take in that controller? I would be surpriced if that time is zero. This time adds to the delay of 25 mictoseconds, getting a lower sample frequency. I guess that could affect the FFT amgorithm.
Try some Serial.print yo be sure the analog reading works okey.

3

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