vehicle-monitor/ESP32/vehicle-monitor.cpp

#include <Arduino.h>

#include <WiFi.h>
#include <FS.h>
#include <SPIFFS.h>
#include <ESPAsyncWebServer.h>

#include "wifi-credentials.h"

AsyncWebServer server(80);

float averageBatteryVoltage = 0.0f;
int16_t batteryVoltage = -1; //in mV

struct ADC_CalibrationValue
{
	float Measure;
	int16_t ADC_Value;
};

const ADC_CalibrationValue calibration[] = {
	{ 0.118f,	1 },
	{ 0.343f, 	253 },
	{ 0.791f, 	801 },
	{ 1.512f, 	1705 },
	{ 2.013f,	2306 },
	{ 2.406f,	2796 },
	{ 2.606f,	3058 },
	{ 2.839f,	3423 },
	{ 2.996f,	3726 },
	{ 3.16f,	4094 }
};
const int8_t calibrationNumValues = sizeof(calibration)/sizeof(calibration[0]);

float getCalibratedVoltage(int16_t adcOutput)
{
	for(int8_t i = 1; i < calibrationNumValues; ++i)
	{
		if(i == calibrationNumValues - 1 || calibration[i].ADC_Value >= adcOutput)
		{
			const auto& p = calibration[i - 1];
			const auto& n = calibration[i];
			return (float)(adcOutput - p.ADC_Value) / (float)(n.ADC_Value - p.ADC_Value) * (n.Measure - p.Measure) + p.Measure;
		}
	}

	return -1.0f;
}

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

	if(!SPIFFS.begin(false)){
		Serial.println("SPIFFS Mount Failed");
		return;
	}

	// Connect to Wi-Fi
	WiFi.begin(wifi_ssid, wifi_password);
	while (WiFi.status() != WL_CONNECTED)
	{
		delay(1000);
		Serial.println("Connecting to Wifi...");
	}

	// Print ESP Local IP Address
	Serial.print("Wifi connected, ip=");
	Serial.println(WiFi.localIP());

	server.on("/api/status", HTTP_GET, [](AsyncWebServerRequest *request){
		int v = batteryVoltage;
		char json[128];
		sprintf(json, "{\"v\":%d,\"c\":1000}", v);
		request->send(200, "text/json", json);
	});

	// Special case to send index.html without caching
	server.on("/", HTTP_GET, [](AsyncWebServerRequest *request){ request->send(SPIFFS, "/www/index.html", "text/html"); });
	server.serveStatic("/index.html", SPIFFS, "/www/index.html");

	// Other static files are cached (index.html knows whether to ignore caching or not for each file)
	server.serveStatic("/", SPIFFS, "/www/").setCacheControl("max-age=5184000");

	server.begin();
	Serial.println("HTTP server started");
}

float avgAnalogV = 0.0f;

void loop()
{
	const int potPin = 34;

	const float minV = 0.14f; // 1
	const float maxV = 3.16f; // 4094

	delay(10);
	int16_t analogV = analogRead(potPin);
	float v = getCalibratedVoltage(analogV);

	averageBatteryVoltage = averageBatteryVoltage * 0.95f + v * 0.05f;
	batteryVoltage = (int16_t)(averageBatteryVoltage * 1000.0f + 0.5f);

	//avgAnalogV = avgAnalogV * 0.9f + (float)analogV * 0.1f;
	//batteryVoltage = (int16_t)(avgAnalogV + 0.5f);
}