esp8266-house-led-rgb/esp8266-house-led-rgb.ino

/*  Govee LED lights that were purcahsed from Amazon.com 100ft for 15USD.
 *  24Vdc 6 LED in series with current limiting resistor every 19.5".
 *  
 *            +----B----B----B----B----B----B----2K4-------------+
 *            |                                                  |
 *  24Vdc ----+----R----R----R----R----R----R----2K4-----------------+
 *            |                                                  |   |
 *            +----G----G----G----G----G----G----3K3---------------------+
 *            |                                                  |   |   |
 *            |                                                  |   |   |
 *            |                                                  |   |   |
 *            +---------+----B----B----B----B----B----B----2K4---+   |   |
 *                      |                                        |   |   |
 *                      +----R----R----R----R----R----R----2K4-------+   |
 *                      |                                        |   |   |
 *                      +----G----G----G----G----G----G----3K3-----------+
 *                      |                                        |   |   |
 *                      |                control bus:         blue  red  green
 *                      |                                        |   |   |
 *                      ...                                    ...  ...  ...
 *
 *  We installed about 150ft so about 90 led circuits will need power.  ESP8266 can
 *  do 1KHz PWM so we can use 3 pins if we want.  Another idea I had was to use lots
 *  of pins to control 20mA LED driver ICs.  With 15 pins one could make a circuit to
 *  drive 32 levels of current to each color giving 32,768 colors.  Each color would
 *  have 5 npn controlling 1,2,4,8,16 LED drivers.  One could then step through 0..620mA.
 *  
 *  Instead we will just use PWM to give us color control.  We just need to calculate how
 *  much current we want to send to our LED strip.  Because each circuit runs in parallel
 *  we need to determine how much current each branch will use.  The current limiting
 *  resistors means we can probably just use a fixed voltage supply.  With a 48Vdc supply
 *  at max brightness green will see 9mA, blue will see 12mA, and red will see 15mA.  These
 *  values are all pretty safe for the LED but the red would blow out a PN2222A with 1080mA.
 *
 *  We should be careful about the inductance of the wire.  Assuming 1/4mm diameter wire we
 *  might have 47uH.  We can use a diode on the collector of each color to send the spikes to
 *  the +48Vdc rail.  Each color will use an NPN-BJT, probably 3 parallel PN2222A with
 *  ballast resitors, as buffers for the PWM signal from the esp8266.
 *
 *  In the end I ended up using optoisolated pwm driving three power mosfets.  This ended
 *  up being a nuisance since the mosfet gates took forever to discharge resulting in
 *  the LEDs staying lit when the esp8266 pulled the signal down.  I did not really fix this
 *  but I did add a few resistors on the gate to bleed off the gate charge.  In effect the
 *  max brightness is 0xfc instead of 0xff since the led does not turn off on 0xfd.  But that
 *  is not really a deal-breaker, just annoying.
 *
 *  test using:
 *  curl -X POST http://rain-gutter-rgb.lan.rome7.com/rgb -d "color=010101"
 */
#include <ESP8266WiFi.h>
#include <WiFiClient.h>
#include <ESP8266WiFiMulti.h> 
#include <ESP8266mDNS.h>
#include <ESP8266WebServer.h>

ESP8266WiFiMulti wifiMulti;     // Create an instance of the ESP8266WiFiMulti class, called 'wifiMulti'

uint8_t hexStr[7] = "010101";

/*  131 allows for frame count, 16 colors(3), 16 transistions(1), and a null terminator
 *  the user provides the input as utf-8 encoded hexidecimal, we need twice
 *  the storage space, but parsing is a little easier: 2 + (2 * (3 * 16 + 16)) + 1 = 131
 *  [?] there are 16 transistions because there is an extra transition when we
 *      reach the end an loop to the begining
 *  [?] frame count allows user to have an animation that is not the maximum length,
 *      as of this note, the max frame count is 0x0f, '0f' when using a
 */
#define HOW_MANY_ANIMATION_FRAMES 16
#define MAX_ANIMATE_FRAME_COUNT_LEN 2
#define NULL_TERMINATOR_LEN 1
#define FRAME_LEN (3 + 1)
#define ANIMATE_BUFFER_LEN (MAX_ANIMATE_FRAME_COUNT_LEN + (2 * HOW_MANY_ANIMATION_FRAMES * FRAME_LEN) + NULL_TERMINATOR_LEN)
#define MAX_ANIMATE_FRAME_COUNT ((ANIMATE_BUFFER_LEN - 2 - 1) / 8)
uint8_t animateStr[ANIMATE_BUFFER_LEN];
uint8_t animate = 0;

uint8_t red = 1;
uint8_t green = 1;
uint8_t blue = 1;
uint8_t brightness = 50;

#define DISABLE_FASTLED_CORRECTION 0
#define ENABLE_FASTLED_CORRECTION 1
#define DISABLE_GAMMA_CORRECTION 0
#define USE_PHILIP_GAMMA_CORRECTION 1
#define USE_BG100_S_CURVE_GAMMA_CORRECTION 2

uint8_t gammaCorrectionType = DISABLE_GAMMA_CORRECTION;
uint8_t useFastLedCorrection = DISABLE_FASTLED_CORRECTION;

// quick fix for gamma correction from Adafruit's Phillip Burgess
static uint8_t phillip_adafruitGamma8[] = {
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  1,  1,  1,  1,
    1,  1,  1,  1,  1,  1,  1,  1,  1,  2,  2,  2,  2,  2,  2,  2,
    2,  3,  3,  3,  3,  3,  3,  3,  4,  4,  4,  4,  4,  5,  5,  5,
    5,  6,  6,  6,  6,  7,  7,  7,  7,  8,  8,  8,  9,  9,  9, 10,
   10, 10, 11, 11, 11, 12, 12, 13, 13, 13, 14, 14, 15, 15, 16, 16,
   17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, 23, 24, 24, 25,
   25, 26, 27, 27, 28, 29, 29, 30, 31, 32, 32, 33, 34, 35, 35, 36,
   37, 38, 39, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 50,
   51, 52, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 66, 67, 68,
   69, 70, 72, 73, 74, 75, 77, 78, 79, 81, 82, 83, 85, 86, 87, 89,
   90, 92, 93, 95, 96, 98, 99,101,102,104,105,107,109,110,112,114,
  115,117,119,120,122,124,126,127,129,131,133,135,137,138,140,142,
  144,146,148,150,152,154,156,158,160,162,164,167,169,171,173,175,
  177,180,182,184,186,189,191,193,196,198,200,203,205,208,210,213,
  215,218,220,223,225,228,231,233,236,239,241,244,247,249,252,255 };

// another implementation of gamma correction produced by bg100: f(x) = 1/(1+EXP(((A2/21)-6)*-1))*255
static uint8_t bg100_sCurveGamma8[] = {
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
  0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02,
  0x02, 0x02, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x04, 0x04, 0x04, 0x04, 0x04, 0x05, 0x05, 0x05,
  0x05, 0x06, 0x06, 0x06, 0x07, 0x07, 0x07, 0x08, 0x08, 0x08, 0x09, 0x09, 0x0A, 0x0A, 0x0B, 0x0B,
  0x0C, 0x0C, 0x0D, 0x0D, 0x0E, 0x0F, 0x0F, 0x10, 0x11, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
  0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1F, 0x20, 0x21, 0x23, 0x24, 0x26, 0x27, 0x29, 0x2B, 0x2C,
  0x2E, 0x30, 0x32, 0x34, 0x36, 0x38, 0x3A, 0x3C, 0x3E, 0x40, 0x43, 0x45, 0x47, 0x4A, 0x4C, 0x4F,
  0x51, 0x54, 0x57, 0x59, 0x5C, 0x5F, 0x62, 0x64, 0x67, 0x6A, 0x6D, 0x70, 0x73, 0x76, 0x79, 0x7C,
  0x7F, 0x82, 0x85, 0x88, 0x8B, 0x8E, 0x91, 0x94, 0x97, 0x9A, 0x9C, 0x9F, 0xA2, 0xA5, 0xA7, 0xAA,
  0xAD, 0xAF, 0xB2, 0xB4, 0xB7, 0xB9, 0xBB, 0xBE, 0xC0, 0xC2, 0xC4, 0xC6, 0xC8, 0xCA, 0xCC, 0xCE,
  0xD0, 0xD2, 0xD3, 0xD5, 0xD7, 0xD8, 0xDA, 0xDB, 0xDD, 0xDE, 0xDF, 0xE1, 0xE2, 0xE3, 0xE4, 0xE5,
  0xE6, 0xE7, 0xE8, 0xE9, 0xEA, 0xEB, 0xEC, 0xED, 0xED, 0xEE, 0xEF, 0xEF, 0xF0, 0xF1, 0xF1, 0xF2,
  0xF2, 0xF3, 0xF3, 0xF4, 0xF4, 0xF5, 0xF5, 0xF6, 0xF6, 0xF6, 0xF7, 0xF7, 0xF7, 0xF8, 0xF8, 0xF8,
  0xF9, 0xF9, 0xF9, 0xF9, 0xFA, 0xFA, 0xFA, 0xFA, 0xFA, 0xFB, 0xFB, 0xFB, 0xFB, 0xFB, 0xFB, 0xFC,
  0xFC, 0xFC, 0xFC, 0xFC, 0xFC, 0xFC, 0xFC, 0xFC, 0xFD, 0xFD, 0xFD, 0xFD, 0xFD, 0xFD, 0xFD, 0xFD,
  0xFD, 0xFD, 0xFD, 0xFD, 0xFD, 0xFD, 0xFD, 0xFE, 0xFE, 0xFE, 0xFE, 0xFE, 0xFE, 0xFE, 0xFF, 0xFF
}

/*  Fast-Led typical smd5050 led RGB color correction (0xFFB0F0 red 255, green 176, blue 240)
 *  measured brightness from typical LED vary by pn junction semiconductor material.
 *  
 *  [?] I am not too sure if this is measured by human eye or by device.  Human eyes have thee
 *      issues that need to be accounted for, one is the non-linear brightness that our nerves send
 *      to our brains.  Our eyes are more sensitive to green light.  The last problem is not really
 *      something we can handle in code as it in the realm of psychophysics, Weber–Fechner laws.  The
 *      Weber–Fechner has to do with the way our brains have a big impact on human perception.
 *      
 *  I believe that this color correction has to do with mechanical measurements as they are linear
 *  and I know that the human eye sensitivities are anything but.  Otherwise this is very crude.
 */
#define FASTLED_RED_CORRECTION    = 0x00FF;
#define FASTLED_GREEN_CORRECTION  = 0x00B0;
#define FASTLED_BLUE_CORRECTION   = 0x00F0;

uint8_t correctColor(uint8_t input, uint16_t factor) {
    uint16_t out;
    uint16_t in;
    in = input;
    out = in * factor;
    out /= 255;
    return ENABLE_FASTLED_CORRECTION == useFastLedCorrection
            ? gammaCorrection((uint8_t) out)
            : gammaCorrection(input);
}

uint8_t gammaCorrection(uint8_t input) {
    switch(gammaCorrectionType) {
        case USE_PHILIP_GAMMA_CORRECTION: return phillip_adafruitGamma8[input];
        case USE_BG100_S_CURVE_GAMMA_CORRECTION: return bg100_sCurveGamma8[input];
        case DISABLE_GAMMA_CORRECTION:
        default: 
    }
    return input;
}



ESP8266WebServer server(80);    // Create a webserver object that listens for HTTP request on port 80

void handleRoot();              // function prototypes for HTTP handlers
void handleLogin();
void handleNotFound();

void setup(void){
  Serial.begin(115200);         // Start the Serial communication to send messages to the computer
  delay(10);
  Serial.println('\n');

  wifiMulti.addAP("n-phone-number-upstairs", "3103229909cedar");   // add Wi-Fi networks you want to connect to
  wifiMulti.addAP("n-phone-number", "3103229909cedar");

  Serial.println("Connecting ...");
  int i = 0;
  while (wifiMulti.run() != WL_CONNECTED) { // Wait for the Wi-Fi to connect: scan for Wi-Fi networks, and connect to the strongest of the networks above
    delay(250);
    Serial.print('.');
  }
  Serial.println('\n');
  Serial.print("Connected to ");
  Serial.println(WiFi.SSID());               // Tell us what network we're connected to
  Serial.print("IP address:\t");
  Serial.println(WiFi.localIP());            // Send the IP address of the ESP8266 to the computer
  /*
  if (MDNS.begin("rain-gutter-rgb")) {              // Start the mDNS responder for esp8266.local
    Serial.println("mDNS responder started");
  } else {
    Serial.println("Error setting up MDNS responder!");
  }
  */
  server.on("/", HTTP_GET, handleRoot);        // Call the 'handleRoot' function when a client requests URI "/"
  //server.on("/login", HTTP_POST, handleLogin); // Call the 'handleLogin' function when a POST request is made to URI "/login"
  server.on("/rgb", HTTP_POST, handleRGB); // Call the 'handleRGB' function when a POST request is made to URI "/login"
  server.on("/dec", HTTP_GET, handleGetDec);
  server.on("/echo", HTTP_GET, handleEchoHex);
  server.on("/animate", HTTP_GET, handleAnimate);
  server.on("/cfg", HTTP_GET, handleGetCfg);
  server.on("/cfg", HTTP_POST, handleCfg);
  server.on("/brightness", HTTP_POST, handleGetBrightness);
  server.on("/brightness", HTTP_POST, handleBrightness

  server.onNotFound(handleNotFound);           // When a client requests an unknown URI (i.e. something other than "/"), call function "handleNotFound"

  server.begin();                            // Actually start the server
  Serial.println("HTTP server started");

  /* esp8266 12-f breakout board has pins mapped a bit odd, and arduino esp8266 libs use GPIO pin number */
  #define PIN_5 14 /* GPIO_14 */
  #define PIN_6 12 /* GPIO_12 */
  #define PIN_7 13 /* GPIO_13 */

  /*  slowing the PWM frequency decreases the error caused by the power mosfets
   *  having a slow turn-off
   *  this comes at a cost of flickering.  One might think that LED PWM at
   *  1000Hz is not noticeable by the human eye, but one can see the flicker
   *  appear as multiple spots when moving.  It isn't really a flicker but one
   *  can tell.
   */
  //analogWriteFreq(1000);
  analogWriteFreq(250);

  // lower brightness to minimal value
  brightness = 0;
  updateBrightness ();
  
  // turn on the onboard led for testing brightness
  analogWrite(/* esp12f onboard led */ 2, 255);

  // setup pins with a test pwm
  analogWrite(PIN_5, red);
  analogWrite(PIN_6, green);
  analogWrite(PIN_7, blue);
}

void loop(void){
  // keep track of where we are in the animation
  uint8_t frame = 0;
  uint8_t frameCount = 0;
  #define KEY_FRAMES 10
  #define MS_IN_ANIMATION_DELAY 250
  #define TEMPORAL_LENGTH (MS_IN_ANIMATION_DELAY / KEY_FRAMES)
  uint8_t redSubFrames[KEY_FRAMES];
  uint8_t greenSubFrames[KEY_FRAMES];
  uint8_t blueSubFrames[KEY_FRAMES];
  // keep track of where we are in the subframe
  uint8_t subframe = KEY_FRAMES;
  /*  because subframes occur every quarter second and animation delays can be long (up to 64 seconds)
   *  we need to guess what the next color should be for the next second based on where we are now
   */
  uint8_t animationDelayCounter = 0;
  uint16_t totalSubframes = 0;

  uint8_t frameAnimationDelay = 0;
  uint8_t frameStartRed = 0;
  uint8_t frameStartGreen = 0;
  uint8_t frameStartBlue = 0;
  uint8_t frameEndRed = 0;
  uint8_t frameEndGreen = 0;
  uint8_t frameEndBlue = 0;

  // tracking temporal length so that we do not run too fast or slow based on CPU frequency
  uint8_t delayCount = 0;

  while(true) {
    // listen for HTTP requests from clients
    server.handleClient();
    // check if we are supposed to animate
    if(0 == animate) break;
    /*  we will transition several times a second (technically serveral times per animation delay)
     *
     *  [?] this delay is not really necesarry, we just need a way to not run too fast
     *
     *  [!] this delay also reduces power consumption of the esp8266 significantly
     *      not something we want necessarily, but worth mentioning in case one questions
     *      what the heck is happening
     */
    delay(1);

    if(delayCount++ < TEMPORAL_LENGTH) break;
    // do we have any subframes to animate?
    if(0 == subframe) {
      // reset the subframe counter
      subframe = KEY_FRAMES;
      // are we done with this frame?
      if(0 == animationDelayCounter) {
        // move to the next frame
        if(0 == frame) frame = (ANIMATE_BUFFER_LEN - 1) / 8;
        frame--;
        // get the next animation delay
        frameAnimationDelay = animationDelayCounter = 
        // is this a stop frame
        if(0xff == frameAnimationDelay) { animate = 0; break; }
        // is this a loop frame
        if(0x00 == frameAnimationDelay) { frame = 0; continue; }
        // set our start and end frame colors
        frameStartRed = 0;
        frameStartGreen = 0;
        frameStartBlue = 0;
        frameEndRed = 0;
        frameEndGreen = 0;
        frameEndBlue = 0;
      }
      // using the start, stop, and animation delay counter, compute subframes
      // track progress through animation delay
      animationDelayCounter--;
    }
    // set color
    setColor(redSubFrames[subframe -1], greeenSubFrames[subframe -1], blueSubFrames[subframe -1])
    // track progress through subframes
    subframe--;
  }
}

void handleRoot() {                          // When URI / is requested, send a web page with a button to toggle the LED
  //server.send(200, "text/html", "<form action=\"/login\" method=\"POST\"><input type=\"text\" name=\"username\" placeholder=\"Username\"></br><input type=\"password\" name=\"password\" placeholder=\"Password\"></br><input type=\"submit\" value=\"Login\"></form><p>Try 'John Doe' and 'password123' ...</p>");
  server.send(200, "text/html", "rain-gutter-rgb http-post (hex values): /rgb  color=\'RRGGBB\'");
}

void handleEchoHex() {
  // make sure null terminated, then send as string
  hexStr[6] = '\0';
  server.send(200, "text/html", (char*) hexStr);
}

void handleAnimate() {
  // turn on animate
  animate = 1;
}

void handleGetDec() {
  String hex =  String("");
  server.send(200, "text/html", hex + red + "," + green + "," + blue + '\n');
}

void handleGetBrightness() {
  String info = "";
  server.send(200, "text/html", info + brightness + '\n');
  return;
}

/*  we are going to cheat the brightness by adjusting pwm resolution
 *   
 *  in effect this will change the brightness and we will not need to perform any math
 *  the way this works is that PWM resolution is 10-bit but when we set the duty-cycle
 *  we only use values [0..255].  By increasing the resoltion past 255 we reduce the
 *  brightness.  Cool.
 *
 *  [?] because our gate drive voltage source is a weak reverse biased zener
 *      regulator and we just use resistors to turn off the power mosfets we
 *      have a hard time with power losses turning on and off the mosfet.  When
 *      we drive all three mosfets on with 100% duty cycle the voltage source
 *      drops well below the needed drive voltage and the mosfet Rds becomes
 *      pretty terrible.  It works but is really bad.  If we run less than
 *      50% duty we should be okay.  Using 1023 as the starting point means that
 *      at 0 brightness mosfets are driven at 25% duty (255/1032).  At 100
 *      brightness they are driven at 60% duty 255/432.
 */
void updateBrightness () {
    // default range is 0..255
    analogWriteRange(1023);
    // brightness is inverted, technically it is darkness
    uint8_t brightnessValue = 6 * (100 - brightness);
    // reducing PWM range will increase brightness
    analogWriteRange(1023 - brightnessValue);
}

void handleBrightness() {
    char buffer[4];  
    if( ! server.hasArg("brightness")) {
        server.send(400, "text/plain", "400: Invalid Request");         // The request is invalid, so send HTTP status 400
        return;
    }
    // else
    server.arg("brightness").getBytes(buffer, 3);
    brightness = (nibbler(buffer[0]) << 4) + nibbler(buffer[1]);
    // limit brightness to 100
    brightness = 100 < brightness ? 100 : brightness;
    updateBrightness();
    handleGetBrightness();
    return;
}

void handleCfg() {
  uint8_t valid = 0;
  char buf[3];
  if(server.hasArg("quickGamma")) {
    server.arg("quickGamma").getBytes(buf, 2);
    gammaCorrectionType = '1' == buf[0]
        ? USE_BG100_S_CURVE_GAMMA_CORRECTION
        : DISABLE_GAMMA_CORRECTION;
    valid += 1;
  }
  if(server.hasArg("sCurveGamma")) {
    server.arg("sCurveGamma").getBytes(buf, 2);
    gammaCorrectionType = '1' == buf[0]
        ? USE_PHILIP_GAMMA_CORRECTION
        : DISABLE_GAMMA_CORRECTION;
    valid += 1;
  }
  if(server.hasArg("colorCorrection")) {
    server.arg("colorCorrection").getBytes(buf, 2);
    gammaCorrectionType = '1' == buf[0]
        ? ENABLE_FASTLED_CORRECTION
        : DISABLE_FASTLED_CORRECTION;
    valid += 1;
  }
  if(valid) handleGetCfg(); else server.send(400, "text/plain", "400: Invalid Request");
  return;
}

void handleGetCfg() {
  String info = "cfg [quickGamma:";
  uint8_t fastled = ENABLE_FASTLED_CORRECTION == useFastLedCorrection;
  uint8_t sCurve = USE_PHILIP_GAMMA_CORRECTION == gammaCorrectionType;
  uint8_t quick = USE_BG100_S_CURVE_GAMMA_CORRECTION == gammaCorrectionType;
  if(valid) server.send(200, "text/html", info + quick + " sCurveGamma:" + sCurve + " colorCorrection:" + fastled + ']' + '\n');
  return;
}

void handleRGB() {                         // If a POST request is made to URI /login
  if( ! server.hasArg("color")) {
    server.send(400, "text/plain", "400: Invalid Request");         // The request is invalid, so send HTTP status 400
    return;
  }
  // turn of animate
  animate = 1;
  // kinda lame but parsing is not super easy here
  server.arg("color").getBytes(hexStr, 7);
  setColor(
    /* red */ (nibbler(hexStr[0]) << 4) + nibbler(hexStr[1]),
    /* green */ (nibbler(hexStr[2]) << 4) + nibbler(hexStr[3]),
    /* blue  */ (nibbler(hexStr[4]) << 4) + nibbler(hexStr[5])
  )
  String info = "degub r:";
  server.send(200, "text/html", info + red + " g:" + green + " b:" + blue + '\n');
}

void setColor(uint8_t r, uint8_t g, uint8_t b) {
  // store colors for API
  red   = r;
  green = g;
  blue  = b;
  /*  [!] it looks like we always correct color, this is not the case
   *  the correctColor() routine, and the chained gammaCorrection() routine
   *  check configuration settings before setting the LED color.
   *  
   *  the fast-led correction tones down green significantly and blue a bit.
   *  Both linearly, I assume this is not to adjust for human eye sensitivity
   *  but just for the junction efficiency
   */
  analogWrite(PIN_5, correctColor(red,   FASTLED_RED_CORRECTION));
  analogWrite(PIN_6, correctColor(green, FASTLED_GREEN_CORRECTION));
  analogWrite(PIN_7, correctColor(blue,  FASTLED_BLUE_CORRECTION));
}
// converts ASCII utf8 chars to integer values, [0..F], otherwise zero
uint8_t nibbler(uint8_t v) {
  switch (v) {
    case 'f': case 'F': return 15;
    case 'e': case 'E': return 14;
    case 'd': case 'D': return 13;
    case 'c': case 'C': return 12;
    case 'b': case 'B': return 11;
    case 'a': case 'A': return 10;
    case '9':           return 9;
    case '8':           return 8;
    case '7':           return 7;
    case '6':           return 6;
    case '5':           return 5;
    case '4':           return 4;
    case '3':           return 3;
    case '2':           return 2;
    case '1':           return 1;
    default:            return 0;
  }
}

uint8_t hexStrToInt(char buf[]) {
  return (int) strtol(buf, 0, 16);
}

void handleLogin() {                         // If a POST request is made to URI /login
  if( ! server.hasArg("username") || ! server.hasArg("password") 
      || server.arg("username") == NULL || server.arg("password") == NULL) { // If the POST request doesn't have username and password data
    server.send(400, "text/plain", "400: Invalid Request");         // The request is invalid, so send HTTP status 400
    return;
  }
  if(server.arg("username") == "John Doe" && server.arg("password") == "password123") { // If both the username and the password are correct
    server.send(200, "text/html", "<h1>Welcome, " + server.arg("username") + "!</h1><p>Login successful</p>");
  } else {                                                                              // Username and password don't match
    server.send(401, "text/plain", "401: Unauthorized");
  }
}

void handleNotFound(){
  server.send(404, "text/plain", "404: Not found"); // Send HTTP status 404 (Not Found) when there's no handler for the URI in the request
}