Mirko Pavleski
Published © GPL3+

Light Meter Project - Unihiker K10 with Arduino Libraries

Despite limited official Arduino support, the Unihiker K10's ESP32-S3 foundation allows determined makers to leverage standard Arduino lib.

BeginnerFull instructions provided2 hours120
Light Meter Project - Unihiker K10 with Arduino Libraries

Things used in this project

Hardware components

UNIHIKER K10 developement board
×1

Software apps and online services

Arduino IDE
Arduino IDE
Mind+

Hand tools and fabrication machines

Soldering iron (generic)
Soldering iron (generic)
Solder Wire, Lead Free
Solder Wire, Lead Free

Story

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Schematics

Schematic

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Code

Arduino Code

C/C++
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/*UNIHIKER K10 Light Meter
by mircemk, August 2025
*/

#include <TFT_eSPI.h>
#include <SPI.h>
#include "Adafruit_LTR329_LTR303.h"
#include "unihiker_k10.h"

#define M_SIZE 1.3333
TFT_eSPI tft = TFT_eSPI();
#define TFT_GREY 0x5AEB
#define TFT_LIGHTPINK 0xFDB8
#define TFT_GOLD 0xFEA0
#define TFT_LIGHTGREEN 0x9772
#define TFT_LIGHTSALMON 0xFD0F
#define INFO_PANEL_HEIGHT M_SIZE*30
#define FOOTER_HEIGHT M_SIZE*20  // Height for the version footer

UNIHIKER_K10 k10;
uint8_t      screen_dir=2;

// Light sensor
Adafruit_LTR303 ltr;

// Meter variables
float ltx = 0;
uint16_t osx = M_SIZE*120, osy = M_SIZE*120;
uint32_t updateTime = 0;
int old_analog = -999;

// Light sensor variables
uint16_t minLight = 0;
uint16_t maxLight = 1000;
uint32_t lastSensorRead = 0;
const uint32_t SENSOR_READ_INTERVAL = 100;

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

      k10.begin();
    k10.initScreen(screen_dir);
  
  if (!ltr.begin()) {
    Serial.println("Couldn't find LTR sensor!");
    while (1) delay(10);
  }
  
  ltr.setGain(LTR3XX_GAIN_1);
  ltr.setIntegrationTime(LTR3XX_INTEGTIME_50);
  ltr.setMeasurementRate(LTR3XX_MEASRATE_50);
  
  tft.init();
  tft.setRotation(1);
  tft.fillScreen(TFT_BLACK);
  analogMeter();
  drawInfoPanel(0);
  drawFooter();
  updateTime = millis();
}

void loop() {
  uint16_t visible_plus_ir, infrared;
  bool valid;
  
  if (millis() - lastSensorRead > SENSOR_READ_INTERVAL) {
    lastSensorRead = millis();
    
    if (ltr.newDataAvailable()) {
      valid = ltr.readBothChannels(visible_plus_ir, infrared);
      if (valid) {
        if (visible_plus_ir < minLight) minLight = visible_plus_ir;
        if (visible_plus_ir > maxLight) maxLight = visible_plus_ir;
        
        int mappedValue = map(visible_plus_ir, minLight, maxLight, 0, 100);
        mappedValue = constrain(mappedValue, 0, 100);
        
        plotNeedle(mappedValue, 10);
        drawInfoPanel(visible_plus_ir);
      }
    }
  }
}

void drawInfoPanel(uint16_t lightValue) {
  // Clear and draw panel
  tft.fillRect(0, M_SIZE*126, M_SIZE*239, INFO_PANEL_HEIGHT, TFT_YELLOW);
  tft.drawRect(0, M_SIZE*126, M_SIZE*239, INFO_PANEL_HEIGHT, TFT_BLACK);
  
  // Set larger font (Font 4)
  tft.setTextColor(TFT_BLACK, TFT_YELLOW);
  tft.setTextFont(4); // Larger font
  
  // Format and display text
  char infoText[40];
  snprintf(infoText, sizeof(infoText), "RAW:%-5d  RNG:%d-%d", 
           lightValue, minLight, maxLight);
  
  // Center the text in the panel
  int16_t textWidth = tft.textWidth(infoText, 4);
  int16_t xPos = (M_SIZE*239 - textWidth) / 2;
  tft.setCursor(xPos, M_SIZE*133);
  tft.print(infoText);
}

void drawFooter() {
  // Sky blue footer
  tft.fillRect(0, M_SIZE*126 + INFO_PANEL_HEIGHT, M_SIZE*239, FOOTER_HEIGHT, TFT_CYAN);
  
  // Centered version text
  tft.setTextColor(TFT_BLACK, TFT_CYAN);
  tft.setTextFont(2);  // Medium-sized font
  
  const char* versionText = "Light Intensity Meter V1.0 by mircemk";
  int16_t textWidth = tft.textWidth(versionText, 2);
  int16_t xPos = (M_SIZE*239 - textWidth) / 2;
  int16_t yPos = M_SIZE*126 + INFO_PANEL_HEIGHT + (FOOTER_HEIGHT/2 - 8);  // Vertically centered
  
  tft.setCursor(xPos, yPos);
  tft.print(versionText);
}



// #########################################################################
//  Draw the analogue meter on the screen
// #########################################################################
void analogMeter() {
  // Meter outline
  tft.fillRect(0, 0, M_SIZE*239, M_SIZE*126, TFT_LIGHTSALMON);
  tft.fillRect(5, 3, M_SIZE*230, M_SIZE*119, TFT_WHITE);

  tft.setTextColor(TFT_BLACK);  // Text colour

  // Draw ticks every 5 degrees from -50 to +50 degrees (100 deg. FSD swing)
  for (int i = -50; i < 51; i += 5) {
    // Long scale tick length
    int tl = 15;

    // Coodinates of tick to draw
    float sx = cos((i - 90) * 0.0174532925);
    float sy = sin((i - 90) * 0.0174532925);
    uint16_t x0 = sx * (M_SIZE*100 + tl) + M_SIZE*120;
    uint16_t y0 = sy * (M_SIZE*100 + tl) + M_SIZE*140;
    uint16_t x1 = sx * M_SIZE*100 + M_SIZE*120;
    uint16_t y1 = sy * M_SIZE*100 + M_SIZE*140;

    // Coordinates of next tick for zone fill
    float sx2 = cos((i + 5 - 90) * 0.0174532925);
    float sy2 = sin((i + 5 - 90) * 0.0174532925);
    int x2 = sx2 * (M_SIZE*100 + tl) + M_SIZE*120;
    int y2 = sy2 * (M_SIZE*100 + tl) + M_SIZE*140;
    int x3 = sx2 * M_SIZE*100 + M_SIZE*120;
    int y3 = sy2 * M_SIZE*100 + M_SIZE*140;

    // Green zone limits
    if (i >= 0 && i < 25) {
      tft.fillTriangle(x0, y0, x1, y1, x2, y2, TFT_GREEN);
      tft.fillTriangle(x1, y1, x2, y2, x3, y3, TFT_GREEN);
    }

    // Orange zone limits
    if (i >= 25 && i < 50) {
      tft.fillTriangle(x0, y0, x1, y1, x2, y2, TFT_ORANGE);
      tft.fillTriangle(x1, y1, x2, y2, x3, y3, TFT_ORANGE);
    }

    // Short scale tick length
    if (i % 25 != 0) tl = 8;

    // Recalculate coords incase tick lenght changed
    x0 = sx * (M_SIZE*100 + tl) + M_SIZE*120;
    y0 = sy * (M_SIZE*100 + tl) + M_SIZE*140;
    x1 = sx * M_SIZE*100 + M_SIZE*120;
    y1 = sy * M_SIZE*100 + M_SIZE*140;

    // Draw tick
    tft.drawLine(x0, y0, x1, y1, TFT_BLACK);

    // Check if labels should be drawn, with position tweaks
    if (i % 25 == 0) {
      // Calculate label positions
      x0 = sx * (M_SIZE*100 + tl + 10) + M_SIZE*120;
      y0 = sy * (M_SIZE*100 + tl + 10) + M_SIZE*140;
      switch (i / 25) {
        case -2: tft.drawCentreString("0", x0, y0 - 12, 2); break;
        case -1: tft.drawCentreString("25", x0, y0 - 9, 2); break;
        case 0: tft.drawCentreString("50", x0, y0 - 7, 2); break;
        case 1: tft.drawCentreString("75", x0, y0 - 9, 2); break;
        case 2: tft.drawCentreString("100", x0, y0 - 12, 2); break;
      }
    }

    // Now draw the arc of the scale
    sx = cos((i + 5 - 90) * 0.0174532925);
    sy = sin((i + 5 - 90) * 0.0174532925);
    x0 = sx * M_SIZE*100 + M_SIZE*120;
    y0 = sy * M_SIZE*100 + M_SIZE*140;
    // Draw scale arc, don't draw the last part
    if (i < 50) tft.drawLine(x0, y0, x1, y1, TFT_BLACK);
  }

  tft.drawString("Light", M_SIZE*(5 + 230 - 40), M_SIZE*(119 - 20), 2); // Units at bottom right
  tft.drawCentreString("Light", M_SIZE*120, M_SIZE*70, 4); // Comment out to avoid font 4
  tft.drawRect(5, 3, M_SIZE*230, M_SIZE*119, TFT_BLACK); // Draw bezel line

  plotNeedle(0, 0); // Put meter needle at 0
}

// #########################################################################
// Update needle position
// #########################################################################
void plotNeedle(int value, byte ms_delay) {
  tft.setTextColor(TFT_BLACK, TFT_WHITE);
  char buf[8]; dtostrf(value, 4, 0, buf);
  tft.drawRightString(buf, M_SIZE*40, M_SIZE*(119 - 20), 2);

  if (value < -10) value = -10; // Limit value to emulate needle end stops
  if (value > 110) value = 110;

  // Move the needle until new value reached
  while (!(value == old_analog)) {
    if (old_analog < value) old_analog++;
    else old_analog--;

    if (ms_delay == 0) old_analog = value; // Update immediately if delay is 0

    float sdeg = map(old_analog, -10, 110, -150, -30); // Map value to angle
    // Calcualte tip of needle coords
    float sx = cos(sdeg * 0.0174532925);
    float sy = sin(sdeg * 0.0174532925);

    // Calculate x delta of needle start (does not start at pivot point)
    float tx = tan((sdeg + 90) * 0.0174532925);

    // Erase old needle image
    tft.drawLine(M_SIZE*(120 + 20 * ltx - 1), M_SIZE*(140 - 20), osx - 1, osy, TFT_WHITE);
    tft.drawLine(M_SIZE*(120 + 20 * ltx), M_SIZE*(140 - 20), osx, osy, TFT_WHITE);
    tft.drawLine(M_SIZE*(120 + 20 * ltx + 1), M_SIZE*(140 - 20), osx + 1, osy, TFT_WHITE);

    // Re-plot text under needle
    tft.setTextColor(TFT_BLACK);
    tft.drawCentreString("Light", M_SIZE*120, M_SIZE*70, 4);

    // Store new needle end coords for next erase
    ltx = tx;
    osx = M_SIZE*(sx * 98 + 120);
    osy = M_SIZE*(sy * 98 + 140);

    // Draw the needle in the new postion
    tft.drawLine(M_SIZE*(120 + 20 * ltx - 1), M_SIZE*(140 - 20), osx - 1, osy, TFT_RED);
    tft.drawLine(M_SIZE*(120 + 20 * ltx), M_SIZE*(140 - 20), osx, osy, TFT_MAGENTA);
    tft.drawLine(M_SIZE*(120 + 20 * ltx + 1), M_SIZE*(140 - 20), osx + 1, osy, TFT_RED);

    // Slow needle down slightly as it approaches new postion
    if (abs(old_analog - value) < 10) ms_delay += ms_delay / 5;

    // Wait before next update
    delay(ms_delay);
  }
}

Credits

Mirko Pavleski
188 projects • 1451 followers

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