Published August 4, 2023 © GPL3+

UNO R4 Wifi as a digital thermometer

What can you do with 96 LEDs? Just show a three-digit number, in this case the most expensive thermometer.

BeginnerFull instructions provided1 hour1,520

Things used in this project

Hardware components

Arduino UNO R4 WiFi

Maxim Integrated DS18B20 Programmable Resolution 1-Wire Digital Thermometer

Through Hole Resistor, 4.7 kohm

Story

I was inspired by this article:

Arduino Uno R4 LED Matrix displays Number Character

Three digits on 12x8 dots

So I reduced the amount of pixels used for a single digit to the absolute minimum: 3x5 pixels plus one pixel distance to the next digit. Editing the font was not too much work. And there was even place to enter a decimal point, which makes it possible to show values from 0 to 99 with one decimal place. A good start for a thermometer, using the famous DS18B20, which works perfectly well with the R4, data pin connected to A0. So the chip plus the resistor can be mounted on a small PCB board and inserted into the power pins and A0.

all you need to check the heat

Arduino UNO R4 Wifi with sensor attached

Arduino UNO R4 Wifi showing temperature

Why is the matrix so dark?

The LEDs are driven by pin-28 to pin-38 using Charlieplexing. That means that an LED will not be lit permanently but only switched on for a fraction of a second. How strong may the current be? Well, when I switch off the complete matrix, my amp meter showed a consumption of 0.0937 Amperes for the whole UNO R4 Wifi. I had to cut a USB extension cable:

to insert a high quality meter, because meters like this

are not precise enough. This is Blink.ino for the matrix:

#include "Arduino_LED_Matrix.h"

ArduinoLEDMatrix matrix;

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

const uint32_t off[] = { 0, 0, 0};
const uint32_t on[] = { 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF};
// alle 96 LEDs an

void loop() {
  matrix.loadFrame(on);
  delay(5000);
  matrix.loadFrame(off);
  delay(5000);
}

When all LEDs are switch on, the amp Meter showed 0.0972 Amperes. If you divide the difference by 96 you get the average current for one LED: 0.036 milli Amperes. I was looking for a command like setBrightness or increaseBrightness - no luck. In bright daylight it is really hard to read the display.

/*
  Das teuerste Thermometer der Welt

  Zeichenanzeige auf Matrix:
  https://arduinogetstarted.com/tutorials/arduino-uno-r4-led-matrix-displays-number-character
*/

// Temperatursensor:
#include <DS18B20.h>

DS18B20 ds(A0);

// UNO-R4 Wifi LED Matrix:
#include "Arduino_LED_Matrix.h"
ArduinoLEDMatrix matrix;

byte fonts[][8] = {
  { 0, 7, 5, 5, 5, 7, 0, 0}, // 0
  { 0, 2, 6, 2, 2, 7, 0, 0}, // 1
  { 0, 7, 1, 7, 4, 7, 0, 0}, // 2
  { 0, 7, 1, 7, 1, 7, 0, 0}, // 3
  { 0, 5, 5, 7, 1, 1, 0, 0}, // 4
  { 0, 7, 4, 7, 1, 7, 0, 0}, // 5
  { 0, 7, 4, 7, 5, 7, 0, 0}, // 6
  { 0, 7, 1, 1, 1, 1, 0, 0}, // 7
  { 0, 7, 5, 7, 5, 7, 0, 0}, // 8
  { 0, 7, 5, 7, 1, 7, 0, 0}, // 9
};

byte empty[8][12], frame[8][12];

void setup() {
  Serial.begin(9600);
  Serial.println(__FILE__);
  delay(1500);
  matrix.begin();
  empty[6][7] = 1; // decimal dot
}

void loop() {
  int th, tz, te;
  while (ds.selectNext()) {
    byte address[8];
    ds.getAddress(address);
    float t = ds.getTempC();
    int ti = 10 * t;
    th = ti / 100;
    tz = ti % 100 / 10;
    te = ti % 10;
  }
  memcpy(frame, empty, sizeof empty);
  add_to_frame(th, -2);
  add_to_frame(tz, 2);
  add_to_frame(te, 7);
  matrix.renderBitmap(frame, 8, 12);
}

void add_to_frame(int index, int pos) {
  for (int row = 0; row < 8; row++) {
    long temp = fonts[index][row] << (7 - pos);
    for (int col = 0; col < 12; col++) {
      frame[row][col] |= (temp >> (11 - col)) & 1;
    }
  }
}

/*
  Das teuerste Thermometer der Welt

  Zeichenanzeige auf Matrix:
  https://arduinogetstarted.com/tutorials/arduino-uno-r4-led-matrix-displays-number-character
*/

// Temperatursensor:
#include <DS18B20.h>

DS18B20 ds(A0);

// UNO-R4 Wifi LED Matrix:
#include "Arduino_LED_Matrix.h"
ArduinoLEDMatrix matrix;

byte fonts[][8] = {
  { 0, 7, 5, 5, 5, 7, 0, 0}, // 0
  { 0, 2, 6, 2, 2, 7, 0, 0}, // 1
  { 0, 7, 1, 7, 4, 7, 0, 0}, // 2
  { 0, 7, 1, 7, 1, 7, 0, 0}, // 3
  { 0, 5, 5, 7, 1, 1, 0, 0}, // 4
  { 0, 7, 4, 7, 1, 7, 0, 0}, // 5
  { 0, 7, 4, 7, 5, 7, 0, 0}, // 6
  { 0, 7, 1, 1, 1, 1, 0, 0}, // 7
  { 0, 7, 5, 7, 5, 7, 0, 0}, // 8
  { 0, 7, 5, 7, 1, 7, 0, 0}, // 9
};

byte empty[8][12], frame[8][12];

void setup() {
  Serial.begin(9600);
  Serial.println(__FILE__);
  delay(1500);
  matrix.begin();
  empty[6][7] = 1; // decimal dot
}

void loop() {
  int th, tz, te;
  while (ds.selectNext()) {
    byte address[8];
    ds.getAddress(address);
    float t = ds.getTempC();
    int ti = 10 * t;
    th = ti / 100;
    tz = ti % 100 / 10;
    te = ti % 10;
  }
  memcpy(frame, empty, sizeof empty);
  add_to_frame(th, -2);
  add_to_frame(tz, 2);
  add_to_frame(te, 7);
  matrix.renderBitmap(frame, 8, 12);
}

void add_to_frame(int index, int pos) {
  for (int row = 0; row < 8; row++) {
    long temp = fonts[index][row] << (7 - pos);
    for (int col = 0; col < 12; col++) {
      frame[row][col] |= (temp >> (11 - col)) & 1;
    }
  }
}

UNO R4 Wifi as a digital thermometer

Things used in this project

Hardware components

Story

Three digits on 12x8 dots

Why is the matrix so dark?

Code

Sketch to measure and display temperature on the UNO R4 LED matrix.

Sketch to measure and display temperature on the UNO R4 LED matrix.

Credits

Klausj

Comments

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UNO R4 Wifi as a digital thermometer

UNO R4 Wifi as a digital thermometer

Things used in this project

Hardware components

Story

Three digits on 12x8 dots

Why is the matrix so dark?

Code

Sketch to measure and display temperature on the UNO R4 LED matrix.

Sketch to measure and display temperature on the UNO R4 LED matrix.

Credits

Klausj

Comments

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