Thermometer with OLED display

This article describes the construction of a simple thermometer with a DS18B20 sensor. We are ending a board with ESP8266-E12 and integrated OLED display and a Sensor DS18B20 without board. The circuit is very simple and the sensor can be soldered directly to the board.

Circuit:

View:

Since the ESP8266 supports WiFi, I have already built in the sketch the support of a second remote sensor. This second sensor will communicate with the thermometer with ESP-Now, a protocol with which very energy-saving solutions can be created. The measurement results are then displayed alternately on the display. If no remote sensor is connected, only the value of the internal sensor is displayed.

The sketch is commented in detail.

Sketch:

/* Esp8266 with OLED display as thermometer 
 */

Libraries for WiFi 
#include <ESP8266WiFi.H>
Library for OLED Display
#include <U8g2lib.H>
Libraries for DS18B20 Temperature Sensor
#include <OneWire.H>
#include <DallasTemperature.H>

Library for ESP-Now
External "C"{
#include <espnow.H>
}

Pins for temperature sensor
Const Byte Bus = 0;pin GPIO0

Protocol for reading out the sensor
OneWire oneWire(Bus);

Sensor instance
DallasTemperature Sensors(&oneWire);

Array to store sensor addresses
DeviceAddress Addresses;

Initialize display
U8G2_SSD1306_128X32_UNIVISION_F_SW_I2C u8g2(U8G2_R0, /* clock=*/ 5, /* data=*/ 4, /* reset=*/ 16);

Offset for calibration of temperature
Const uint8_t Offset = 15;

Values of the temperature sensors -127 = the value, 
which you get when no sensor is connected    Float Outside = -127;   Float Inside = -127;

After a reset, the SSID is visible so that a remote sensor can be 
can connect. After about 2 minutes the SSID should be hidden 
Counter for switching off the visible SSID  
Int Cnt = 24;

Logos as bitmap for display
#define haus_width 16
#define haus_height 16
Static Unsigned Char haus_bits[] = {    0x80, 0x0c, 0xc0, 0x0d, 0x60, 0x0f, 0x30, 0x0e, 0x18, 0x0c, 0xcc, 0x19,    0x46, 0x31, 0x47, 0x71, 0xc5, 0x51, 0x04, 0x10, 0xf4, 0x16, 0x94, 0x16,    0x94, 0x16, 0x94, 0x10, 0x94, 0x10, 0xff, 0xff };

#define baum_width 16
#define baum_height 16
Static Unsigned Char baum_bits[] = {    0x00, 0x00, 0x00, 0x00, 0xe0, 0x01, 0x10, 0x05, 0x08, 0x0a, 0x34, 0x13,    0x04, 0x10, 0x02, 0x10, 0x02, 0x08, 0x04, 0x16, 0x18, 0x10, 0xd0, 0x17,    0xa0, 0x09, 0x80, 0x01, 0x80, 0x01, 0xff, 0xff };


Data structure for data exchange via ESP Now
Struct DATEN_STRUKTUR {     Float Temp = 0;
};

Network Name
Char* Ssid = "Thermometer";


Callback function when data has been received 
Void on_receive_data(uint8_t *Mac, uint8_t *r_data, uint8_t Len) {       DATEN_STRUKTUR Data;     we copy the received data to the data structure     to be able to access the data structure     Memcpy(&Data, r_data, Sizeof(Data));     Outside = Data.Temp;   };
 
function to print a sensor address
Void printAddress(DeviceAddress Addresses)
{   for (uint8_t Ⅰ = 0; Ⅰ < 8; Ⅰ++)   {     If (Addresses[Ⅰ] < 16) Serial.Print("0");     Serial.Print(Addresses[Ⅰ], Hex);   }
}

Void Setup() {   Serial.Begin(115200);       Wifi.Begin();   Configuration of the access point   Wifi.Fashion(WIFI_AP);      Wifi.softAP(Ssid);    Initialize ESOP-Now     If (esp_now_init()!=0) {     Esp.restart();     Delay(1);   }       SET ESP role 1=Master, 2 = Slave 3 = Master + Slave   esp_now_set_self_role(2);    and register callback function   esp_now_register_recv_cb(on_receive_data);     Preparing the display   u8g2.Begin();   u8g2.enableUTF8Print();   u8g2.setFontMode(0);   Initialize temperature sensor   Sensors.Begin();   Serial.Print(Sensors.getDeviceCount(), DEC);   Serial.println(" Sensors found.");   Now let's check if the bus is in parasitic mode   Serial.Print("Parasitic mode is ");   If (Sensors.isParasitePowerMode()) {     Serial.println("ON");   } else {     Serial.println("OFF");   }   Now we check if one of the sensors on the bus is a temperature sensor   If (!Sensors.getAddress(Addresses,0)) {     Serial.println("No temperature sensor available!");   }   View addresses   Serial.Print("Address: ");   printAddress(Addresses);   Serial.println();   Sensors.setResolution(Addresses,12);   Serial.Print("Resolution = ");   Serial.Print(Sensors.getResolution(Addresses), DEC);   Serial.println();   Pullup resistance for temperature sensor   pinMode(0,INPUT_PULLUP);
}

Void Loop() {   Char Text[50] = {0}; Text buffer for display   Int Tmp; Temporary for temperatures   Sensors.requestTemperatures(); Sensor measurement start   Delay(800);Time to measure the temperature   Inside = Sensors.getTempC(Addresses); Reading temperature from the sensor   We convert the temperature to integer with a decimal place   Tmp = round(Inside * 10);   Generate output text   Sprintf(Text,"%2d.%0 1d°C", Tmp/10-Offset, Abs(Tmp%10));   and send to display   u8g2.firstPage(); Thu {     first the logo     u8g2.drawXBM( 0, 8, haus_width, haus_height, haus_bits);     then the text     u8g2.setFont(u8g2_font_osb26_tf);     u8g2.setFontDirection(0);     u8g2.drawUTF8(20, 30, Text);   } while ( u8g2.nextPage() );     Delay(5000); 5 seconds to wait   Reduce the counter   If (Cnt > 0) Cnt--;   Do we have a value from a remote sensor   Then we show the   If (Outside !=  -127) {     We convert the temperature to integer with a decimal place     Tmp = round(Outside * 10);     Generate output text     Sprintf(Text,"%2d.%0 1d°C", Tmp/10, Abs(Tmp%10));     and send to display     u8g2.firstPage(); Thu {       first the logo       u8g2.drawXBM( 0, 8, baum_width, baum_height, baum_bits);       then the text       u8g2.setFont(u8g2_font_osb26_tf);       u8g2.setFontDirection(0);       u8g2.drawUTF8(20, 30, Text);     } while ( u8g2.nextPage() );     Delay(5000); 5 seconds to wait     Reduce the counter     If (Cnt>0) Cnt--;   }   When counters on 0 hide the SSID   If (Cnt <= 0) Wifi.softAP(Ssid,Null,1,1);
}   

With a suitable LiPo battery with 3.7 V, the thermometer can be operated with battery. The charge controller and battery jack are available on the board.