This tutorial shows how to interface ESP8266 NodeMCU board (ESP12-E module) with LM35 analog temperature sensor and Nokia 5110 LCD display.
In this project the Nokia 5110 LCD display (84×48 pixel) is used to display environment temperature in degree Celsius and Kelvin.
To see how to interface NodeMCU board with Nokia 5110 LCD, visit this post:
Interfacing ESP8266 NodeMCU with Nokia 5110 LCD
About the LM35 sensor:
The LM35 temperature sensor is a three pin device (VCC, OUT and GND) with an output voltage linearly related to Centigrade temperature. Since the LM35 output varies with dependent to the temperature, we need an ADC (Analog-to-Digital Converter) module to measure this voltage. The NodeMCU microcontroller (ESP8266EX) has one ADC module with 10-bit resolution.
The LM35 output has linear +10mV/°C scale factor means the following:
If the output voltage = 10mV —> temperature = 1°C
If the output voltage = 100mV —> temperature = 10°C
If the output voltage = 200mV —> temperature = 20°C
If the output voltage = 370mV —> temperature = 37°C
and so on.
LM35 Futures (from datasheet):
- Calibrated Directly in ° Celsius (Centigrade)
- Linear + 10 mV/°C Scale Factor
- 0.5°C Ensured Accuracy (at +25°C)
- Rated for Full −55°C to +150°C Range
- Suitable for Remote Applications
- Low Cost Due to Wafer-Level Trimming
- Operates from 4 to 30 V
- Less than 60-μA Current Drain
- Low Self-Heating, 0.08°C in Still Air
- Nonlinearity Only ±¼°C Typical
- Low Impedance Output, 0.1 Ω for 1 mA Load
The ADC module converts analog data into digital data. The ESP8266EX MCU has a 10-bit ADC module with one analog channel. Negative and positive references of the ADC module are 0V (GND) and 1.0V respectively. That means a 0V is represented by 0 and 1.0V (or higher but we shouldn’t apply more than that) is represented by 1024.
LoLin version of the NodeMCU board analog input is A0 (or ADC0), it’s connected to the ESP8266EX microcontroller through voltage divider of 2 resistors (220k and 100k ohm) as shown in the image below (red circle).
With the built-in voltage divider, the NodeMCU analog channel supports inputs from 0 to 3.3V.
Also, using the LoLin NodeMCU we can supply the LM35 sensor with 5V that comes from pin 5V (or VUSB).
Hardware Required:
- ESP8266 NodeMCU board
- Nokia 5110 LCD module
- LM35 temperature sensor —-> datasheet
- micro USB cable (for programming and powering the circuit)
- 5V source (optional)
- Breadboard
- Jumper wires
NodeMCU with Nokia 5110 LCD and LM35 sensor circuit:
Project circuit schematic diagram is shown below.
The LM35 sensor has 3 pins (from left to right):
Pin 1 is power supply pin, connected to external 5V power source positive terminal (don’t forget to connect its negative terminal to any of the NodeMCU ground pins).
In the absence of 5V source, this pin may be connected to NodeMCU 3V3 pin (not recommended because LM35 sensor voltage range is from 4V to 36V).
Pin 2: output pin, connected to NodeMCU pin A0 (ADC0),
Pin 3: GND (ground), connected to NodeMCU GND pin.
The Nokia 5110 LCD which is shown in the circuit diagram has 8 pins (from left to right): RST (reset), CE (chip enable), DC (or D/C: data/command), Din (data in), Clk (clock), VCC (3.3V), BL (back light) and Gnd (ground).
The Nokia 5110 LCD is connected to the NodeMCU board as follows:
RST (reset) pin is connected to pin D0 (ESP8266EX GPIO16),
CE (chip enable) pin is connected to pin D1 (ESP8266EX GPIO5),
DC (data/command) pin is connected to pin D2 (ESP8266EX GPIO4),
DIN (data in) pin is connected to pin D3 (ESP8266EX GPIO0),
CLK (clock) pin is connected to pin D4 (ESP8266EX GPIO2),
VCC and BL are connected to pin 3V3,
GND is connected to pin GND.
NodeMCU with Nokia 5110 LCD and LM35 sensor code:
The following Arduino code requires 2 libraries from Adafruit Industries:
The first library is a driver for the Nokia 5110 LCD (PCD8544 controller), download link is below:
Adafruit Nokia 5110 LCD library
The 2nd library is Adafruit graphics library which can be downloaded from the following link
Adafruit graphics library —-> direct link
After the download, go to Arduino IDE —> Sketch —> Include Library —> Add .ZIP Library … and browse for the .zip file (previously downloaded).
The same thing for the other library file.
Hints:
The previous 2 libraries are included in the main code as follows:
1 2 | #include <Adafruit_GFX.h> // include Adafruit graphics library #include <Adafruit_PCD8544.h> // include Adafruit PCD8544 (Nokia 5110) library |
Reading analog voltage using ADC module gives a number between 0 and 1024 (10-bit resolution), 0V is represented by 0 and 3.3V is represented by 1024. Converting back the ADC digital value is easy, we can use the following equation:
Voltage (in milliVolts) = ADC_reading * 3300 / 1024
This voltage (in milliVolts) represents the temperature value in tenths degree Celsius (output value of “273” equals 27.3 °Celsius).
The temperature in tenths Kelvin = (tenth °Celsius) + 2732 (because: K = °C + 273.16).
To get the actual value of each quantity we’ve to divide it by 10. The line below shows an example for temperature in Kelvin:
1 | display.printf("%03u.%1u K", tKelvin / 10, tKelvin % 10); |
We get the first 3 digits by dividing the tenths value by 10, and the tenths number (number after the decimal point) of the actual temperature value is equal to the reminder of that division (tenths value % 10).
The resolution of this thermometer is about 0.3°C.
Full Arduino code:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 | /************************************************************************** * * ESP8266 NodeMCU with Nokia 5110 LCD (84x48 Pixel) and LM35 analog * temperature sensor. * This is a free software with NO WARRANTY. * http://simple-circuit.com/ * *************************************************************************/ #include <Adafruit_GFX.h> // include Adafruit graphics library #include <Adafruit_PCD8544.h> // include Adafruit PCD8544 (Nokia 5110) library // Nokia 5110 LCD module connections (CLK, DIN, D/C, CS, RST) Adafruit_PCD8544 display = Adafruit_PCD8544(D4, D3, D2, D1, D0); void setup(void) { // initialize the display display.begin(); // you can change the contrast around to adapt the display // for the best viewing! display.setContrast(50); display.clearDisplay(); // clear the screen and buffer display.setTextSize(1); display.setTextColor(BLACK, WHITE); display.setCursor(6, 0); display.print("TEMPERATURE="); display.setTextSize(2); display.display(); } int tKelvin, tCelsius, tFahrenheit; // main loop void loop() { // read analog voltage and convert it to tenths °C ( = millivolts) tCelsius = analogRead(A0) * 3300/1024; tKelvin = tCelsius + 2732; // convert tenths °C to tenths Kelvin // print temperature in degree Celsius display.setCursor(0, 13); if (tCelsius >= 1000) // if temperature >= 100.0 °C display.printf("%03u.%1u C", tCelsius / 10, tCelsius % 10); else // otherwise ( temperature < 100 °C) display.printf(" %02u.%1u C", tCelsius / 10, tCelsius % 10); // print temperature in Kelvin display.setCursor(0, 34); display.printf("%03u.%1u K", tKelvin / 10, tKelvin % 10); // print degree symbol ( ° ) display.drawCircle(66, 15, 2, BLACK); // now update the screen display.display(); delay(1000); // wait a second } // end of code. |
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