Introduction: LCD Temperature Sensor With Freeze Alarm
Throughout the following steps, we'll see how to build an LCD Temperature sensor with a freeze alarm using Arduino and a few simple components. I used this source as an inspiration:
SparkFun Inventor's Kit Experiment Guide - v4.0. (n.d.). https://learn.sparkfun.com/tutorials/sparkfun-inv...kit-
experiment-guide---v40/circuit-4b-temperature-sensor.
This device allows a user to monitor the temperature in a room or garage, sounding an alarm when the temperature gets too low. This is useful in situations where you have containers with liquid that cannot freeze without bursting, giving a warning that said containers are near their limit for temperature.
Personally, I store drinks in the garage, and when we enter the coldest months of winter, I often forget to take them out of the garage. This freeze alarm on the Arduino could save me from having to clean up potentially exploding drinks! Maybe others feel the same and are ready to try this out!
The skill level of my target audience is: moderate to advanced.
Supplies
Components required:
Arduino Uno Board * 1
USB Cable * 1
16X2 LCD Screen LCD1602 Module (with pin header) *1
Potentiometer 10K * 1
DHT11 Temperature and Humidity Module * 1
Buzzer (active) * 1
Breadboard * 1
Jumper Wires
Optional Components:
9V1A Power supply * 1
9V Battery with Snap-on connector clip * 1
Tools required: None
Step 1: Schematic
Arduino:
*Arduino 9V Power via Power supply, USB or 9V Battery adapter
LCD:
Screen GND > GND Rail
Screen VCC > 5V Rail
Screen V0 > Potentiometer
Screen RS > Arduino Pin 13
Screen RW > GND Rail
Screen E > Arduino Pin 12
Screen D4 > Arduino Pin 11
Screen D5 > Arduino Pin 10
Screen D6 > Arduino Pin 9
Screen D7 > Arduino Pin 8
Screen A > 5V Rail
Screen K > GND Rail
Potentiometer:
+ > 5V Rail
- > GND Rail
D > Screen V0
Buzzer:
+ > Arduino Pin 7
- > GND Rail
DHT11 Temperature Sensor:
D > Arduino Pin 7
+ > 5V Rail
- > GND Rail
This schematic was designed with Tinkercad.
Step 2: Uploading Code to Arduino
Connect your Arduino via USB cable to your PC. The Arduino Create website (https://create.arduino.cc/) is a fast and easy way to write, test and upload code to your Arduino. To get started with Arduino Create, follow their existing tutorials to get quickly connected to your Arduino Uno. Once you have become comfortable with the Arduino Web editor, use it to upload the code below to your Arduino Uno.
It can also be found at this link: https://create.arduino.cc/editor/jcmatlon502/fe9f804d-b94c-4687-8fb4-aa6be933e6d8/preview
The following source was also used for inspiration and guidance in creating the code:
Brainy-Bits. (2020, October 29). How to use the DHT11 Temperature and Humidity Sensor with an Arduino!
Brainy. https://www.brainy-bits.com/post/how-to-use-the-d...
/*
Temperature Sensor with Freeze Alarm
The LCD will display readings from a temperature sensor in degrees Celsius and Fahrenheit.
The temperature sensor will read the temperature every 1 second
When the temperature gets to 32 degrees F or lower, sound the buzzer will sound chirp until the temperature gets back above 32 degrees
While the buzzer is chirping, the temperature will get re-measured every ~1/2 a second
This code uses the DHT11 temperature sensor and library.
*/
// include the EduIntro library
#include <EduIntro.h> // the EduIntro library conatins commands for reading values from the Temperature Sensor
DHT11 dht11(D7); // tell the Arduino what pins are connected to the Temperature Sensor 'D7'
// include the LiquidCrystal library
#include <LiquidCrystal.h> // the liquid crystal library contains commands for printing to the display
LiquidCrystal lcd(13, 12, 11, 10, 9, 8); // tell the Arduino what pins are connected to the display
int buzzer = 6; // the pin of the active buzzer is 6
int degreesC = 999; // temperature C readings are integers - setting to an extreme number to troubleshoot if its not working
int degreesF = 999; // temperature F readings are float but can also be returned as integer - setting to an extreme number to troubleshoot if its not working
void setup() {
lcd.begin(16, 2); // tell the lcd library that we are using a display that is 16 characters wide and 2 characters high
lcd.clear(); // clear the display
pinMode(buzzer,OUTPUT); // tell the arduino what pins are connected to the buzzer
}
void loop() {
dht11.update(); // Refresh the data getting pulled from the dht11 temperature sensor
degreesC = dht11.readCelsius(); // Reading the temperature in Celsius degrees and store in the C variable
degreesF = dht11.readFahrenheit(); // Reading the temperature in Fahrenheit degrees and store in the F variable
lcd.clear(); // clear the LCD
lcd.setCursor(0, 0); // set the cursor to the top left position
lcd.print("Degrees C: "); // print a label for the data
lcd.print(degreesC); // print the degrees Celsius
lcd.setCursor(0, 1); // set the cursor to the lower left position
lcd.print("Degrees F: "); // Print a label for the data
lcd.print(degreesF); // print the degrees Fahrenheit
unsigned char i; // setting a counter variable for how many times the buzzer sounds each loop
while(degreesF < 33) // if the temperature drops below 33 degrees F (32 degrees is freezing) then make the buzzer sound
{
// output buzzer sound
for(i=0;i<10;i++)
{
digitalWrite(buzzer,HIGH);
delay(20);//wait for 2ms
digitalWrite(buzzer,LOW);
delay(20);//wait for 2ms
delay(100);
}
// after buzzer sounds for ~half a second
dht11.update(); // refresh the data from the temperature sensor
degreesF = dht11.readFahrenheit();
}
delay(1000); //delay for 1 second between each reading (this makes the display less noisy)
}<br>
Step 3: Connecting the LCD Screen
Connect the LCD and potentiometer as shown in the schematic to verify that the LCD is functioning properly. You may have to turn the potentiometer to the left and the right to adjust the contrast in order to see text. If the LCD is connected and operating correctly, it should appear the same way as in the included image.
Step 4: Adding the Temperature Sensor
Connect the temperature sensor as shown in the schematic and in the included image. If everything is connected correctly, the temperature will be displayed in C and F instead of simply a zero as shown in the picture.
Step 5: Adding Extender Wires
Optionally, in order to be able to test the DHT11 Temperature sensor in locations other than the Arduino Uno, we'll add extensions to our jumper wires. The temperatures should be displayed the same way as the previous step, but now you have the option of putting the sensor in different environments away from your Arduino Uno.
Note: Although there are 5 wires used as extensions in the images, only three are required as indicated in the schematics. This is only because I want to re-use these extension wires for other future projects and keep them together. Two of the pins are not connected on either end.
Step 6: Adding the Buzzer
The last step is to add the buzzer (active) as shown in the schematic. Make sure you have the positive pin of the buzzer connected to pin 7 on the Arduino Uno, as it only works one way. You may have to put the buzzer on the breadboard diagonally to fit correctly. Once this step is done, your project is complete! Put the temperature sensor somewhere 32 degrees F or below, and watch the buzzer sound when it drops below freezing!
Step 7: Testing It Out
Congratulations, you've made it to the end! Now try putting the temperature sensor somewhere below freezing and wait for the buzzer when it drops below freezing. Check out our video demonstration included!
