• July 15, 2024

Trinket Pro Humidity and Temperature Sensor for Your Desk

So, I wanted to measure the temperature and humidity in my office.  Typically, a simple hygrometer and thermometer could work.  But, how do you log the information?  Paper and pencil?  What happens when I am away?  So, in this project we wire up a small micro-controller, temperature and humidity sensor, screen, and a micro-SD card adapter to log the data. Then we use the 3D printer to make a nice little frame.

Adafruit Pro Trinket – 5V
10k Ohm Resistors (3)
DHT11 basic temperature-humidity sensor
Small Prototype Boards
SainSmart IIC/I2C/TWI Serial 2004 20×4 LCD Module Shield For Arduino UNO MEGA R3
MicroSD card breakout board+
A small SD card
Jumper Wires
Old USB phone charger

Step 1: Solder on the header pins to the trinket micro controller and SD card breakout board

Adafruit Pro Trinket 5V Chip new and pinsheader pins in prototyping boardadafruit 5V microSD breakout board about to have pins soldered onSolder chip to pins
New Trinket Pro Chip
Pin Header
Set on Chip
Solder in Pins

Step 2: Press the trinket, card board, and DHT into the prototyping board

Trinket Pro on prototyping board - onlySD board, DHT, Trinket Pro on prototyping board - no wires yet
Pro Trinket
SD Board, DHT, Trinket

Step 3: Connections:
— Trinket Pin 10 to SD Card “CS”
— Trinket Pin 11 to SD Card “DI”
— Trinket Pin 12 to SD Card “DO”
— Trinket Pin 13 to SD Card “CLK”
— Trinket Pin “5V” to SD Card “5V”
— Trinket Pin “G” to SD Card “GND”
— Trinket Pin “5V to DHT Pin 1 (looking at it from the front Left pin is 1)
— Trinket Pin “GND” to DHT Pin 4
— Trinket Pin 8 to DHT Pin 2
— 10kΩ Resistor from Trinket “5V” to Trinket Pin 8 (this is a 5V digital pull-up)
— 10kΩ Resistor from Trinket Pin A4  (this is a I2C 5V pull-up, hidden under chip in photo)
— 10kΩ Resistor from Trinket Pin A5 (this is a I2C 5V pull-up, hidden under chip in photo)
— Cable from Trinket Pin A4 to Screen Pin “SDA”
— Cable from Trinket Pin A5 to Screen Pin “SCL”
— Cable from Trinket Pin “BUS” to Screen Pin “VCC”
— Calbe from Trinket Pin “G” to Screen Pin “GND”

Trinket Pro, DHT, SD Card Board - Wired up on Prototyping Board


Step 4: Write the software
The software needs to do 3 things:
a) collect temperature and humidity from DHT
b) Format and display the info on the screen
c) Save a copy to the SD card

Software Structure:

// Libs for the Screen (Need wire for I2C and Liquid Crystal to setup Display
#include <Wire.h>
#include <LiquidCrystal_I2C.h>
// Libs for Sensor (Provides sensor functions)
#include "DHT.h"

// Libs for SD card
#include <SPI.h>
#include <SD.h>

// Constants for Sensor
#define DHTPIN 8 // What digital pin we're connected to?
#define DHTTYPE DHT11 // Sensor Type

// Constants for SD Card
const int chipSelect = 10;

// Setup DHT sensor's connection pin and type

// Setup Screen Settings
// Set the LCD I2C address to 0x27
// It has 20 chars and 4 lines
LiquidCrystal_I2C lcd(0x27,20,4); 

void setup() { 
 lcd.init();          // Initialize the lcd
 lcd.backlight();     // turns off the backlight for effect
 lcd.print("Initializing SD card...");
 // See if the SD card is inserted and can be initialized:
 if (!SD.begin(chipSelect)) {
 lcd.print("Card failed, or not present");
 // can't do do anything with it
 lcd.print("card initialized.");  //Found the card!

dht.begin();  //Start the DHT functions

//Main program Goes HERE!
void loop() {
 // Wait a few seconds between measurements.

 // Clear the Screen
 // Get humidity from Sensor and store as variable "h"
 float h = dht.readHumidity();
 // Read temperature as Celsius (the default)
 // Store temperature in variable "t"
 float t = dht.readTemperature();
 // Read temperature as Fahrenheit (isFahrenheit = true)
 float f = dht.readTemperature(true);

 // Compute heat index in Fahrenheit (the default)
 float hif = dht.computeHeatIndex(f, h);
 // Compute heat index in Celsius (isFahreheit = false)
 float hic = dht.computeHeatIndex(t, h, false);

 // Print info to the screen
 lcd.setCursor(0,0);  // Top Line
 lcd.print("Humidity: ") & lcd.print(h) & lcd.print(" %");
 lcd.setCursor(0,1);  // 2nd line
 lcd.print("Temp: ") & lcd.print(t) & lcd.print(" *C ");
 lcd.setCursor(0,2);  // 3rd line 
 lcd.print("Temp: ") & lcd.print(f) & lcd.print(" *F "); 
 lcd.setCursor(0,3);  // 4th line
 lcd.print("Heat Index: ") & lcd.print(hif) & lcd.print(" *F");

 // Make a string for assembling the data to save in log file
 // This a comma separated file that will look like this:
 // H = 10 %, T = 32 *F, T = 0 *C, HI = 12 *F
 String dataString = "";
 dataString += "H = " ;
 dataString += String(h);
 dataString += " %, T = ";
 dataString += String(f);
 dataString += "*F , T = ";
 dataString += String(t);
 dataString += "*C , HI = ";
 dataString += String(hif);
 dataString += "*F";

 // Open the file. Only one file can be open at a time
 // The file is or will be called datalog.txt
 File dataFile = SD.open("datalog.txt", FILE_WRITE);
 // If the file is open, you can write to it
 // You print the assembled string (called dataString) into the file
 // println command prints the string and moved down one line in the file
 // the next reading will be printed on the next line
 // then close the file and start all over again, go back to the top of loop code 
 if (dataFile) {

Step 5: Upload the software

Step 6: 3D print the screen holder

You can get the stl file here.

3d printing of a lcd screen frame holder
3D Printing the Frame

Step 7: Insert LCD into the Frame, stick on the control board

Screen Connected to Trinket Pro For DHT Sensor Project
Screen and board inserted into the frame.
Temp-Humidity-Sensor Frame Assembled Back
Control board fits on the frame ledge.

Step 8: DONE!

Finished DHT-Trinket-LCD in Frame
Finished Temperature and Humidity Sensor Powered by a USB phone charger