DHT11 Low Cost Humidity Sensor using PIC16F628A with Proteus Simulation

Introduction

This microcontroller project demonstrates how to interface a low-cost DHT11 temperature and humidity sensor with a PIC16F628A using a Proteus simulation environment.
The project reads digital temperature and relative humidity data and displays it on a 16×2 LCD.
It is a practical example of working with timing-sensitive digital sensors in embedded systems.
Using a simple circuit and clear firmware logic, this project is ideal for learning sensor interfacing.
It fits well into DIY electronics, educational labs, and beginner-to-intermediate PIC projects.

How the Project Works (Overview)

The PIC16F628A communicates with the DHT11 sensor over a single digital data line.
A start signal is generated by the microcontroller, after which the sensor responds with temperature and humidity data encoded as timed pulses.
Timer2 is used to measure pulse widths and determine whether each transmitted bit is a logic 0 or 1.
Once valid data is received and verified using a checksum, the temperature and humidity values are formatted and shown on the LCD.

Block Diagram / Workflow Explanation

1. PIC16F628A initializes LCD and Timer2

2. Start signal sent to DHT11 via RA0

3. DHT11 responds with synchronization pulses

4. PIC reads 5 data bytes (humidity, temperature, checksum)

5. Checksum is verified

6. Valid data displayed on 16×2 LCD

7. Process repeats every second

Key Features

• Digital temperature and humidity sensing using DHT11

• Single-wire sensor communication

• Timer-based pulse width decoding

• Checksum validation for data integrity

• Real-time LCD display output

• Fully simulated using Proteus VSM

Components Used

• PIC16F628A microcontroller

• DHT11 temperature & humidity sensor

• 16×2 LCD (LM016L)

• 4 MHz crystal oscillator

• 22 pF capacitors (oscillator)

• 4.7 kΩ pull-up resistor

• Power supply (VDD / GND)

Applications

• Room temperature and humidity monitoring

• Educational embedded systems labs

• Weather station prototypes

• Home automation sensor nodes

• Environmental monitoring projects

Explanation of Code (High-Level)

The firmware starts by configuring ports, disabling analog inputs, and initializing the LCD.
A start signal function pulls the data line low to request data from the DHT11.
The response check function ensures the sensor replies within a valid timing window.
Each byte is read by measuring how long the data line stays high using Timer2.
After reading humidity and temperature bytes, a checksum confirms data accuracy.
Finally, values are converted to ASCII and displayed on the LCD.

Source Code

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#include 
#include 
#include "lcd.h"
#define _XTAL_FREQ   4E6

#pragma config BOREN = ON, CPD = OFF, FOSC = HS, MCLRE = ON, WDTE = OFF, CP = OFF, LVP = OFF, PWRTE = OFF

#define Data      PORTAbits.RA0
#define DataDir   TRISAbits.TRISA0

char message1[] = "Temp = 00.0 C";
char message2[] = "RH   = 00.0 %";
unsigned short TOUT = 0, CheckSum, i;
unsigned short T_Byte1, T_Byte2, RH_Byte1, RH_Byte2;

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Complete Source Code

Proteus Simulation

In Proteus VSM, the PIC16F628A, DHT11 sensor, and LCD operate exactly as real hardware.
The simulation shows correct pulse timing on the data line and real-time updates on the LCD.
Timer-based decoding ensures stable readings even in a virtual environment.

Conclusion

This project is a clean and practical example of interfacing a digital sensor with a PIC microcontroller.
It combines timing control, data validation, and LCD display handling in a single embedded system.
Perfect for learning Proteus simulation, sensor protocols, and real-world firmware design using PIC16 devices.

Comlete File

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DHT11 Low Cost Humidity Sensor using PIC16F628A with Proteus Simulation