Summary of DHT22 Low Cost Humidity Sensor using PIC18F25K20 with Proteus Simulation
This project shows interfacing a DHT22 (RHT03) temperature and humidity sensor with a PIC18F25K20 in Proteus, reading 40-bit timed data via a single-wire protocol on RA0, decoding via Timer2 pulse-width measurement, validating with checksum, and displaying results on a 16×2 LCD using XC8 firmware and the PIC internal 4 MHz oscillator.
Parts used in the DHT22 Low Cost Humidity Sensor using PIC18F25K20 with Proteus Simulation:
- PIC18F25K20 microcontroller
- DHT22 (RHT03) temperature & humidity sensor
- 16×2 character LCD (LM016L)
- 4.7kΩ pull-up resistor
- 5V power supply
- Proteus simulation environment
Introduction
This microcontroller project demonstrates how to interface a DHT22 (RHT03) digital temperature and humidity sensor with a PIC18F25K20 using Proteus simulation.
The project reads real-time temperature and relative humidity data and displays it on a 16×2 LCD.
It’s a practical example of embedded systems communication, timing-critical digital sensors, and LCD interfacing.
Designed for learners and hobbyists, this setup is ideal for understanding single-wire sensor protocols in DIY electronics.
The complete firmware is written in MPLAB XC8, making it easy to compile and modify.
How the Project Works (Overview)
The PIC18F25K20 communicates with the DHT22 sensor over a single data line connected to RA0.
The microcontroller sends a start signal, waits for the sensor response, and then reads 40 bits of data containing humidity, temperature, and checksum values.
A timer-based approach is used to measure pulse widths, which determines whether each received bit is a logical ‘0’ or ‘1’.
Valid sensor data is processed and displayed on a 16×2 LCD in human-readable form.
Block Diagram / Workflow Explanation
PIC18F25K20 initializes internal oscillator and I/O pins
Start signal sent to DHT22 via RA0
DHT22 responds with timing-encoded digital data
Timer2 measures pulse width for each bit
40-bit data frame decoded (Humidity, Temperature, Checksum)
Checksum verified to ensure data integrity
LCD displays temperature and humidity values
Key Features
Digital temperature and humidity measurement using DHT22
Single-wire sensor communication protocol
Timer-based pulse width detection
Real-time LCD data display
Checksum validation for reliable readings
Fully simulated in Proteus VSM
Uses internal oscillator (no external crystal required)
Components Used
PIC18F25K20 microcontroller
DHT22 (RHT03) temperature & humidity sensor
16×2 character LCD (LM016L)
4.7kΩ pull-up resistor
Power supply (5V)
Proteus simulation environment
Applications
Weather monitoring systems
Indoor climate monitoring
Smart home sensor nodes
Agricultural humidity tracking
Educational embedded systems labs
IoT sensor prototyping (with extensions)
Explanation of the Code (High-Level)
Initialization section configures oscillator, I/O pins, interrupts, and Timer2
Start signal function triggers communication with the DHT22
Response check routine confirms sensor presence
Byte reading function decodes each bit using pulse width timing
Interrupt service routine handles timeout conditions
Main loop continuously reads sensor data and updates the LCD
Checksum logic ensures data accuracy before display
Source Code
#include
#include
#include "lcd.h"
#define _XTAL_FREQ 4E6
#pragma config IESO = OFF, FOSC = INTIO67, FCMEN = OFF
#pragma config BOREN = OFF, PWRT = OFF
#pragma config WDTEN = OFF
#pragma config CCP2MX = PORTC, PBADEN = OFF, MCLRE = ON
#pragma config DEBUG = OFF, STVREN = ON, XINST = OFF, LVP = OFF Proteus Simulation
In Proteus VSM, the PIC18F25K20 executes the XC8 firmware while the DHT22 model generates digital pulse sequences.
The logic analyzer confirms correct timing behavior, and the LCD updates in real time with temperature and humidity values.
This allows complete verification without physical hardware.
(FAQs)
Conclusion
This project is a clean, real-world example of sensor interfacing, timing-critical communication, and LCD control using a PIC microcontroller.
It’s perfect for anyone learning embedded systems through Proteus simulation and practical electronics.
By studying and modifying this design, you gain hands-on experience with firmware timing, digital sensors, and reliable data handling.
- Why does the DHT22 need precise timing?
Because data bits are encoded using pulse width, accurate timers are essential. - Can this project run on other PIC18 devices?
Yes, with minor pin and configuration changes. - Why is Timer2 used instead of delays?
Timer-based measurement ensures accurate bit detection. - What causes checksum errors in Proteus?
Incorrect timing, missing pull-up resistor, or wrong clock frequency. - Can I replace DHT22 with DHT11?
Yes, but data format and resolution will differ. - Is external crystal required?
No, the internal 4 MHz oscillator is sufficient. - Can this project be extended for IoT?
Yes, by adding UART, Wi-Fi, or GSM modules. - Where is the sensor data displayed?
On a 16×2 LCD in human-readable form.
