Project 2: Arduino, DHT11, DC motor and LCD display

Description:

• Read humidity and temperature data from DHT11 sensor
• Display humidity and temperature data on LCD module
• Turn on the fan (DC motor) when the temperature reaches 25C
• Increase the fan speed as the temperature increases up to 40C.

Components Used:

• Arduino UNO R3 - micro-controller
• DHT11 sensor - gathers humidity and temperature data
• 3V-6V motor - spins the fan
• LCD 1602 module - displays the sensor data
• 9V battery - power source for the DC motor
• PN2222 transistor - to turn on and off DC motor
• 1kOhm resistor - prevent large current from flowing into the transistor base
• 5kOhm resistor - pullup resistor for DHT11
• 10uF capacitor - smooths out the noise from the DC motor
• 1N4007 diode - prevent inductive spike from the DC motor
• 10kOhm potentiometer - control the contrast of the LCD module
• Jumper cables

Fan off below 25C

Fan on above 25C (high RH from breathing on the sensor)

Notes:

• 5kOhm pull up resistor on DHT11 Vcc pin and data pin
• RW pin on LCD module to write only by connecting to ground
• Connect the grounds of the 9V battery and Arduino, but do not connect the power source.
• Electrical noise from the motor could corrupt data writing to LCD module. Solution: wrap wires around the motor to shorten the wires. This reduces noise. Adding a capacitor also helps too.
• Inductive spike from the DC motor could kill transistor without a path to direct inductive energy.
• Schottky diode for higher frequency

Code:
https://gitlab.com/hopop55/Project2_Arduino_DHT11_DCmotor_LCDdisplay/blob/master/humidity_lcd2.ino

Resources:

• DHT11 datasheet
  http://www.micro4you.com/files/sensor/DHT11.pdf

• LCD module pinout
  https://circuitdigest.com/article/16x2-lcd-display-module-pinout-datasheet/

• Motors and transistors tutorial
  

Inductive spike from the DC motor

How to deal with electrical noise from the DC motor
https://www.pololu.com/docs/0J15/9