Bluetooth Technology: Wireless Communication

• Bluetooth technology is a wireless communication method for short-distance data exchange
• It is integrated into many devices, including mobile phones and computers
• The technology combines both hardware and software
• The intent is to establish personal area networks (PAN) over short distances
• Operates in the unlicensed industrial, scientific, and medical (ISM) band at 2.4 to 2.485 GHz
• Uses frequency hopping spread spectrum (FHSS) radio technology
• It is a packet-based protocol with a master-slave structure
• Bluetooth range is determined by the radio class in use
• Class 3 radios have a range of up to 1 meter or 3 feet
• Class 2 radios have a range of 10 meters or 33 feet
• Class 1 radios have a range of 100 meters or 300 feet
• Class 2 is the most used radio

Advantages

• The technology needs no cables or wires for data transfer over short distances
• Bluetooth consumes less power than other wireless communication technologies
• Bluetooth technology uses Class 2 radio and consumes only 2.5 mW of power
• Less prone to data interference
• Devices do not need a clear line of sight

Disadvantages

• Greater Radio Frequency (RF) range makes it vulnerable to interception/attack
• Intended only for short-range communications

HC-05 and HC-06 Modules

• HC-05 is a Class 2 Bluetooth module with Serial Port Profile (SPP)
• Can be configured as either master or slave
• Serves as a replacement for wired serial connections
• Has 'Command Mode' in which AT commands can be sent
• Has 'Data Mode' that transmits and receives data to another Bluetooth module

HC-05 Specifications

• Bluetooth Protocol is Bluetooth Specification v2.0 + EDR (Enhanced Data Rate)
• Frequency: 2.4 GHz ISM band
• Profiles: Bluetooth Serial Port
• Working Temperature: -20 to +75 centigrade
• Power of emitting: 3 dBm

Pins

• Vcc: Power supply for the module
• GND: Ground of the module
• TX: Transmitter the Bluetooth module
• RX: Receiver of the module
• Key: Enters AT command mode

Additional Info

• The default is DATA Mode which fits most applications
• Baud Rate: 9600 bps
• Data: 8 bits
• Stop Bits: 1 bit
• Parity/Handshake: None
• Passkey: 1234
• Device Name: HC-05

Data Mode Connection

• To Arduino:
• Vcc to 5V
• GND to G
• TX to RX
• RX to TX

Programming example

• Use Serial.begin(9600) and pinMode(13,OUTPUT) to set up the serial communication and pin 13 as an output in the void setup() function
• Inside the void loop() function, read serial data, if 'h' is received, then write the pin high using digitalWrite(13,HIGH)
• If character is 'l' then write pin 13 low using digitalWrite(13.LOW)

Configuring w/ AT Commands

• Name and password can be configured using AT commands
• Configure as either master or slave
• Set high the KEY pin of the module to enter the HC-05 into AT command mode
• Key connects either to 5V or 3.3V of Arduino
• TX of Arduino connects to TX of HC-05
• RX of HC-05 connects to RX of Arduino.

Command Mode Connections

• Tx -- Tx
• Rx ---Rx
• Vcc-- 5V
• GND -- GND
• KEY--3.3V

AT Command Mode

• Open the COM port of the Arduino connected to Bluetooth module
• Set the baud rate to 38400
• Send the command "AT" (without quotes)
• You should see "OK" returned, indicating entry into the AT command mode
• See http://www.linotux.ch/arduino/HC-0305_serial_module_AT_commamd_set_201104_revised.pdf for commands

Popular AT Commands

• AT
• AT+RESET
• AT+VERSION?
• AT+ORGL
• AT+ADDR?
• AT+ ROLE?
• AT+PSWD?
• AT+UART?
• AT+STATE?
• AT+DISC
• AT+NAME

AT Commands Defs

• AT : Check the connection
• AT+NAME : See default name
• AT+ADDR : See default address
• AT+VERSION : See version
• AT+UART : See baud rate
• AT+ROLE: See role of bt module(1=master/0=slave)
• AT+RESET : Reset and exit AT mode
• AT+ORGL : Restore factory settings
• AT+PSWD: see default password

Useful AT Commands

• To ensure the unit is responding, enter AT. The unit should respond OK
• To return the HC-05 to its default settings, enter AT+ORGL
• To see the version of your HC-05 enter AT+VERSION?
• To change the name of the device to AJCLOCK, for example, enter AT+NAME=AJCLOCK
• To change the default security code (1234) to 2332 enter AT+PSWD=2332
• To check baud rate, enter AT+UART? (my unit reset to 38400)
• To change baud rate to say, 115200, 1 stop bit, 0 parity, enter AT+UART=115200,1,0

Software Example

• Include:

#include <SoftwareSerial.h>
SoftwareSerial mySerial (10, 11); // RX | TX

• Use void setup() to set serial using Serial.begin(9600), Serial.println("Enter AT commands:") and mySerial.begin(38400) sets the HC-05 speed in AT command mode
• Inside void loop() transfer serial data

DHT11 and DHT22

Pinout

• VCC = Power supply between 3.3 and 5.5V
• Data = Digital output pin
• NC = Not in use
• GND = Ground

DHT11

• Measures and provides humidity and temperature values serially over a single wire
• Measures relative humidity from 20 to 90%, and temperature from 0 to 50°C
• It has 4 pins; one of which is used for data communication in serial form
• Uses resistive humidity and NTC temperature measurement component
• Ultra-low cost
• Operates between 3 to 5V
• Uses 2.5mA during conversion
• Good for humidity readings between 20-80% with 5% accuracy
• Good for temperature readings between 0-50°C, with ±2°C accuracy

DHT22

• Low cost
• Operates between 3 to 5V
• Uses 2.5mA during conversion
• Good for humidity readings between 0-100% with 2-5% accuracy
• Good for temperature readings between -40 to 125°C, with ±0.5°C accuracy

Setup for Arduino

• Download DHTLib

• Then go to Sketch>Include Library>Add .ZIP Library and select the DHTLib.zip file

• Check the following examples: https://github.com/adafruit/DHT-sensor-library

• Needs:

#include <Adafruit_Sensor.h>
#include "DHT.h"

• Add: #define DHTPIN 2 and #define DHTTYPE DHT11, and then initialize the DHT using: DHT dht(DHΤΡΙΝ, DHTTYPE)
• Example Arduino code:

void loop()
{
  delay(2000);
  float h = dht.readHumidity();
  float t = dht.readTemperature();
  Serial.print("Humidity: \t" );
  Serial.print(h);
  Serial.print(" % \n");
  delay(500);
  Serial.print("Temperature: \t");
  Serial.print(t);
  Serial.print(" *C \n");
}