Arduino Bluetooth Example

Prepared by Dr. Aaron Scher
[email protected]
Oregon Institute of Technology

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This example shows how to achieve two-way communication between a laptop running Windows 8 and an Arduino via Bluetooth. The Arduino is connected to a Bluetooth module, an LED, and a DHT22 sensor. The Arduino is used to monitor temperature and humidity via the DHT22 sensor, and this data is displayed on the laptop. A user will also be able to remotely turn on and off the LED from the laptop.

Note 1: This example draws heavily from Adafruits's Bluetooth Temperature and Humidity Sensor Tutorial. In case this link doesn't work, you can download the tutorial by clicking: here. A very thorough introduction to the Bluefruit EZ-link can also be downloaded by clicking: here.

Note 2: I use a laptop for this example running Windows 8.

Note 3: It is assumed that your laptop has Bluetooth capability.

Material list

1. Arduino Uno. Other Arduino models should also work for this example.
2. Bluefruit EZ-Link - Bluetooth Serial Link & Arduino Programmer.
3. DHT-22 temperature/humidity sesor. I happend to purchase mine from Adafruit . You also need a 10 kOhm resistor for the DHT-22 sensor. With my purchase, the sensor included this resistor.
4. Basic 5mm LED (e.g. something like this would work) and 220 Ohm resistor.
5. A simple, standard, solderless breadboard and some wire to make connections.

Step 1: Bluetooth Pairing

It's now time to "introduce" your Bluetooh moduled to your laptop. It is assumed that your laptop and your Bluetooth module are not paired. If you have already paired the two devices, then you can skip this step (Step 1).

Hardware setup

You do not need the Arduino for this part. You only need the Bluetooth module and laptop. Make sure your laptop has Bluetooth turned on. Turn on your Bluetooth module by applying 5V to the Vin pin of the Bluefruit EZ-link and ground to the GND pin. Once power is applied to the Bluetooth module, it will flash its indicator light, indicating that the device is "discoverable". This means other Bluetooth devices can detect, pair, or connect to it. For convenience, I am using my Arduino Uno's 5V and ground pin to supply the power to the Bluefruit module as shown in the diagram below. However, again, you do not need the Arduino at this step. You could power the Bluetooth module from an external power supply. In my case I am using my Arduino's 5V and GND pins to power the Bluefruit EZ-link as illustrated below.

Pairing

The Bluefruit EZ-link should be powered and slowly flashing a red LED. Now, you need to command Windows 8 to "show bluetooth devices". On my laptop, that means first clicking on the little arrow on the lower right of the bar at the bottom of the desktop as seen in the screenshot below:

Now I right click on the little bluetooth logo and select "Show Bluetooth Devices" as seen in the screenshot below.

This takes me to the new snazzy screen shown below. First make sure Bluetooth is on. Now wait a moment, and "magically" without doing anything, I see the Adafruit EZ-link device appear in the device list with the comforting message "Ready to pair". If you don't see the device appear, try rebooting the Bluefruit EZ-link (by momentarily disconnecting and reconnecting it from the power supply). You can also try pressing the tiny reset button on the device. Anyways, once the device is shown in the list, the next obvious thing to do is click on the button labeled "Pair".

After you press "pair", the Bluefruit EZ-link device flashes red very fast, and you can tell (via a little status bar) that the laptop is communicating and loading data from the Bluetooth device. At this point, I find it very important to wait for this pairing process to finish. When I say wait, I mean it. This means don't click on anything or minimize the screen. Just wait for the process to be done. If you don't, the pairing might not work correctly (even though it might seem like the pairing is successful, you might not be able to connect later if you mess around with this step). I've read online that if you are asked for a pairing code, the code is 1234, but I have not been asked for this code. You will know the pairing is complete when the Bluefruit EZ-link flashes again (as it did when it was first powered up) and the icon for the Adafruit EZ link says "Not connected". At first I was a bit alarmed that the device shows "Not connected", but this is totally normal. All you did thus far is pair the device. In fact, if you disconnect the Bluefruit EZ-link from the power all together, the icon for the Adafruit EZ-link will remain, i.e. the laptop remembers that is has paired with the Bluefruit EZ-link even when the Bluefruit EZ-link is not in range or turned on. We will connect to the Bluefruit EZ-link when sending serial data back and forth between the and the laptop. The laptop does not automatically maintain a connection to the bluetooth device in the background; this is in contrast to how the laptop does maintain a connection to a router via WiFi even when you're not surfing the net.

Step 2: Test it out

Echo test

Just for fun serial capture

1. Press the button labeled "Auto" on the Rigol to clear everything.
2. Press the Acquire button (which is is the group of buttons labeled "menu") on the Rigol. Set "MemDepth" to "Long Mem".
3. Set the vertical (amplitude) scale to 1V by turning the verical scale knob on the Rigol. The value of the vertical scale is listed in the very bottom left of the screen.
4. For 9600 baud rate communication, set the horizontal (time) scale to 200us by turning the horizontal scale knob on the Rigol. The value of the horizontal scale is listed near the bottom right of the screen.
5. Adjunst the trigger level so that it is a volt or so lower than the noisy signal displayed on the scope.
6. Press the button labeled "MENU" under the trigger knob on the Rigol. Change the "Sweep" parameter to "Single".

Hardware setup

Power

Serial communication between Bluetooth module and Arduino

Wirlessly programming the Arduino

LED

Temperature/humidity sensor

Software

//Example: Bluetooth temperature sensor and LED control.
// Bluetooth temperature sensor library.
#include "DHT.h"
     
// Pin for the DHT sensor
#define DHTPIN 7
#define DHTTYPE DHT22 //Define the type of DHT sensor (DHT22 or DHT11)
// Create instance for the DHT sensor
DHT dht(DHTPIN, DHTTYPE);
     
// Setup
void setup(void)
{
    dht.begin(); //Initialization step so we can sample the DHT sensor
    Serial.begin(115200); //begin serial connection between Arduino and Bluetooth module
    pinMode(12, OUTPUT); //Set digital pin 12 to be an output pin (for controlling LED)
}
     
void loop(void)
{
    // Get command
    if (Serial.available()) { //Checks to see if the number of bytes (characters available 
                              //for reading from serial port is not zero (i.e. serial data is available)
     
      // Read command
      byte c = Serial.read (); //read incoming serial data, store in a variable "c". 
     
      // If a measurement is requested, measure data and send it back
      if (c == 'm'){
     
      int h = (int)dht.readHumidity();
      int t = (int)dht.readTemperature();
     
      // Send data (temperature,humidity)
      Serial.println(String(t) + "," + String(h));
      }
      if (c == 'h') {  //If command to turn on LED is requested, turn LED on
       digitalWrite(12, HIGH);  
      }
      if (c == 'l') {  //If command to turn off LED is request, turn LED off
        digitalWrite(12, LOW);  
    }
  }
}

Application