Bluetooth Android Controlled MBED

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Remote control MBED applications using Bluetooth as wireless protocol¶

There have been several blogs on how to communicate with MBED using a Bluetooth module (HC-05 ) module. I will try to bring all the information on one page from android application development to firmware on MBED. Hope this helps :)

Ingredients of the experiment¶

1. Bluetooth HC-05 ( pin description of the same can be referred to https://mbed.org/users/edodm85/notebook/HC-05-bluetooth/
2. Android Phone
3. Installation of Android development environment using MIT App inventor http://appinventor.mit.edu/explore/get-started.html

Connecting HC05 with MBED¶

Pin- HC05	Pin-MBED
1-Tx	P10 - Rx
2 - Rx	P9 - Tx
12 - 3.3V	Vout - 3.3V
13 - GND	GND
31 - PIO8	--
32 - PIO9	- -
34 - PIO11	GND or 3.3V

Hardware¶

Building Android App¶

Main Screen¶

There are 4 buttons which are by default assigned values as follows .

Button	Assigned Value
Button#1	49
Button#2	50
Button#3	51
Button#4	52

The assigned value is sent once and is seen in "send" box ! The values assigned to button#x can be modified by updating the text box at the bottom of the application .

/media/uploads/prabhuvd/application_snapshot.jpg

Button Logic¶

/media/uploads/prabhuvd/button_logic.png Finally the button logic logic is same for all the four buttons , the data is read from the text box and sent over bluetooth , the data is entered in italic .csv format bold 11,22,33 or simply bold 11 for a single byte .

The text box is updated !! Followed , by the send operation , one byte of data (length byte) is read and indicates the total byte that will be sent by MBED . Once the length byte is received , the bluetooth module reads so many bytes of information.

Length	Byte 1	Byte 2	Byte 3	Byte 4	.....
n	11	22	33	44	..n bytes

Check out the video¶

Firmware for MBED¶

include the mbed library with this snippet

#include "mbed.h"

Serial device(p9, p10);
 
DigitalOut led1(LED1);
DigitalOut led2(LED2);
DigitalOut led3(LED3);
DigitalOut led4(LED4);
 

void send_bytes(uint8_t len ,uint8_t data)
{
    device.putc(len);
    while(len>0) {
        device.putc(data);
        len--;
    }
}

int main()
{
    unsigned char rx;
    device.baud(9600);
    while(1) {

        if(device.readable()) {
            rx =device.getc();
            pc.printf("\n Received %x \nSending : %x",rx,rx);
            switch (rx) {
                case 49:
                    /* Turn on LED#1 on receiving 49 */
                    led1 = !led1;
                    send_bytes(1,rx);
                    break;
                case 50:
                   /* Turn on LED#2 on receiving 50 and send 2 bytes of acknowledgment */
                    send_bytes(2,rx);
                    led2 = !led2;
                    break;
                case 51:
                   /* Turn on LED#3  on receiving 51 and send 3 bytes of acknowledgment */
                    led3 = !led3;
                    send_bytes(3,rx);
                    break;
                case 52:
                     /* Turn on LED#4  on receiving 53 and send 4 bytes of acknowledgment */
                    led4 = !led4;
                    send_bytes(4,rx);
                    break;
            }

        }
    }
}

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