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How to Interface Bluetooth with LPC2148 ARM7 Development Board

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The ARM7 LPC2148 Development Board is specifically designed to help students to master the required skills in the area of embedded systems. The kit is designed in such way that all the possible features of the microcontroller will be easily used by the students. The kit supports in system programming (ISP) which is done through serial port.

NXPโ€™s ARM7 (LPC2148), ARM Development Kit is proposed to smooth the progress of developing and debugging of various designs encompassing of High speed 32-bit Microcontrollers.

Bluetooth

Bluetooth is a proprietary open wireless technology standard for exchanging data over short distances from fixed and mobile devices, creating personal area networks (PANs) with high levels of security. Bluetooth technology allows electronic devices to communicate wirelessly.

Interfacing Bluetooth

Fig. 1 shows how to interface the Bluetooth with microcontroller. Bluetooth technology handles the wireless part of the communication channel; it transmits and receives data wirelessly between these devices. It delivers the received data and receives the data to be transmitted to and from a host system through a host controller interface (HCI). The most popular host controller interface today is either a UART or a USB. Here, I will only focus on the UART interface; it can be easily show how a Bluetooth module can be integrated on to a host system through a UART connection.

Interfacing Bluetooth to Microcontroller
Fig. 1 Interfacing Bluetooth to Microcontroller

Interfacing Bluetooth with LPC2148

We now want to transmit & receive the data from host system to LPC2148 Development Board by using Bluetooth module through UART0. The serial data is taken from or sent to the host system by using Bluetooth module through MAX232 into the SBUF register of LPC2148 microcontroller (refer serial interfacing with LPC2148). The serial data from the host device is taken by using the Serial Interrupt of the LPC2148 controller. The UART0 pin lines are used to transmit & receive operations in LPC2148 Development Board.

Pin Assignment with LPC2148

Circuit Diagram to Interface Bluetooth with LPC2148

Circuit Diagram to Interface Bluetooth with LPC2148

Source Code

The Interfacing Bluetooth module with LPC2148 program is very simple and straight forward, which send a message to mobiles from LPC2148 Development Board through Bluetooth module by using UART0. Some delay is occurring when a single data is sent to mobile through UART. C programs are written in Keil software. The baud rate of microcontroller is 9600.

C Program to transmit or receive data in LPC2148

#define CR 0x0D
#include  void init_serial (void);
int putchar (int ch);
int getchar (void);
unsigned char test;
int main(void)
{
char *Ptr = "*** UART0 Demo ***\n\n\rType Characters to be echoed!!\n\n\r";
VPBDIV = 0x02;
// Divide Pclk by two init_serial();
while(1)
{
while (*Ptr)
{
putchar(*Ptr++);
}
putchar(getchar());
// Echo terminal
}
}
void init_serial (void)
{
PINSEL0 = 0x00000005;
// Enable RxD0 and TxD0 U0LCR = 0x00000083;
//8 bits, no Parity, 1 Stop bit U0DLL = 0x000000C3;
//9600 Baud Rate @ 30MHz VPB Clock U0LCR = 0x00000003;
}
int putchar (int ch)
{
if (ch == '\n')
{
while (!(U0LSR & 0x20));
U0THR = CR;
}
while (!(U0LSR & 0x20));
return (U0THR = ch);
}
int getchar (void)
{
while (!(U0LSR & 0x01));
return (U0RBR);
}

To compile the above C code you need the KEIL software. They must be properly set up and a project with correct settings must be created in order to compile the code. To compile the above code, the C file must be added to the project.

In Keil, you want to develop or debug the project without any hardware setup. You must compile the code for generating HEX file. In debugging Mode, you want to check the port output without LPC2148 Development Board.

The Flash Magic software is used to download the hex file into your microcontroller IC LPC2148 through UART0.

Testing the Bluetooth with LPC2148

Give +3.3V power supply to LPC2148 Development Board; connect the 5V adapter with Bluetooth module which is connected with the LPC2148 Development Board. There are two Bluetooth modules are required. One is connected with LPC2148 Development Board; other one is connected with PC.

First connect the serial cable between LPC2148 Development Board & PC. Then open the Hyper Terminal screen, select which port you are using and set the default settings. Now the screen should show some text messages. If the messages are correctly displayed in Hyper Terminal, then only connect the Bluetooth modules in LPC2148 Development Board UART0 & PC.

If you are not reading any data from UART0, then you just check the jumper connections & just check the serial cable is working. Otherwise you just check the code with debugging mode in Keil. If you want to see more details about debugging just see the videos in below link.

โ˜žHow to Create and Debug a Project in Keil .

General Information

โ˜žFor proper working use the components of exact values as shown in Circuit file. Wherever possible use new components.

โ˜žSolder everything in a clean way. A major problem arises due to improper soldering, solder jumps and loose joints.

โ˜žUse the exact value crystal shown in schematic.

โ˜žMore instructions are available in following articles,

How to Interface UART with LPC2148 ARM7 Development Board

User Manual ARM7-LPC2148 Development Kit

Creating & Debugging a Project in KEIL

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