How to Interfacing Sensor with LPC2148 ARM

Temp Sensor LM35 Interfacing With ARM7 tyro

Tags: ARM7 LPC2148 Tyro Board, LM35 Interfacing, Interfacing LM35 to Microcontroller, Circuit Diagram to Interface LM35 with LPC2148, C Program to read temperature using LPC2148,
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ARM7 LPC2148 Tyro Board

The ARM7 LPC2148 Tyro 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.

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

Temperature Sensor

The LM35 series are precision integrated-circuit temperature sensors, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature. The output of sensor converted to digital that easy connecting with microcontroller.

Interfacing LM35

Fig. 1 shows how to interface the LM35 to microcontroller. As you can see the third pin is connected to GND, the first pin is connected to VCC & the second pin is connected to the Microcontroller input. Just use single PIN female to female wire to connect with the leads of LM35 temperature sensor. So when the temperature is sensing, it give the sensor reading to controller.




Fig. 1 Interfacing LM35 to Microcontroller

Interfacing LM35 with LPC2148

Read the temperature in LPC2148 Tyro Board from temperature sensor LM35. The ARM7 LPC2148 Tyro board uses the ADC pin for reading temperature from temperature sensor LM35. The reading output is displayed into PC through UART1.

The 10 bit ADC used for reading the temperature from LM35. Basic clocking for the A/D converters is provided by the VPB clock. A programmable divider is included in each converter, to scale this clock to the 4.5 MHz (max) clock needed by the successive approximation process. A fully accurate conversion requires 11 of these clocks.

Pin Assignment with LPC2148




Temp Sensor

LPC2148 Lines

Temperature Sensor







Circuit Diagram to Interface LM35 with LPC2148


Source Code

The Interfacing LM35 with LPC2148 program is very simple and straight forward, that reading temperature from temperature sensor LM35 and it display into PC through serial port. The C programs are written in Keil software. Some delay is occurring when a single data is sent to PC.

C Program to read temperature using LPC2148


Title : Program to read temperature






#include <LPC214X.H>

#include <stdio.h>


#define DONE   0x80000000

#define START   0x01000000

#define PRESET 0x00230600


void main ()


   unsigned long Val;

   VPBDIV   =   0x02;         // pclk @ 30MHz

   Serial_Init ();

   PINSEL1   =   0x01 << 24; // P0.28 configure as ADC0.1

   Welcome ();


   AD0CR   =   PRESET | 0x02;

   AD0CR   |=   START;       // Start Conversion NOW


   while (1)




         Val = AD0GDR;


     }while ((Val & DONE) == 0);


     Val = ((AD0GDR >> 6) & 0x3FF);

     printf (">> Current Temperature : %4d ", Val);

     printf ("\xF8\F \r");          






void Delay ()


   unsigned int i,j;

   for (i=0;i<50;i++)

     for (j=0;j<500;j++);




void Welcome ()


   printf ("-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.


   printf (" Developed By : R&D Wing \n\r");

   printf (" © 2009 Pantech Solutions Pvt Ltd \n\r");

   printf ("--------------------------------------


   printf ("*** Temperature Sensor Interfacing with

   Tyro Kit ***\n\r");

   printf ("---------------------------------------


   printf (">> Put Jumper J in 'E' Mode to Enable

Temp Sensor Block \n\r");

   printf (">> Connect UART1 to COM Port @ 9600

   Baud Rate\n\n\r");

   printf ("**************************************


   printf ("*************************

   Result ***********************\n\r");

   printf ("**************************************





void Serial_Init ()


   PINSEL0   |= 0x00050000; // TxD1 and RxD1 @ P0.8 & P0.9

   U1LCR   =   0x83;

   U1DLL   =   195;

   U1LCR   =   0x03;






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, Temp Sens.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 microcontroller Board.

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

Testing the LM35 Based Thermometer with LPC2148

Give +3.3V power supply to LPC2148 Tyro Board; the serial cable is connected between the controller and PC. Open the Hyper Terminal screen, select which port you are using and set the default settings. Now the screen should show the current temperature readings.

Bring a Hot soldering iron tip near the LM35's pins, don't touch it keep it 1 or 2mm away. The screen should update with the rising temperature. Now finally touch the pins of LM35 with the tip of iron, the temperature should rise quickly. Keep it there until temperature rise to 80 degrees, and then remove the iron.

General Information

  • For proper working use the components of exact values as shown in Circuit file. Wherever possible use new components.
  • Solder everything in a clean way. A major problem arises due to improper soldering, solder jumps and loose joints.
  • Use the exact value crystal shown in schematic.
  • More instructions are available in following articles,
        -Interfacing UART with LPC2148 Microcontroller.
        -Interfacing ADC with LPC2148 Microcontroller.

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