ARM LPC2138/48 Mini Development Board – Temperature Sensor Interfacing(ADC)
LPC 2138/48 has two 10-bit successive approximation ADC s. ADC0 has 6 channels & ADC1 has 8 channels. The maximum possible input to ADC is 3.3V which gives output reading as 1023(The maximum value that can be represented in 10 bits). Thus the resolution is 3.3V/1023=3.22 mV.The development board has the temperature sensor MCP 9700 connected to pin P0.28 i.e, AD0.1 via jumper J11. The MCP9700/9700A and MCP9701/9701A family of Linear Active Thermistor™ Intergrated Circuit (IC) is an analog temperature sensor that converts temperature to analog voltage. It has an accuracy of ±2°C from 0°C to +70°C (MCP9700A/9701A) ±4°C from 0°C to +70°C (MCP9700/9701) while consuming 6 µA (typical) of operating current. Sensitivity is 10mV/°C. At 0°C, the output is 500mV.
Sample code to check the temperature sensor is given below. The output is displayed on LCD.
Schematic
Note: To use temperature sensor, don’t forget to short jumper J11. Leaving it open frees P0.28 and can be used for any other desired purpose.
Sample Code
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/******************************************************************************** HEADER FILE *********************************************************************************/ #include<lpc213x.h> #define RS 0x00020000 /* RS - P1.17 */ #define RW 0X00040000 /* R/W - P1.18 */ #define EN 0X00080000 /* E - P1.19 */ #define CLR 0X00FE0000 unsigned int adc_value=0; /******************************************************************************** * Function : Delay * * * * Description : Function for Delay * * * * Parameters : x - Delay time * *********************************************************************************/ int Delay(unsigned int x) { x = x*12000; while(x!=0) { x--; } return 0; } /******************************************************************************** * Function : LCD_Command * * * * Description : Function to give command to LCD * * * * Parameters : command - command to be given * *********************************************************************************/ void LCD_Command(char command) { int Temp; IO1CLR = CLR; /* Clearing the port pins */ IO1SET = EN; /* Enable pin high */ IO1CLR = RS; /* RS=0 for command register */ IO1CLR = RW; /* R/W=0 for write */ Temp = (command & 0xF0) << 16; /* Taking the first nibble of command */ IO1SET = IO1SET | Temp; /* Writing it to data line */ Delay(2); IO1CLR = EN; /* Enable pin low to give H-L pulse */ } /******************************************************************************** * Function : LCD_Command1 * * * * Description : Function to give command to LCD * * * * Parameters : command1 - command to be given * *********************************************************************************/ void LCD_Command1(char command1) { int Temp; IO1CLR = CLR; /* Clearing the port pins */ IO1SET = EN; /* Enable pin high */ IO1CLR = RS; /* RS=0 for command register */ IO1CLR = RW; /* R/W=0 for write */ Temp = (command1 & 0xF0) << 16; /* Taking the first nibble of command */ IO1SET = IO1SET | Temp; /* Writing it to data line */ Delay(2); IO1CLR = EN; /* Enable pin low to give H-L pulse */ IO1CLR = CLR; /* Clearing the port pins */ IO1SET = EN; /* Enable pin high */ IO1CLR = RS; /* RS=0 for command register */ IO1CLR = RW; /* R/W=0 for write */ Temp = (command1 & 0x0F) << 20; /* Taking the second nibble of command */ IO1SET = IO1SET | Temp; /* Writing it to data line */ Delay(2); IO1CLR = EN; /* Enable pin low to give H-L pulse */ } /******************************************************************************** * Function : LCD_Data * * * * Description : Function to display single character on LCD * * * * Parameters : data - character to be displayed * *********************************************************************************/ void LCD_Data(char data) { int Temp; IO1CLR = CLR; /* Clearing the port pins */ IO1SET = EN; /* Enable pin high */ IO1SET = RS; /* RS=1 for data register */ IO1CLR = RW; /* R/W=0 for write */ Temp = (data & 0xF0) << 16; /* Taking the first nibble of command */ IO1SET = IO1SET | Temp; /* Writing it to data line */ Delay(2); IO1CLR = EN; /* Enable pin low to give H-L pulse */ IO1CLR = CLR; /* Clearing the port pins */ IO1SET = EN; /* Enable pin high */ IO1SET = RS; /* RS=1 for data register */ IO1CLR = RW; /* R/W=0 for write */ Temp = (data & 0x0F)<<20; /* Taking the second nibble of command */ IO1SET = IO1SET | Temp; /* Writing it to data line */ Delay(2); IO1CLR = EN; /* Enable pin low to give H-L pulse */ } /******************************************************************************** * Function : LCD_String * * * * Description : Function to display string on LCD * * * * Parameters : String to be displayed * *********************************************************************************/ void LCD_String(unsigned char *dat) { while(*dat!='\0') /* Check for termination character */ { LCD_Data(*dat); /* Display the character on LCD */ dat++; /* Increment the pointer */ } } /******************************************************************************** * Function : LCD_Init * * * * Description : Function to initialize LCD * * * * Parameters : None * *********************************************************************************/ void LCD_Init(void) { Delay(15); LCD_Command(0x30); Delay(10); LCD_Command(0x30); Delay(5); LCD_Command(0x30); LCD_Command(0x20); LCD_Command1(0x28); LCD_Command1(0x01); /* Clear display */ LCD_Command1(0x06); /* Auto increment */ LCD_Command1(0x0C); /* Cursor off */ } /******************************************************************************** * Function : ADC_Conversion * * * * Description : Function to get ADC reading * * * * Parameters : None * *********************************************************************************/ int ADC_Conversion() { int ab; /* Variable to store ADC value */ Delay(1); AD0CR = AD0CR|0x01000000; /* Start conversion */ while((AD0DR&0x80000000)!=0x80000000); /* Wait here till conversion is over */ ab = (AD0DR&0x0000FFC0); /* Extracting the result */ ab = (ab>>6); /* Shift 6 bits right */ return ab; /* Return the result */ } /******************************************************************************** * Function : Int_ASCII * * * * Description : Function to store integer value in array * * * * Parameters : value - value to be stored * * * cnt - no: of digits * *********************************************************************************/ void Int_ASCII(int value,char cnt) { int i = 0; /* Local variables */ char array[7]; int values; values = value; for(i=1; i<=cnt; i++) /* Store the received value in array */ { array[i] = values%10; values = values/10; } for(i=cnt; i>=1; i--) /* Display it on LCD */ { LCD_Data(array[i]+'0'); } } /******************************************************************************** * Function : Sensor_Check * * * * Description : Function to take ADC reading & display it on LCD * * * * Parameters : None * *********************************************************************************/ void Sensor_Check() { AD0CR = 0x00200602; /* PDN=1,CLKDIV=6,channel=AD0.2 */ LCD_Command1(0x80); LCD_String("Sensor Checking...."); LCD_Command1(0xC0); LCD_String("Temp:"); adc_value = ADC_Conversion(); /* Get the result of conversion */ adc_value = ((adc_value*3.22)-500); adc_value = (adc_value/10); LCD_Command1(0xC4); /* 2nd row, 5th location */ Int_ASCII(adc_value,2); /* Display the result on LCD */ } /******************************************************************************** * Function : PORT_Initial * * * * Description : Function to initialize PORTs * * * * Parameters : None * *********************************************************************************/ void PORT_Initial(void) { IO1DIR = 0x00FE0000; /* LCD pins set as o/p */ PINSEL0 = 0x00000000; PINSEL1 = 0x05000000; /* ADC function for 0.28 & 0.29 */ PINSEL2 = 0x00000000; } /******************************************************************************** MAIN FUNCTION *********************************************************************************/ int main() { PORT_Initial(); /* Initialize the ports */ LCD_Init(); /* Initialize LCD */ LCD_Command1(0x80); /* 1st row, 1st location */ LCD_String("Sensor Checking."); LCD_Command1(0x01); /* Clear screen */ while(1) { Sensor_Check(); /* Take ADC reading */ } } /***************************** END OF PROGRAM *********************************/ |
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