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SUNROM ELECTRONICS

K-Thermocouple Amp - MAX6675

Digital Output K-Type, Measure temperature from 0 to +1024 deg Celcus, SPI interface

Sunrom Part# 1219

Available We dispatch same day if ordered by 4PM (excluding holidays), then courier usually takes 2-5 days.
Quantity Pricing
Quantity :
Price (Discount%)
1-4 :
Rs.750/- (0%)
5-9 :
Rs.728/- (3%)
10-24 :
Rs.698/- (7%)
25-49 :
Rs.675/- (10%)
50-74 :
Rs.660/- (12%)
75-99 :
Rs.638/- (15%)
100-249 :
Rs.615/- (18%)
250-499 :
Rs.600/- (20%)
500-999 :
Rs.585/- (22%)
1000+ :
Rs.563/- (25%)

Measures temperature from 0 to +1024 deg Celcus with 0.25 deg C resolution. Output is simple serial SPI interface to be used with any microcontroller.

Thermocouples are very sensitive, requiring a good amplifier with a cold-compensation reference. This is an excellent digital-output amplifier which is very simple to use, and if your microcontroller has SPI interface  capability.

The board performs cold-junction compensation and digitizes the signal from a type-K thermocouple. The data is output in a 12-bit resolution, SPI-compatible, read-only format. This converter resolves temperatures to 0.25°C, allows readings as high as +1024°C.

Board Schematic

Features

  • Covers almost entire range from 0 to +1024 deg C in resolution of 0.25 deg C
  • Highly accurate 12-Bit results having 0.25°C Resolution
  • Direct Digital Conversion of Type –K Thermocouple Output
  • Cold-Junction Compensation
  • Simple SPI-Compatible Serial Interface
  • Open Thermocouple Detection

Applications

  • Heat Exchanges & Furnaces
  • Industrial Monitoring and Control
  • Appliances Control
  • HVAC Environment Monitoring
  • Automotive Applications like ECU, Exhaust Gas temperature measurement

Specification

Parameter

Min

Typical

Max

Unit

Operating Voltage

3

5

5.5

V DC

Current Consumption

0.7

 

10

mA

Conversion Time

 

0.17

0.22

Seconds

Resolution

 

0.25

 

Deg C

Serial Clock Frequency

 

 

4

Mhz Max

Pin Details

These pins are marked on PCB as follows

#

Symbol

Name

Details

1

GND

Ground

Power Supply Ground

2

+5V

Positive

Power Supply +5V DC regulated

3

CS

Chip Select

Active low Chip Select Input, Set CS low to enable serial interface

4

SCK

Serial Clock

Serial Clock Input

5

SO

Serial Out

Serial Data Out

6

N.C.

No connect

Not used

Connecting Thermocouple

Green connector is screw terminal for connection of thermocouple

Pin

Details

TC-

Alumel Lead of Type-K Thermocouple.

TC+

Chromel Lead of Type- K Thermocouple

Information

The board is a sophisticated thermocouple-to-digital converter with a built-in 12-bit analog-to-digital converter (ADC). The board also contains cold-junction compensation sensing and correction, a digital controller, an SPI-compatible interface, and associated control logic. The board is designed to work in conjunction with an external microcontroller (μC) or other intelligence in thermostatic, process-control, or monitoring applications.

Digitization

The ADC adds the cold-junction diode measurement with the amplified thermocouple voltage and reads out the 12-bit result onto the SO pin. A sequence of all zeros means the thermocouple reading is 0°C. A sequence of all ones means the thermocouple reading is +1023.75°C.

Serial Interface

The Typical Application Circuit shows the board interfaced with a microcontroller. In this example, the board processes the reading from the thermocouple and transmits the data through a serial interface.

Force CS low and apply a clock signal at SCK to read the results at SO. Forcing CS low immediately stops any conversion process. Initiate a new conversion process by forcing CS high.

Force CS low to output the first bit on the SO pin. A complete serial interface read requires 16 clock cycles. Read the 16 output bits on the falling edge of the clock. The first bit, D15, is a dummy sign bit and is always zero. Bits D14–D3 contain the converted temperature in the order of MSB to LSB. Bit D2 is normally low and goes high when the thermocouple input is open. D1 is low to provide a device ID for the board and bit D0 is three-state.

Serial interface protocol 

Serial interface timing

SO output

Open Thermocouple

Bit D2 is normally low and goes high if the thermocouple input is open.

Sample code for implementing in C language of any microcontroller  

#include <REGX51.H>
#include <stdio.h>

sbit CS = P2^0;
sbit SO = P2^1;
sbit SCK = P2^2;

//global error flag to tell you if a thermocouple is connected or not 
unsigned char tc_error; 

void init_serial( void )
{
	//9600 bps @ 11.059 MHz
	SCON = 0x50;          /* Setup serial port control register */
						  /* Mode 1: 8-bit uart var. baud rate */
						  /* REN: enable receiver */

	PCON &= 0x7F;         /* Clear SMOD bit in power ctrl reg */
						  /* This bit doubles the baud rate */

	TMOD &= 0xCF;          /* Setup timer/counter mode register */
						  /* Clear M1 and M0 for timer 1 */
	TMOD |= 0x20;         /* Set M1 for 8-bit autoreload timer */

	TH1 = 0xFD;           /* Set autoreload value for timer 1 */
						  /* 9600 baud with 11.0592 MHz xtal */

	TR1 = 1;              /* Start timer 1 */

	TI = 1;               /* Set TI to indicate ready to xmit */

}
// -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
// -=-=-=-=-  Delay x ms       -=-=-=-=-=-=-=
// -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
void delayms(int x)	 // delays x msec (at fosc=11.0592MHz)
{
	int j=0;
	while(x>=0)
	{
		for (j=0; j<100; j++);
		x--;
	}
}

void init_sensor()
{
	CS = 1; // disable chip select
	SO = 0;
	SCK = 0; 
}

float read_sensor()
{
   int i;
   unsigned int AdcResult, k;  // 16 bit
   
	CS=0;  	// Active chip select

	SCK = 1; 	//Cycle the clock for dummy bit 15
	SCK = 0;

   //--- read ADC result 12 bit --------
   AdcResult=0;
   for(i=11;i>=0;i--) {    	       
      SCK=1;
	  k = 0;
	  if(SO==1)
	  	k = 1 << i;
	  AdcResult|=k;
      SCK=0;			// falling clock
   }

   /* Read the TC Input inp to check for TC Errors */
    SCK = 1;
	if(SO==1)
    	tc_error = 1;
	else
		tc_error = 0;		
    SCK = 0;

   CS=1;
   
   //adjusts data to floating point format, and accounts for the decimal point
   return(float)(AdcResult/4.0); 
}

void main()
{
	init_serial();
	init_sensor();
	printf("Welcome\n");	
	while(1)
	{
	  if(tc_error)
	  	printf("Thermocouple Open");
	  else
		printf("%01.2f%cC",read_sensor(),0xB0); 
	  putchar(13);
	  delayms(1000);
	}
}

Note: Board does NOT include K type thermocouple, You can order it separately if required.

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