You already know my silicon diode thermometer,
this time I'm using a Microchip MCP9700A analog temperature sensor :
cheap and easy to use, factory calibrated, it is plug and play.

Let's plug it to an EasyPIC4 to see how we can play with it !

the sensor : Microchip MCP9700A Thermistor

The MCP9700A is a low power linear active thermistor from Microchip, it features :

• a tiny package, only 3 pins : Ground, power supply and output 
• a temperature measurement range from -40°C to +125°C with +/- 2°C accuracy
• a power supply range from 2.3V to 5.5V with a very low operating current : 6µA !
• a +10mV/°C temperature coefficient

It is designed to be directly connected to a PIC analog input :

MCP9700A circuit example (from Microchip datasheet)

Its linear output simplifies software : 500mV ouput is 0°C, and 10mV is 1°C :

MCP9700A output voltage curve (from Microchip datasheet)

Other similar sensors of the same family are MCP9700, MCP9701, MCP9701A.

To learn more about these sensors, please read the datasheet :
http://ww1.microchip.com/downloads/en/DeviceDoc/21942c.pdf

Plug and play

If you have an EasyPIC board, just put the MCP9700A sensor in place of the DS1820 sensor this way :

Take care to plug the MCP9700A correctly : the flat side of the package must be on the D1820 curved side !

Then connect JP14 to RE2. That's all !

C source code example

Here is a mikroC source code example to display temperature in Celcius and Fahrenheit degrees on a LCD, using a MCP9700A temperature sensor.
If you don't have mikroC compiler you can download it from : http://www.mikroe.com/en/compilers/mikroc/pic/

As you can see, I took advantages of the new mikroC LCD custom character generator to build symbols for °C and °F, as well as new "export code to HTML" feature of mikroC V7.0.0.3 to add color to the source code for better clarity :

/* ******************************************************************************* * PIC DIGITAL THERMOMETER USING A MICROCHIP MCP9700A ANALOG SENSOR ******************************************************************************* * * source code example for mikroC users * feel free to use this code at your own risks * * target : PIC16F877A, 8 Mhz crystal * HS clock, no watchdog. * * easyPIC4 settings : * MCP9700A on DS1820 socket, see web page for more details. * * Author : Bruno Gavand, September 2007 * see more details on http://www.micro-examples.com/ * ******************************************************************************* */ /* * LCD_printfix constants */ #define INT_RANGE 1000 // integer part : 3 digits #define DEC_RANGE 10 // decimal part : 1 digit /* * this counter is incremented on each TIMER0 overflow */ unsigned int cntr ; long temp ; // Temperature in Celcius * 10 int fahr ; // Temperature in Fahrenheit * 10 /* * offset reference of the sensor : 0°C is 500 mV => 102.4 * since the sensor is factory calibrated, there is no need for adjustment */ int ref = 1024 ; // offset is multiplied by 10 to get tenth of degrees /* * LCD character definitions, generated by mikroC LCD Custom Character tool : */ const char characterC[] = {8,20,8,0,3,4,4,3}; // °C const char characterF[] = {8,20,8,0,7,4,6,4}; // °F /* * print character pointed to by def at line pos_row column pos_char on LCD */ void CustomChar(const char *def, unsigned char n, char pos_row, char pos_char) { char i ; LCD_Cmd(64 + n * 8) ; for(i = 0 ; i<=7 ; i++) { LCD_Chr_Cp(def[i]) ; } LCD_Cmd(LCD_RETURN_HOME) ; LCD_Chr(pos_row, pos_char, n) ; } /* * print v with fixed-size integer and decimal parts */ void LCD_printFix(unsigned int v) { unsigned int w ; unsigned int d ; unsigned char n ; unsigned char blk = 1 ; // zero blanking if(v >= 0) { LCD_Chr_Cp('+') ; } else { LCD_Chr_Cp('-') ; } v = abs(v) ; w = v / DEC_RANGE ; for(d = INT_RANGE / 10 ; d > 0 ; d /= 10) { n = (w / d) % 10 ; if(n) { blk = 0 ; } if(blk) { LCD_Chr_Cp(' ') ; } else { LCD_Chr_Cp('0' + n) ; } } LCD_Chr_Cp('.') ; w = v % DEC_RANGE ; for(d = DEC_RANGE / 10 ; d > 0 ; d /= 10) { LCD_Chr_Cp('0' + (w / d) % 10) ; } } /* * interrupt routine, called on each timer0 overflow */ void interrupt(void) { if(INTCON.T0IF) // timer 0 overflow ? { cntr++ ; // increment counter INTCON.T0IF = 0 ; // done } } /* * program entry */ void main() { ADCON1 = 0x00 ; // set PORTA as analog input TRISA = 0xff ; // set PORTA as inputs TRISD = 0 ; // PORTD is output LCD_Init(&PORTD) ; // Initialize LCD connected to PORTD LCD_Cmd(Lcd_CLEAR) ; // Clear display LCD_Cmd(Lcd_CURSOR_OFF) ; // Turn cursor off LCD_Out(1, 1, "MCP9700A EXAMPLE"); // Print welcome message OPTION_REG = 0x80 ; // start timer 0, no prescaler INTCON = 0xA0 ; // allow timer 0 overflow interrupt for(;;) // forever { if(cntr >= 4000) // if enough time since last sample { /* * read the sensor */ temp = Adc_Read(7) * 10 - ref ; // read RE2 ADC, adjust to 0°C /* * get the result in celcius * 10 * sensor temperature coefficient is +10mV/°C * ADC resolution is 5000/1024 = 4.88 mV so one ADC point is 0.488°C */ temp *= 488 ; temp /= 1000 ; fahr = ((9 * temp) / 5 ) + 320 ; // convert C degrees to F * 10 /* * print temperature in °C on LCD */ LCD_Out(2, 1, "") ; LCD_printFix(temp) ; CustomChar(characterC, 0, 2, 7) ; /* * print temperature in °F on LCD */ LCD_Out(2, 10, "") ; LCD_printFix(fahr) ; CustomChar(characterF, 1, 2, 16) ; cntr = 0 ; // clear counter } } }

Is it plugged ? Then play !

It should work at first try, this is what you should get on your LCD screen :

Plug and play, as I said

This sensor can take place in applications where relative temperature changes are monitored, rather than absolute temperature : computer fan control, home appliance, motors and batteries temperature control for robotics...

Please report bugs, comments or suggestions in my forum.