The schematic is available in PDF format: Thermometer.pdf

Here is the code and project documentation:

//-----< THERMO.C >----------------------------------------------------

// This is a very simple application showing the use of a LM34 temp.

// sensor driving the 16C71's A/D. The simplicity of driving a multi-

// plexed display is shown. The code simply alternates between one

// digit and the next to give the illusion of a two digit display.

//

// The LM34 outputs 10 mV / Deg F, it is scaled by the OPAMP to be

// 1 LSB per Deg F (Gain = 2) at the input to the A/D. This gives

// one degree resolution. The maximum temperature readout is 99 deg

// F, which is good enough for where I live, but you may need to add

// a digit (ouch, that's hot!).

//

// The digital thermometer was built on copper clad PCB material and

// mounted to a craft store wood base. It is self powered by the use

// of a Radio Shack AC to 12 V transformer and a LM7805

// voltage regulator.

//

// The thermometer can be powered by any 5 volt source, even a wall

// wart.

//

// The code is written in CCS PIC-C (www.ccsinfo.com)

//---------------------------------------------------------------------

//

// By: S.C.Hageman - 16Jan96

//

//---------------------------------------------------------------------

//

// Version Control:

// V.0 - Release 0 - 16Jan96 - SCH

//

//-------------------------------------------------------------------

//-----< Includes >--------------------------------------------------

#include <pic16c71.h>

#include <picbasic.h>

//-----< PCM Use directives >----------------------------------------

#use delay(clock=4000000)

//-----< Port definitions >------------------------------------------

#pragma byte port_a = 5

#pragma byte port_b = 6

//-----< Pin definitions >-------------------------------------------

#pragma bit Ones_column = port_a.2

#pragma bit Tens_column = port_a.3

//-----< Program constants >-----------------------------------------

#define DOOMSDAY 0

//-----< Program global variables >----------------------------------

int Display_value;

int Counter;

//-----< Display routine >------------------------------------------

set_digit(int value)

{

// Set proper values for drivers

// A zero value on the bit turns the segment on, hence the 0xff code

// turns all segments off. Bit 7 of port B is not used.

switch(value)

{

case 0: port_b = 0x40; break;

case 1: port_b = 0x79; break;

case 2: port_b = 0x24; break;

case 3: port_b = 0x30; break;

case 4: port_b = 0x19; break;

case 5: port_b = 0x12; break;

case 6: port_b = 0x02; break;

case 7: port_b = 0x78; break;

case 8: port_b = 0x00; break;

case 9: port_b = 0x18; break;

default: port_b = 0xff;

}

}

//-----< Main Program >----------------------------------------------

main()

{

// Set up the ports, clear them

#asm

// Port B to all outputs, then all off

movlw 0x00

tris port_b

clrf port_b

 

// Port A bits 0,1 to inputs, then the rest off

movlw 0x03

tris port_a

clrf port_a

#endasm

 

// Power up delay of 1 second

delay_ms(1000);

 

// Initilize A/D

setup_port_a(RA0_RA1_ANALOG);

setup_adc(ADC_CLOCK_INTERNAL);

set_adc_channel(RA_0);

 

// Initilize global variables

Display_value = 88; // 88 acts as segment test at start

Counter = 0; // Set sample counter to zero

 

// Main display loop

while(!DOOMSDAY)

{

 

// Sample temperature every 1 second

if(Counter >= 50)

{ // If here then it must be time to sample the sensor

// The 2 below is the offset value from the LM34 I used

Display_value = read_adc() - 2;

// Reset counter

Counter = 0;

}

else

{

// Increment counter

Counter++;

}

 

// Set ones column off

ones_column = OFF;

 

// Display tens value

set_digit(Display_value / 10);

tens_column = ON;

 

// Wait for multiplex time

delay_ms(10);

 

// Set tens column off

tens_column = OFF;

 

// Display ones value

set_digit(Display_value % 10);

ones_column = ON;

 

// Wait for multiplex time

delay_ms(10);

 

} // End of main while loop

}

//-----< Fini THERMO.C >---------------------------------------------

// Man this was an easy program to code.....SCH