2.3 " Digital thermometer

This project is a 3-digit digital thermometer easy to build for
beginner or hobbyits.PIC16F628 used to read digital value
of temperature from a DS1820 sensor.All 7-segments drived by
power logic 8-bit shift register TPIC6B595 with open collector output. For the 7-segment need 12V volt to drive because it have 3 LED per one segment.All segment no need to scan display. Source code programming with CCS C Compiler availible.


Feature :




- 2.3 " 7-segment X 3
- Power supply 9-12Vdc from adaptor
- 0.5'C accuracy (see data sheet for more accuracy)
- display temperature rank from 00.0 - 99.5 'C
- small components count.
- easy software for beginer to understand

Figure 1. schematic for this project

The TPIC6B595 is a monolithic, high-voltage, medium-current power 8-bit shift register designed for use in systems that require relatively high load power.

Figure 2. TPIC6B595 pinout



Figure 3. TPIC6B595 logic symbol

This device contains an 8-bit serial-in, parallel-out shift register that feeds an 8-bit D-type storage register. Data transfers through both the shift and storage registers on the rising edge of the shift-register clock (SRCK) and the register clock (RCK), respectively. The storage register transfers data to the output buffer when shiftregister clear (SRCLR) is high. When SRCLR is low, the input shift register is cleared. When output enable (G) is held high, all data in the output buffers is held low and all drain outputs are off. When G is held low, data from the storage register is transparent to the output buffers. When data in the output buffers is low, the DMOS- transistor outputs
are off. When data is high, the DMOS transistor outputs have sink- current capability. The serial output (SER OUT) allows for
cascading of the data from the shift register to additional devices. From figure ,TPIC6B595 use 5 pins from PIC16F628 to control only.

#define EXP_OUT_LATCH PIN_B0 // Output latch
#define EXP_OUT_CLOCK PIN_B3 // Clock
#define EXP_OUT_DO PIN_B5 // Data
#define EXP_OUT_CLEAR PIN_B4 // output clear

Code to send data 1 byte to output of TPIC6B595

//=================================
// WRITE DATA TO 6b595
//=================================
void write_expanded_outputs(BYTE *D)
{
  BYTE i;
  for(i=1;i<=8;++i)
  {  // Clock out bits from the *D array
    if ((D & 0x80)==0)
      output_low(EXP_OUT_DO);
    else
      output_high(EXP_OUT_DO);

   D=D<<1;
   output_high(EXP_OUT_CLOCK);
   output_low(EXP_OUT_CLOCK);
  }
}      

The main loop use while statement to looping to read data from sensor then send it to TPIC6B595 and delay about 0.5 second for each loop.

void main()
{
     while(1)
     {
       1. read sensor
       2. write data (refreash display)
       3. delay 500 mS
     }
}      
      

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Download source code