Temperature sensor model

You can use DS 18B20 digital temperature sensor.

1.ds 18B20 Basic knowledge

DS 18B20 digital thermometer is a 1 line device produced by DALLAS Company, which has the characteristics of simple circuit and small volume. Therefore, it is very convenient to use it to form a temperature measuring system, and the circuit is simple, and many such digital thermometers can be hung on a communication line.

Characteristics of 1 and DS 18B20 products

(1), communication only needs one port.

(2) Each device in DS18B20 has a unique serial number.

(3) In practical application, temperature measurement can be realized without any external components.

(4) The measuring temperature range is -55℃. C to+125. Between C.

(5) The user can choose the resolution of the digital thermometer between 9 bits and 12 bits.

(6) Alarm settings for upper and lower limits of internal temperature.

2. Introduction of DS18B20 Pin

The pin arrangement of DS 18B20 in TO-92 package is shown in figure 1, and the pin function description is shown in table 1.

(Bottom view) Figure 1

Table 1 DS 18B20 Detailed pin function description

serial number

name

Pin function description

1

GND

Dwarf signal

2

Dairy Queen (Dairy Queen)

Data input/output pins. Open-drain single bus interface pin. When used in parasitic power, it can also supply power to devices.

three

VDD

Optional VDD pin. When working in parasitic power, this pin must be grounded.

3. How to use DS 18B20

Because DS 18B20 adopts 1 line bus protocol, that is, data can be transmitted in two directions on one data line, but for AT89S5 1 single chip microcomputer, the hardware does not support single bus protocol. Therefore, we must use software to simulate the protocol sequence of single bus to complete the access to DS 18B20 chip.

Because DS 18B20 reads and writes data on I/O lines, it has strict timing requirements for reading and writing data bits. DS 18B20 has strict communication protocol to ensure the correctness and integrity of data transmission. The protocol defines the timing of several signals: initialization timing, reading timing and writing timing. All time sequences take the master as the master device and the single bus device as the slave device. Each command and data transfer begins with the host actively initiating a write sequence. If the single bus device is required to send back data, after writing the command, the host needs to start the read sequence to complete the data reception. The transmission of data and commands is low priority.

Reset timing of DS 18B20

Reading Timing of DS 18B20

The reading timing of DS 18B20 is divided into two processes: reading 0 timing and reading 1 timing.

For DS 18B20, the single bus must be released within 15 seconds after being pulled from the host, so that DS 18B20 can transmit data to the single bus. DS 18B20 needs at least 60us to complete a read sequence.

Writing timing of DS 18B20

The write timing of DS 18B20 is still divided into two processes: write 0 timing and write 1 timing.

DS 18B20 has different requirements for writing 0 sequence and 1 sequence. When writing a 0 sequence, the single bus should be pulled down at least 60us to ensure that DS 18B20 can correctly sample the "0" level on the IO bus between 15us and 45us. When writing the 1 sequence, the single bus should be

4. Experimental tasks

The temperature measuring system consists of a piece of DS 18B20. The accuracy of measuring temperature reaches 0. 1 degree, and the measuring temperature ranges from -20 degrees to+100 degrees, which is displayed by an 8-bit digital tube.

5. Circuit schematic diagram

6. Hardware connection on the system board

(1). Connect P0.0-P0.7 in the "Single Chip Microcomputer System" area to the ABCDEFGH terminal in the "Dynamic Digital Display" area with an 8-core cable.

(2) Connect P2.0-P2.7 in the "Single Chip Microcomputer System" area to the S 1S2S3S4S5S6S7S8 terminal in the "Dynamic Digital Display" area with an 8-core cable.

(3) Insert the DS 18B20 chip into any socket in the "four-way single bus" area, and be careful not to connect the power supply and grounding signals reversely.

(4) Connect the DQ terminal corresponding to the "Four-way Single Bus" area to the P3.7/RD terminal in the "Single Chip Microcomputer System" area.

7.c language source program

#i includes & ltAT89X52. H & gt

#i includes & ltINTRINS.h & gt

Unsigned character code displaybit[]={0xfe, 0xfd, 0xfb, 0xf7,

0xef，0xdf，0xbf，0x7f }；

Unsigned character code displaycode[]={0x3f, 0x06, 0x5b, 0x4f,

0x66、0x6d、0x7d、0x07、

0x7f、0x6f、0x77、0x7c、

0x39，0x5e，0x79，0x7 1，0x00，0x 40 }；

Unsigned character code dotcode [32] = {0,3,6,9, 12, 16,19,22,

25,28,3 1,34,38,4 1,44,48,

50,53,56,59,63,66,69,72,

75,78,8 1,84,88,9 1,94,97};

Unsigned character display count;

Unsigned char displaybuf[8]={ 16, 16, 16, 16, 16};

Unsigned character time count;

Unsigned character readdata [8];

sbit dq=p3^7；

Bit sflag

Bit reset pulse (invalid)

{

Unsigned character I;

DQ = 0；

for(I = 255； I>0; I-);

DQ = 1；

for(I = 60； I>0; I-);

Return (dq);

for(I = 200； I>0; I-);

}

Void writecommands18b20 (unsigned character command)

{

Unsigned character I;

Unsigned character j;

for(I = 0； I<8; i++)

{

If ((command & amp0x0 1)==0)

{

DQ = 0；

for(j = 35； j & gt0; j-)；

DQ = 1；

}

other

{

DQ = 0；

for(j = 2； j & gt0; j-)；

DQ = 1；

for(j = 33； j & gt0; j-)；

}

command=_cror_(command， 1)；

}

}

Unsigned character readdatafromds18b20 (void)

{

Unsigned character I;

Unsigned character j;

Unsigned character temperature;

temp = 0；

for(I = 0； I<8; i++)

{

temp=_cror_(temp， 1)；

DQ = 0；

_ nop _()；

_ nop _()；

DQ = 1；

for(j = 10； j & gt0; j-)；

If (DQ== 1)

{

temp = temp | 0x80

}

other

{

temp = temp | 0x00

}

for(j = 200； j & gt0; j-)；

}

Return (temporary);

}

Invalid master (invalid)

{

TMOD = 0x 0 1；

TH0 =(65536-4000)/256；

TL0 =(65536-4000)% 256；

ET0 = 1；

EA = 1；

while(resetpulse())。

writecommandtods 18b 20(0x cc)；

writecommandtods 18b 20(0x 44)；

TR0 = 1；

while( 1)

{

}

}

Void t0(void) uses 0 interrupt 1

{

Unsigned character x;

Unsigned integer result;

TH0 =(65536-4000)/256；

TL0 =(65536-4000)% 256；

if(displaycount==2)

{

P0 = display code[display buf[display count]]| 0x 80；

}

other

{

P0 = display code [displaybuf [displaycount]];

}

P2 = display bit[ display count];

display count++；

if(displaycount==8)

{

display count = 0；

}

time count++；

if(timecount== 150)

{

time count = 0；

while(resetpulse())。

writecommandtods 18b 20(0x cc)；

writecommandtods 18b 20(0x be)；

read data[0]= readdatafromds 18b 20()；

read data[ 1]= readdatafromds 18b 20()；

for(x = 0； x & lt8; x++)

{

display buf[x]= 16；

}

sflag = 0；

if((read data[ 1]& amp； 0xf8)！ =0x00)

{

sflag = 1；

read data[ 1]= ~ read data[ 1]；

read data[0]= ~ read data[0]；

Result = readdata [0]+1;

Read data[0]= result;

If (result & gt255)

{

read data[ 1]++；

}

}

read data[ 1]= read data[ 1]& lt； & lt4;

readdata[ 1]= readdata[ 1]& amp； 0x70

x = read data[0]；

x = x & gt& gt4;

x = x & amp0x0f

read data[ 1]= read data[ 1]| x；

x = 2；

result = readdata[ 1]；

While (result/10)

{

Display buf[x]= result%10;

Result = Result/10;

x++；

}

Display buf[x]= result;

if(sflag== 1)

{

display buf[x+ 1]= 17；

}

x = read data[0]& amp； 0x0f

x = x & lt& lt 1;

display buf[0]=(dot code[x])% 10；

display buf[ 1]=(dot code[x])/ 10；

while(resetpulse())。

writecommandtods 18b 20(0x cc)；

writecommandtods 18b 20(0x 44)；

}

}