Detailed sees the temperature sensor application in microprocessor
[introduction] what export means and interface way according to temperature sensor is different, can divide roughly for sensor of imitate temperature sensor and digital temperature. The imitate signal that imitate temperature sensor outputs, the ability after must be being changed into digital signal through special interface circuit is undertaken handling by microprocessor.
The measurement of temperature is controlled use sundry temperature sensor commonly, commonly used temperature sensor reachs his to measure lukewarm range (℃ ) for: Thermocouple (- 84 ～ 2300) , thermal resistance (- 200 ～ 850) , thermal resistor (- 55 ～ 300) , semiconductor (- 55 ～ 150) . What export means and interface way according to temperature sensor is different, can divide roughly for sensor of imitate temperature sensor and digital temperature. The imitate signal that imitate temperature sensor outputs, the ability after must be being changed into digital signal through special interface circuit is undertaken handling by microprocessor. The digital signal that digital temperature sensor outputs, need only commonly a few exterior yuan parts of an apparatus can send to microprocessor to undertake handling directly. As the flying development of the computer and semiconductor technology, temperature sensor has the semiconductor temperature sensor of digital interface to get wide application and rapid development especially.
Sensor of 1 imitate temperature
The imitate temperature sensor of 1.1 output voltage or voltaic signal
Traditional pyroelectricity side, thermal resistance,
Thermal resistor and semiconductor temperature sensor are voltage of imitate of the output after temperature the value passes certain interface circuitry to change or voltaic signal, use these voltage or voltaic signal to be able to undertake metrical controlling. If think this kind of imitate signal is changed,become the signal that microprocessor can process, need to use modulus converter to change its amount to to pile up, read by microprocessor next take can, if pursue,1 is shown.
Means of another kind of changeover is to undertake V/F alternates. V/F transformer is the oscillating circuit that an oscillation frequency changes along with control voltage and changes actually. Its characteristic is to have good precision, degree of linearity and integral input, and circuit is simple. Graph 2 for small be implement the interface circuit with V/F transformer and temperature sensor. Among them the AD654 that V/F transformer uses AD firm. Through adjusting, AD654 can output the pulse of 0 ～ 500kHz to string together, output and sheet piece the timer of machine / tally T1 is linked together have count, undertake timing with timer T0. The number that carries pair of place plan has computation and transition, current temperature is worth attainable sensor.
The main characteristic of sensor of voltage output temperature is power source voltage and electric current lower, in transmission line voltage drop and voltage noise either when main influencing factor, its voltage output can become control system and data to collect input signal of the system directly. Commonly used voltage outputs semiconductor temperature sensor to the LM35/45/50/60 of company of the TMP35/36/37 of AD company, NS waits.
In certain and special situation, need to use the temperature sensor that electric current outputs, the main characteristic of sensor of voltaic output temperature is output impedance is tall, output electric current does not suffer the effect of transmission line voltage drop and voltage noise, and have very strong inhibition to the pulse of power source voltage and drift ability. Electric current outputs temperature sensor desire with microprocessor interface when, need to turn electric current into voltage commonly, next the signal that changeover of reoccupy A/D converter can process into microprocessor. Such sensor has the AD590 of AD company, TMP17 to wait.
1.2 output jump change the imitate temperature sensor of signal
In certain system, do not need to know accurate temperature is worth, and need to understand temperature only whether prep above or under some specific value can. This information is usable will spark this kind of the control unit such as fan, air conditioning, heater, special imitate temperature sensor is output jumps only commonly change signal undertakes controlling, say normally for temperature controller.
Replace a plan with comparator of a voltage 1 medium ADC, an output of generation but an I/O line of drive small controller, if pursue,3 are shown. To avoid the effect that power source voltage changes, the door of comparator is restricted voltage is desirable from voltage voltage of power source of fiducial and rather than.
Undertake sensor and comparator combination circuitry compositive, make systematic level pace simplifies. This kind of compositive temperature controller often is called temperature switch. This kind of sheet piece parts of an apparatus combined sensor,
Comparator, voltage is fiducial wait for a variety of parts of an apparatus with necessary resistor. Set the door beforehand more than when temperature in a limited time, output n happening to jump change, control adds lukewarm or frigorific parts of an apparatus to be connected. The MAX6501/6502 of MAXIM company is hot lukewarm switch, from manufacturer 45 ℃ arrive 95 ℃ beforehand buy door of 6 kinds of temperature is restricted. MAX6503/6504 is cold lukewarm switch, its temperature door is restricted to be – 15 ℃ and 5 ℃ two kinds. MAC6501/6503 is leakage output, low n is effective, MAX6502/6504 is push-pull output, tall n is effective. After the output of MAX6501 helps resistance on classics of microprocessor of OK and direct drive interrupt or restoration, if pursue,4 are shown. The output classics of MAX6502 is simple after drive, fan of OK and direct control works. Cooperate through a few simple circuit, still can apply its at temperature window to call the police. Control of cent administrative levels. The AD22105 of such chip or AD company.
Sensor of 2 numbers temperature
Change imitate temperature sensor and number interface circuit compositive together, make the digital temperature sensor that has a number to output ability. As the swift and violent development of semiconductor technology, circuit of semiconductor temperature sensor and corresponding change-over circuit, interface and mix kind of other function circuit gradually compositive together, formed a function the digital temperature sensor of cheap of powerful, accurate, price.
The digital temperature sensor that 2.1 single track output
The characteristic of single-track output is interface circuit simple, measure the temperature that go out the value is exact, in applying commonly so, guo of this kind of world got partial. Because have an output line only, measure the temperature value that give to must be changed into some kind of means to undertake outputting. Common output means has time output, frequency output and numeric output to wait, the signal that outputs temperature sensor by microprocessor again next is changed into actual temperature to be worth, undertake be been further with control.
The temperature sensor that 2.1.1 time output
The TMP03/04 of AD company is the digital temperature sensor that commonly used time outputs. They output the rectangular wave after passing modulation, need to be measured so that its output square wave to occupy the actual time width of the T1 in comparing T1/T2 for nothing and T2 only in application, can calculate the temperature of an object that be measured. When joining with microprocessor, need to export chip the timer with microprocessor only / tally is linked together, can measure the time width that gives T1, T2 easily, calculate a corresponding temperature value. TMP03 is output of collector open a way, need to go up the person helps resistance, TMP04 is leakage output, but circuit of direct drive logic. The MAX6576 of MACIM company also is a kind of temperature sensor that exports time. The direct ratio of cycle of square wave signal that it outputs at absolutely temperature. Its interface means is shown 5 times like the graph.
The MAX6575L/H chip of MAXIM company is the temperature sensor that another kind of very convenient and practical time outputs. Its characteristic is most on an I/O line can receive 8 chip at the same time, measure 8 to nod at the same time temperature and not mutual interference. Choose different type of “L” , “H” through be being reached to the different join of pin TS0, TS1, can install chip coefficient of different delay time. When measuring temperature, microprocessor starts transition, after the delay time TDx that is worth at absolutely temperature via direct ratio, MAX6575 draws low I/O line. Through measuring TDx of time of this delay time, the delay time coefficient of this chip that recycle place installs, can calculate the temperature value that gives this chip place to measure. Because coefficient of each chip delay time is different, time of its delay time can not overlap each other, the timer of use microprocessor / the delay time time that tally can measure an each chip respectively, calculate again give each chip place to measure the temperature that go out.
The single-track temperature sensor that 2.1.2 frequency output
MAX6577 is the digital temperature sensor that outputs frequency signal. It outputs the square wave that takes sky comparing to be 1/2, its frequency direct ratio at absolutely temperature. Its internal composition and unusual appearance of use means and MAX6576 draft. The frequency that chooses comfortable collection through bringing crural TS0, TS1 / temperature scale is invariable, after measuring a frequency by the in-house tally of microprocessor again, temperature is measured after computation goes out. The interface means of its and microprocessor sees a picture 5.
The single-track temperature sensor that 2.1.3 numerical value output
The single-track temperature sensor of numeric output outputs chip to measure the specific temperature numerical value that give with serial means directly, be afraid of with meantime foreword very important. The DS1820 of DALLAS company is a kind of such distinctive temperature sensor. It needs an interface to bring a foot to be able to correspond only, power supply of available data line, have much dot to measure lukewarm ability. If the graph is shown 6 times,its hardware join reachs sequential chart. Its are read write sequential to basically have restoration, read time piece and keep time piece operation of 3 kinds of sequential. Chip itself contains order volume and memory, microprocessor commands through giving out control, undertake reading writing to chip memory, the temperature that finish is measured. Chip power source also can be offerred by the I/O mouth of small processing. Microprocessor is being read before writing DS1820, make first its restoration, detect after its reply, microprocessor sends ROM to handle an order, next reappearance dominates a command. When many bits of temperature is measured, need parallel connection only many DS1820 is put in each to measure lukewarm dot to go up, undertake to each chip before use ROM is searched and save the alignment mark of each chip rise. When finding site to every DS1820 later, want to send corresponding alignment signal only, undertake to its other is operated again next can. With DS1820 similar chip still has DS1822.
The 2.2 data temperature sensor that are based on output of bus line agreement
To raise dependability, convenient use, people designed a lot of number temperature that are based on output of agreement of some kind of bus line again sensor. Sensor of this kind of temperature has output of much root line commonly. Output format and sequential abide by some kind of agreement strictly, apply to all sorts of circumstances, especially far end is measured. Familiar consultative pattern has SMBus agreement, I2C agreement to wait.
The 2.2.1 temperature sensor that are based on SMBus bus line
The 1619 series of MAX1617 ～ of MAXIM company are to use the Yuan Duanwen of SMBus serial interface to spend sensor. MAX1619 uses the temperature of the CPU inside the PC that monitor. It through bringing to bear on electric current is measured measuring exterior PN to written guarantee to knot pressing (inside schism transistor, ASIC or CPU) the knot is lukewarm, pass SMBus second line serial interface the result (8 precision) pass microprocessor. Two lines of SMBus interface are clock line and data line respectively, if pursue,7 are shown. In use, of software write the standard that must observe SMBus agreement strictly. MAX1619 but at the same time this locality measures oneself to enclose temperature, and have fan to control output; Still but beforehand set temperature door is restricted, when temperature prep above or microprocessor is interrupted when be restricted to be worth under this. Pass pin process designing, change the join way of ADD0, ADD1, can the SMBus address that the choice differs 9 times at most, join can allow many MAX1619 to join is on same bus line and do not send an address to conflict.
The 2.2.2 temperature sensor that are based on I2C bus line
The AD7416 of AD company is to have I2C second line the sensor of temperature of number of low power comsumption of serial interface.
It passes a sensor of celestial being temperature is accurate measure environmental temperature, change serial output through 10 A/D next. It also is had set temperature to the door is restricted and interrupt output function beforehand. The minimum of address of AD7416 serial bus line chooses 3 times through pin process designing, because this is OK,on a bus line join amounts to 8 chip. Two lines of I2C are clock line and two-way data line respectively. Of in use software write the format that should abide by I2C agreement strictly and sequential.
As a result of the similar sex of SMBus interface and I2C interface, the output of the AD7414 of AD company, AD7415 at the same time compatible these two kinds of interface, more the earth went to the lavatory to use.
The 2.2.3 temperature sensor that are based on SPI interface
The AD7814 of AD company is the temperature sensor that has SPI serial interface. It can reach DSP to cooperate to use with most height processor. AD7814 and the interface way of 8051 series microprocessor are very simple, 8051 jobs are in serial interface means 0, the pin DOUT of AD7814 and SCLK are received respectively in the serial mouth P3.0 of 8051 and P3.1, DIN ground connection, CS is controlled by mouth of some data I/O, be like P1.0. Should keep data to AD7814 in order to fulfil some kind of special function when, need to use DIN pin, can use the other data port of 8051 to undertake controlling.
As the arrival that the Information Industry changes, temperature sensor especially semiconductor temperature is passed feeling because this gets further progress,dare meet. Sensor of digital semiconductor temperature because its are cheap, accurate, linear, low the characteristic such as power comsumption, miniaturization is sure to get greater progress.