1、电动小车遥控器的设计外文翻译毕业设计（论文）外文翻译毕业设计（论文）题目：电动小车遥控器的设计 外文题目：How to Simplify the Interface between Microcontroller and Temperature Sensor译文题目：微控制器与温度传感器接口的简化学生姓名： 金书宇 专 业： 测控技术与仪器 指导教师： 周彬 How to Simplify the Interface between Microcontroller and Temperature SensorAbstract:Temperature is an analog quantity,
2、 but digital systems often use temperature to implement measurement, control, and protection functions. If you apply the right techniques and components, the necessary conversion of analog temperature to digital information wont be difficult. This application note discusses thermal comparators, PWM-
3、output temperature sensors, and remote diode (or thermal diode) temperature sensors. Reading temperature with a microcontroller (C) is simple in concept. The C reads the output code of an analog-to-digital converter (ADC) driven by a thermistor-resistor voltage divider, analog-output temperature sen
4、sor, or other analog temperature sensor (Figure 1). The ADC built into some controllers can simplify this design. ADCs require a reference voltage, which can be generated by an external device. For example, the reference voltage for a thermistor sensor is usually the same as that applied to the top
5、of the resistor-thermistor voltage divider. However, the following complications can arise in these systems:1.The sensors output-voltage range is significantly smaller than the ADCs input-voltage range. A typical ADC for this purpose might have 8-bit resolution and a 2.5V reference voltage, which is
6、 normally equivalent to the input-voltage range. If the sensors maximum output for the temperature range of interest is only 1.25V, the effective resolution drops to 7 bits. To achieve 8-bit resolution, either add gain via an external op amp or lower the ADCs reference voltage (which may reduce the
7、accuracy of some ADCs). 2.The error budget is tight. Combining the error from the thermistor-resistor combination or analog-sensor device with those contributed by the ADC, the amplifier offset voltage, the tolerance of gain-setting resistors, and the voltage reference error may be more error than y
8、our system can tolerate. 3.You want a linear temperature-to-code transfer function and youre using a thermistor. The transfer function for thermistors is very nonlinear, but it may be sufficiently linear over the narrow temperature range required in many applications. You can compensate for the nonl
9、inearity with a look-up table, but this approach requires resources that may not be available. 4.ADC inputs are limited. If the number of temperatures you want to measure exceeds the number of ADC inputs available, you may need to add a multiplexer, which will increase the cost and development time.
10、 5.The number of C I/O pins is limited. This wont be an issue for an internal ADC, but an external serial ADC will require two to four I/O pins as an interface to the C. Figure 1. In this simple interface, the ADCs reference voltage is derived from the power-supply voltage. An analog temperature sen
11、sor can replace the thermistor-resistor voltage divider. In that case, the ADC (which can be internal to the C) requires a reasonably accurate voltage reference. The design problems are simplified if you use a temperature sensor with a digital interface. Similarly, temperature sensors with time- or
12、frequency-based outputs can alleviate the measurement problem when ADC inputs and C I/O pins are in short supply (Figure 2). The MAX6576 temperature sensor, for example, produces an output square wave whose period is proportional to absolute temperature. It comes in a 6-pin SOT23 package that requir
13、es very little board space. A single I/O pin interfaces this device to a C; after its internal counter measures the period, the C calculates the temperature. .Figure 2. The MAX6576 produces a square wave with period proportional to absolute temperature; the MAX6577 produces an output frequency propo
14、rtional to temperature. The resulting proportionality constant is set to one of four values by the TS0 and TS1 pins. No external components are necessary.Applying either ground or the positive supply voltage to each of two logic inputs selects one of four period/ temperature proportionality constant
15、s between 10s/K and 640s/K. A related temperature sensor (MAX6577) generates an output square wave whose frequency/temperature factor is programmable between 0.0675Hz/K and 4Hz/K. Both devices simplify temperature acquisition by reducing the required PC board real estate, component count, and analog
16、/digital I/O resources. They transmit temperature data to the C through a single digital I/O pin, and the addition of a single optical isolator makes them ideal for applications that require electrical isolation between the sensor and the CPU. For measuring multiple temperatures at various locations
17、, the choices become more complicated. Thermistors or conventional analog sensors can be placed in appropriate locations and connected to the ADC inputs, provided the ADC has sufficient inputs available. As an alternative, the MAX6575 transmits temperature data directly to the C; as many as eight MA
18、X6575s can be connected to a single C I/O input. A single I/O trace connects the C to these eight MAX6575s (Figure 3). To measure temperature, the C briefly pulls the I/O line low, and after a short delay the first MAX6575 also pulls the I/O line low. This time delay is proportional to absolute temp
19、erature, with a proportionality constant programmed using two pins on the MAX6575. Figure 3. Using a delay scheme to encode temperature information, multiple MAX6575s transmit up to eight temperatures to the C through a single digital I/O pin.The first sensor holds the line low for a period proporti
20、onal to temperature (5s/K) and then releases it. After a second time delay, selected by setting the programming pins for a larger proportionality constant, the second MAX6575 pulls the I/O low and holds it for an interval defined by 5s/K. Four MAX6575s can be connected to the I/O line this way. Four
21、 more MAX6575s of the other, longer-delay version can be added to the same I/O line. The MAX6575L has delay multipliers ranging from 5s/K to 80s/K, and the MAX6575H delay multipliers range from 160s/K to 640s/K. Thus, as many as eight MAX6575s can be located in different places around the system, co
22、nnected to the C by a single I/O line.For some systems, the information needed is not the exact temperature, but whether the temperature is above or below a specific value. This information can trigger a cooling fan, air conditioner, heater, or other environmental-control element. In system-protecti
23、on applications, an overtemperature bit can trigger an orderly system shutdown to avoid losing data when the system power is cut off. This single bit of information can be obtained by measuring temperature as in the examples above, but that approach requires more software and hardware than the funct
24、ion demands. Replacing the ADC in Figure 1 with a voltage comparator produces a simple 1-bit output that can drive a single I/O pin on the C (Figure 4). Again, the thermistor shown can be replaced by an analog voltage-output temperature sensor. Most such devices have a relationship between temperatu
25、re and output voltage that is unaffected by supply voltage. To preserve immunity from supply-voltage variations, connect the top of the comparators resistor-divider to a voltage reference instead of the supply voltage.Figure 4. Combining a sensor with a comparator yields a 1-bit digital output that
26、can warn the C of temperature excursions beyond a predetermined threshold or trip point. The system can be simplified by replacing the sensor-comparator combination with a thermal switch like the MAX6501. This monolithic device combines the functions of a sensor, comparator, voltage reference, and e
27、xternal resistors. When temperature exceeds the preset trip level, the open-drain output goes low. Some devices in this family have open-drain outputs that go low when temperature falls below the trip point (MAX6503), and others have push/pull outputs that go high when temperature goes either above
28、or below the trip point (MAX6502, Figure 5, or MAX6504). In addition, the hysteresis can be set to 2C or 10C by connecting a package pin to V+ or ground. The available trip temperatures range from -45C to +115C in 10C increments.Figure 5. The MAX6502 produces a logic-high output when its temperature
29、 exceeds the preset threshold value.As with the MAX6575, connecting several MAX6501s or MAX6503s to a single I/O trace enables the C to be notified when temperature crosses the threshold at one or more locations. If the system must know which location has crossed the threshold, each switch output mu
30、st be connected to a separate I/O pin.These sensors measure their own die temperatures, and because die temperature closely tracks lead temperature, each sensor should be placed so its leads assume the temperature of the component being monitored. In some cases, however, you must measure a temperatu
31、re not tightly coupled to the sensorsuch as that of a power ASIC, whose die can be much hotter than the surrounding board. An internal temperature sensor may enable the ASIC to shut itself down in response to a temperature fault, but that capability alone lacks accuracy, and it seldom warns the syst
32、em of an impending thermal overload. By adding an externally accessible p-n junction to the ASIC die, you can measure die temperature directly by forcing two or more different forward currents through the sensing junction and measuring the resulting voltages. The difference between the two voltages is proportional to the absolute die temperature:Where I1 and I2 are the two current levels forced through the p-n junction, V1 and V2 are the resulting forward voltages across the junction, k is Boltzmanns constant, T is the absolute temperature of the
