Temperature control is widely used in some areas, but most of the existing temperature sensing element for the Analog Devices (thermocouple) bulky, complex applications, but not easy to achieve digital and other shortcomings, hindered the expansion of application fields. Practical application of this design were selected from small, relatively high accuracy digital temperature sensor for temperature measurement, microcontroller as a master chip, LCD as the display output. Achieve real-time temperature measurement and control. The design of the existing environment can display time and temperature, and can be set upper and lower temperature alarm value, may also need time for temperature control. This is a single chip integrated circuit design applications. It contains the LCD display interface, keyboard interface man-machine communication, single-bus temperature sensor chip. LCD display screen which used NOKIA 3310 cell phone screen as a display output, the cell phone screen a large number of stock in the country, and the higher cost, the application is also very convenient. The circuit is novel, practical, is a good beginners introduction to SCM issues. First, the working principle is shown in Figure 1, the circuit is the most commonly used market, the 8-bit microcontroller AT89C52 as the master chip, through P2.0, P2.1, P2.2, P2.3 port software to simulate the way SPI port and the LCD module control chip LPH7366 serial communication. DS18B20 by P0.0 and single-bus communication. P1.5, P1.6, P1.7 as an output control port, control of piezoelectric ceramics, respectively, LED light-emitting diodes and relays. The value of the basic idea of ??the design of the thermometer: is to DS18B20 as the temperature sensing element, the ambient temperature data into a digital signal sent to the AT89C52, AT89C52 internal operations through the program will convert a good temperature data sent to the LCD display. The design in real-time display on the LCD temperature and time data, by showing the user can accurately know that the ambient temperature and time of real-time information, through which information users can easily control the load. The program has time timer timing control can be achieved through the time control the load in a certain temperature range. Another program also increased the temperature alarm function, the first user through the keyboard interface to set the temperature of the upper and lower limit values, set time after the program will check whether the outside temperature at the time set on the lower limit temperature value. If you exceed the load will be cut off the alarm or to stop its work. This achieved the dual control of temperature and time. Temperature control can be applied to the general area: big tent vegetables, eggs, hatching temperature can also be used as a home digital thermometer. In addition the design also left a number of I / O ports, users can also own their own needs for system expansion. U2: NOKIA 3310 mobile phone display screen, which integrates the display control module. PHILIPS control module for the company's LPH7366, the display screen in the processing factory will be bundled with this module is integrated in the display screen, so long as the user's control commands that LPH7366 can easily control the LCD display. On the screen the user will be able to facilitate the application of some process, Figure 2 for the new phone bought the screen and pin diagram, Figure 3 shows the status of self-processed map, and the huge LCD screen in the domestic stock and the price cheap easy to buy. So as a general hand-held device is suitable for display output.
U5: DS18B20 DALLAS introduced in the United States as a monolithic integrated temperature sensor as shown in Figure . It is small, the interface simple and easy to use and so on. The sensor uses a single bus interface, the measured temperature range: -55 ~ +125 , the accuracy can reach 0.0675 (12-bit sample values), the maximum temperature conversion time is 200ms. Figure 5 is a diagram of the design application.
Power running, LCD will show the boot screen. Shown in Figure , the operation frame contains a number of information. Where the temperature is displayed as the current temperature value, the value changes according to ambient temperature changes, the bottom of the display for the time display, the user can set the current time of its re-initialization time is 00:00:00. Time display of the asterisk (*) indicates whether the alarm settings, there is the show, no not displayed. The right of the screen is a graphic thermometer, it animates the display shows the current temperature value, temperature display range is set to be +37 ~ -37 . Also in the top left of the interface also adds a human face graphics, set the user through the process of facial expression can be freely modified. Other specific function setting screen shown in Figure .
The hardware design of the keyboard with separate keyboard circuit, in software development, multi-level menu on the way keyboard. Specific operation of the keyboard shown in Figure . First, power on, the keyboard function as the main menu features: KEY1: null, KEY2: time function of the set, KEY3: Set the temperature function, KEY4: backlight control, KEY5: alarm control. By KEY2 and KEY3 can enter the time function, respectively, feature set and temperature settings. After the keyboard functions by KEY2 time functions: KEY1: null, KEY2: null, KEY3: time function of the switch, KEY4: backlight control, KEY5: OK. After the keyboard functions by KEY3 function of temperature: KEY1: null, KEY2: null, KEY3: temperature function switch, KEY4: backlight control, KEY5: OK. If the function needs to be set when switching function is selected, press the OK button will be able to reset the function. Function or temperature function for the time setting operation of the keyboard are the same, time setting operation and temperature setting KEY1: Value +, KEY2: numerical -, KEY3: functional bit switch, KEY4: Backlight Control , KEY5: to identify and return to the main menu functions. Second, the software design software using the C language readable, after KeilC compile, to modular programming, structured design. Each device has its own separate driver for easy understanding. The main work flow shown in Figure .