The read/write operations of the LCD1602 liquid crystal module, the operations of the display screen and the cursor are all implemented through instruction programming (where 1 is high level and 0 is low level), They are introduced separately as follows.
(1) Command 1: Clear the screen. Instruction code 01H, the cursor is reset to address 00H.
(2) Instruction 2: Cursor reset. The cursor is reset to address 00H.
(3) Command 3: Input mode setting. Among them, I/D represents the moving direction of the cursor, high level moves right, low level moves left; S represents whether all the text on the display screen moves left or right, high level means valid, and low level means invalid.
(4) Command 4: Display switch control. Among them, D is used to control the on and off of the overall display. High level indicates that the display is on, and low level indicates that the display is off. C is used to control the on and off of the cursor. High level indicates that there is a cursor, and low level indicates that there is no cursor. ;B is used to control whether the cursor flashes, high level flashes, low level does not flash.
(5) Instruction 5: Cursor or character shift control. Among them, S/C means moving the displayed text when the level is high, and moving the cursor when the level is low.
(6) Command 6: Function setting command. Among them, DL means that it is a 4-bit bus at high level and 8-bit bus at low level; N means that it is a single line display at low level and double line display at high level; F means that it displays 5×7 points at low level. Matrix characters, 5×10 dot matrix characters are displayed when the level is high.
(7) Instruction 7: Character generator RAM address setting.
(8) Instruction 8: DDRAM address setting.
(9) Instruction 9: Read busy signal and cursor address. Among them, BF is the busy flag. If it is high, it means busy. At this time, the module cannot receive commands or data. If it is low, it means it is not busy.
(10) Instruction 10: Write data.
(11) Instruction 11: Read data.
****Temperature sensor DS18B20: **** ** 1. Introduction
DS18B20 temperature sensor is an improved intelligent temperature sensor launched by DALLAS Semiconductor Company in the United States. Compared with traditional thermistors, it can directly read By outputting the temperature, it can complete the collection and conversion of temperature signals. This sensor transmits the collected temperature to the microcontroller through the data pin.
2. Performance characteristics
(1) Unique single-wire interface method, DS18B20 only needs one port line when connecting to the microprocessor to achieve two-way communication between the microprocessor and DS18B20.
(2) Temperature measurement range -55℃～+125℃, inherent temperature measurement error is 1℃.
(3) Support multi-point networking function, multiple DS18B20 can be connected in parallel on the only three lines, up to 8 can be connected in parallel to achieve multi-point temperature measurement. If there are too many, the power supply voltage will be too low, resulting in signal Transmission instability.
(4) Working power supply: 3.0~5.5V/DC (data line parasitic power can be used)
(5) No external components are required during use
(6) The measurement results are transmitted serially in a 9~12-digit digital format
(7) The diameter of the stainless steel protective tube is Φ6
(8) Suitable for temperature measurement of DN15~25, DN40~DN250 various medium industrial pipelines and narrow space equipment
(9) Standard installation threads M10X1, M12X1.5, G1/2" optional
(10) PVC cable outlet directly or German ball junction box outlet, easy to connect with other electrical equipment.
3. Working principle
of DS18B20 reading and writing timing and temperature measurement The principle is the same as that of DS1820, except that the number of digits of the temperature value obtained is different due to different resolutions, and the delay time during temperature conversion is reduced from 2s to 750ms. The oscillation rate of the high temperature coefficient crystal oscillator changes significantly as the temperature changes, and the resulting The signal is used as the pulse input of counter 2. Counter 1 and the temperature register are preset at a base value corresponding to -55°C. Counter 1 subtracts the pulse signal generated by the low temperature coefficient crystal oscillator. When the preset value of counter 1 decreases When it reaches 0, the value of the temperature register will be increased by 1, the preset of counter 1 will be reloaded, and counter 1 will restart counting the pulse signals generated by the low temperature coefficient crystal oscillator. This cycle will stop when counter 2 counts to 0. The temperature register value is accumulated. At this time, the value in the temperature register is the measured temperature. The slope accumulator in the figure is used to compensate and correct the nonlinearity in the temperature measurement process, and its output is used to correct the preset value of counter 1.
! [QQ picture 20200726233144.png] 
4. Control method
(1) Control command
Temperature conversion* * 44H Start DS18B20 for temperature conversion
and read scratchpad * * BEH Read scratchpad 9-byte binary number
Write scratchpad * * 4EH Write data to the TH and TL bytes of the temporary register.
Copy the temporary register* * 48H Write the TH and TL bytes of the temporary register to the E2PROM
and re-adjust the E2PROM * * B8H Write the TH and TL bytes in the E2PROM to the temporary register TH and TL bytes.
Read the power supply mode* * B4H 启动DS18B20发送电源供电方式的信号给主CPU
（2）初始化
在初始化序列期间，总线控制器拉低总线并保持480us（改延时可以在480~960us之间，但需要在480us以内释放总线）以发出一个复位脉冲，然后释放总线，进入接收状态（等待DS18B20应答）。总线释放后，单总线由上拉电阻拉到高电平。当DS18B20探测到I/O引脚上的上升沿后，等待15-60us，然后其以拉低总线60-240us的方式发出存在脉冲。至此，初始化时序完毕。
![QQ图片20200726233227.png]
（3）写时序
主机在写时隙向DS18B20写入数据，其中分为写”0”时隙，和写”1”时隙。总线主机使用写“1”时间隙向DS18B20写入逻辑1，使用写“0”时间隙向DS18B20写入逻辑0.所有的写时隙必须有最少60us的持续时间，相邻两个写时隙必须要有最少1us的恢复时间。
![QQ图片20200726233245.png]
![QQ图片20200726233259.png]
（4）读时序
主机发起读时序时，DS18B20仅被用来传输数据给控制器。因此，总线控制器在发出读暂存器指令［0xBE］或读电源模式指令［0xB4］后必须立刻开始读时序，DS18B20可以提供请求信息。除此之外，总线控制器在发出发送温度转换指令［0x44］ （或召回EEPROM指令［0xB8］）之后读时序。
所有读时序必须最少60us，包括两个读周期间至少1us的恢复时间。当总线控制器把数据线从高电平拉到低电平时，读时序开始，数据线必须至少保持1us，然后总线被释放。DS18B20 通过拉高或拉低总线上来传输”1”或”0”。当传输逻辑”0”结束后，总线将被释放，通过上拉电阻回到上升沿状态。从DS18B20输出的数据在读时序的下降沿出现后15us 内有效。
![QQ图片20200726233445.png]
![图片2.png]
![图片3.png]
****1.显示模块********
![图片5.png]
由两个LED报警提示和一个蜂鸣器组成，温度超过设定最高温度时D2亮，蜂鸣器报警；温度低于设定最低温度时D1亮，蜂鸣器报警。
****3.供电模块****
![图片8.png]
Use four 1.5V batteries and a 7805 three-terminal voltage stabilizing integrated circuit as the power module, add two grounding capacitors to filter the AC component, and the out is about 5V.
![Picture 9.png] 
Considering that the working voltage of the LCD display and WIFI module is 5V, and the working voltage of the microcontroller is 3.3V, a 3.3V voltage stabilizing chip is connected in series to the output terminal OUT of the original power module, which can stabilize the 5V voltage of the battery power supply. to 3.3V.
When the line is connected, the 5V working voltage module uses the OUT terminal for power supply, and the 3.3V working voltage module uses the VOUT terminal for power supply.
****4.WIFI module**** ![Picture 10.png] 
The working voltage of the ESP-01S chip is 5V, so it is powered by the IN terminal of the power supply.
Communicates serially with the microcontroller and sends data to the PC.
****5. Temperature acquisition module**** ![Picture 11.png] 
Key function description:
SET:
Press once SET: Set Upper limit temperature
Press SET twice: Set the lower limit temperature
ADD: Add one to the set temperature value
SUP: Subtract one from the set temperature value
RETURN: Return to the temperature display interface
**6, ******Simulation test**** * ** ****Temperature display function test: **** ** (1) Turn on the system switch and set the ambient temperature to 25°C
! [Picture 13.png] 
(2) Observe the LCD screen for 1s Then it responds to the temperature change and displays 20°C
! [Picture 14.png] 
(2) Use the buttons to modify it
so that the upper and lower limits are 35°C and 15°C
![Picture 16.png] 
****Dangerous temperature alarm function test: ****** ** (1) Over the upper limit
! [Picture 17.png] 
Experimental results:
! [Picture 18.png] 
The high temperature alarm LED turns on and emits light, the buzzer P10 port forms a high potential, and the buzzer alarms
(2) Beyond the lower limit
! [Picture 19.png] 
Experimental results:
! [Picture 20.png] 
The low temperature alarm LED is turned on and emits light, the buzzer P10 port forms a high potential, and the buzzer alarms.
Simulation test results: The function is in line with expectations.
**7. ******Physical test adjustment****** ** (1) The working voltage of each device is not uniform, and the same current source cannot be used.
Solution:
Add two voltage stabilizing chips
l 7805 voltage stabilizing chip to stabilize the battery power supply voltage to 5V
l SSP-1117 voltage stabilizing chip to stabilize the 5V voltage to 3.3V
Different devices will use different power supply ports (5V / 3.3V) , each module has achieved normal operation
. At the same time, in the voltage stabilizing chip module, we also configured a grounding capacitor to derive the AC component to make the system work more stable.
(2) Abnormal LCD display.
After voltage probe testing, it was found that the voltage of the LCD module was too high.
Solution:
Adjust the LCD module pull-up resistor. After adjustment, the LCD displays normally.
(3) Circuit welding:
Due to weak soldering of the circuit, the system could not work normally, and it was found after investigation. During the physical welding process, attention should be paid to checking for virtual soldering and pin short circuits caused by errors during the welding process. Especially when welding microcontrollers and integrated chips, due to their small pins and dense arrangement, they need to be operated very carefully and checked in time.
(4) Microcontroller switching circuit.
It was originally considered to place an LED light display in the switching circuit of the microcontroller and connect a resistor in series to divide the voltage to prevent the voltage at both ends of the LED from being too high and burning out the LED. However, after welding, it was found that the output voltage was lower than the operating voltage of the microcontroller due to the voltage reduction of the LED. After consideration, the LED and resistor of the switch circuit were deleted and replaced with wire connections.
(5) Buzzer voltage adjustment
During the test, it was found that the output voltage of the buzzer corresponding to the microcontroller pin was too low, resulting in an inconspicuous sound of the buzzer. After considering several solutions, the buzzer was adjusted. The way of voltage is so that the voltage of the buzzer will not be too low when the output voltage of the corresponding pin of the microcontroller is low level, and at the same time, the buzzer will respond normally when the pin outputs high level.
The following is the component list: (The components used are all products from Lichuang Mall) ![Picture 21.png] 
**8. ******Summary and Reflection****** ** In this electronic In the design practice, we completed the design of a temperature monitoring system based on a single-chip microcomputer. We have a deeper understanding of the structure and functions of microcontrollers, learned and experienced the process of system experiments, and felt the infinite charm of electronic information technology. The portable temperature monitoring system we designed and implemented has a simple structure, is easy to transplant, and has certain practical value.
At the same time, there are still many areas for improvement in this system, such as the maximum measured temperature of 99°C and the large remote monitoring distance limit. In future study and practice, we will continue to improve our own quality and improve product performance so that it can be better used in people's production and life.
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