Hygrometer design based on 8051 microcontroller development

　　In this article, a microcontroller development engineer shares a hygrometer developed based on an 8051 microcontroller. This solution is relatively simple for microcontroller beginners to learn.

　　The humidity sensor is also called a hygrometer. In this microcontroller solution, its circuit can sense relative humidity (RH) from 20% to 95% with an accuracy of 5%, and the humidity information can be displayed on a 16×2 LCD display. In addition, in this microcontroller solution, a relay is also provided, which means that when the humidity exceeds a certain jump point, the relay will be activated to perform certain operations.

　　1. DHT11 humidity sensor

　　DHT11 is a low-cost humidity and temperature sensor with digital output. The capacitance method is used to sense humidity, while the thermistor is used to measure temperature. The sensor can sense relative humidity from 20% to 95% with 5% resolution. Temperature measurement up to 50°C with 2°C resolution. Communication with the microcontroller is via a single wire. The following figure shows the basic communication scheme:

　　Communicating back and forth to the DHT11 sensor is very easy. Pin 2 of DHT11 is connected to the port pin of the microcontroller. The connection scheme is shown in the figure below. The data pin (pin 2) of DHT11 requires an external 10K pull-up resistor.

　　The principle of its communication protocol is as follows. The microcontroller first sends a low-level signal with a width of 18mS to DHT11. After receiving this signal, the microcontroller pulls up the communication line and waits for the response of DHT11. It takes 2 to 40uS at most. Then DHT11 pulls the communication line low and keeps it low for 80usS. Then DHT11 pulls the line high and keeps it high for 80uS. DHT then pulls the line low for 50uS and the next high pulse will be the first bit of data. Data is sent in bursts of 8 bits. Each high pulse of the pulse train represents a data signal. The 50uS low signal between data bits is just a gap. The logic of a data bit is determined by measuring its width. A 26 to 28uS wide pulse indicates "low", while a 70uS wide pulse indicates "high". Simply put, pulses narrower than 50uS can be considered "low" and pulses wider than 50us can be considered "high". The first 8 bits of the data burst represent the integer value of relative humidity, the last 8 bits represent the decimal value of relative humidity, the last 8 bits represent the integer value of temperature data, and the last 8 bits represent the decimal value. For DHT11, the decimal value is always zero, we Relative humidity is measured only in this scenario. Therefore, we only need to focus on the first 8 bits of the data, which are the components of the relative humidity data. The figure below shows the circuit diagram of the humidity sensor. The last 8 bits represent the decimal value of the relative humidity, the last 8 bits represent the integer value of the temperature data, the last 8 bits represent the decimal value of the temperature data, for DHT11 the decimal value is always zero, we are measuring relative humidity only in this scenario . Therefore, we only need to focus on the first 8 bits of the data, which are the components of the relative humidity data. The figure below shows the circuit diagram of the humidity sensor. The last 8 bits represent the decimal value of the relative humidity, the last 8 bits represent the integer value of the temperature data, the last 8 bits represent the decimal value of the temperature data, for DHT11 the decimal value is always zero, we are measuring relative humidity only in this scenario . Therefore, we only need to focus on the first 8 bits of the data, which are the components of the relative humidity data. The figure below shows the circuit diagram of the humidity sensor. Therefore, we only need to focus on the first 8 bits of the data, which are the components of the relative humidity data. The figure below shows the circuit diagram of the humidity sensor. Therefore, we only need to focus on the first 8 bits of the data, which are the components of the relative humidity data. The following figure shows the circuit diagram of the humidity sensor:

　　The humidity sensor DHT11 is connected to P3.1 of the 8051 microcontroller. R8 pulls up the communication line between DHT11 and 8051. This relay is driven by P2.0 of the microcontroller. Transistor Q1 switches the relay. R0 is the pull-up resistor, and R7 limits the base current of Q1. D5 is just a freewheeling diode. The data line of the LCD display is connected to port 0 of the microcontroller. The control lines RS, R/E and E are connected to the P2.7, P2.6 and P2.5 pins of the microcontroller respectively. R4 sets the contrast of the display. R5 limits the current flowing through the backlight LED. C9 is a bypass capacitor. C8, C10 and X1 are associated with the clock circuit. C11, R6 and S2 form the reset circuit.

　　2. Source code

　　RS EQU P2.7

　　RW EQU P2.6

　　EEQU P2.5

　　ORG 000H

　　MOV DPTR, #LUT

　　SETB P3.5

　　CLR P2.0

　　MOV TMOD, #00100001B

　　MOV TL1, #00D

　　ACALL DINT

　　ACALL TEXT1

　　MAIN: MOV R1, #8D

　　SETB P3.5

　　CLR P3.5

　　ACALL DELAY1

　　SETB P3.5

　　HERE:JB P3.5, HERE

　　HERE1:JNB P3.5,HERE1

　　HERE2:JB P3.5, HERE2

　　LOOP: JNB P3.5, LOOP

　　RL A

　　MOV R0,A

　　SETB TR1

　　HERE4:JB P3.5, HERE4

　　CLR TR1

　　MOV A, TL1

　　SUBB A, #50D

　　MOV A,R0

　　JB PSW.7, NEXT

　　SETB ACC.0

　　SJMP ESC

　　NEXT:CLR ACC.0

　　ESC: MOV TL1, #00D

　　CLR PSW.7

　　DJNZ R1,LOOP

　　ACALL DINT

　　ACALL TEXT1

　　ACALL LINE2

　　ACALL TEXT2

　　ACALL HMDTY

　　ACALL CHECK

　　ACALL DELAY2

　　LJMP MAIN

　　DELAY1: MOV TH0, #0B9H

　　MOV TL0, #0B0H

　　SETB TR0

　　HERE5: JNB TF0, HERE5

　　CLR TR0

　　CLRTF0

　　RET

　　DELAY2:MOV R1, #112D

　　BACK:ACALL DELAY1

　　DJNZ R1,BACK

　　RET

　　CHECK:MOV A, R0

　　MOV B, #65D

　　SUBB A, B

　　JB PSW.7,NEXT1

　　ACALL TEXT3

　　SETB P2.0

　　SJMP ESC1

　　NEXT1:ACALL TEXT4

　　CLR P2.0

　　ESC1:CLR PSW.7

　　RET

　　CMD: MOV P0,A

　　CLR RS

　　CLR RW

　　SETB E

　　CLR E

　　ACALL DELAY

　　RET

　　DISPLAY:MOV P0,A

　　SETBRS

　　CLR RW

　　SETB E

　　CLR E

　　ACALL DELAY

　　RET

　　HMDTY:MOV A, R0

　　MOV B, #10D

　　DIV AB

　　MOV R2, B

　　MOV B, #10D

　　DIV AB

　　ACALL ASCII

　　ACALL DISPLAY

　　MOV A, B

　　ACALL ASCII

　　ACALL DISPLAY

　　MOV A,R2

　　ACALL ASCII

　　ACALL DISPLAY

　　MOV A,#"%"

　　ACALL DISPLAY

　　RET

　　TEXT1: MOV A,#"H"

　　ACALL DISPLAY

　　MOV A,#"y"

　　ACALL DISPLAY

　　MOV A,#"g"

　　ACALL DISPLAY

　　MOV A,#"r"

　　ACALL DISPLAY

　　MOV A,#"o"

　　ACALL DISPLAY

　　MOV A,#"m"

　　ACALL DISPLAY

　　MOV A,#"e"

　　ACALL DISPLAY

　　MOV A,#"t"

　　ACALL DISPLAY

　　MOV A,#"e"

　　ACALL DISPLAY

　　MOV A,#"r"

　　ACALL DISPLAY

　　RET

　　TEXT2: MOV A,#"R"

　　ACALL DISPLAY

　　MOV A,#"H"

　　ACALL DISPLAY

　　MOV A,#" "

　　ACALL DISPLAY

　　MOV A,#"="

　　ACALL DISPLAY

　　MOV A,#" "

　　ACALL DISPLAY

　　RET

　　TEXT3: MOV A, #" "

　　ACALL DISPLAY

　　MOV A,#" "

　　ACALL DISPLAY

　　MOV A,#"O"

　　ACALL DISPLAY

　　MOV A,#"N"

　　ACALL DISPLAY

　　RET

　　TEXT4:MOV A，#" "

　　ACALL DISPLAY

　　MOV A,#"O"

　　ACALL DISPLAY

　　MOV A,#"F"

　　ACALL DISPLAY

　　MOV A,#"F"

　　ACALL DISPLAY

　　RET

　　DINT:MOV A，#0CH

　　ACALL CMD

　　MOV A, #01H

　　ACALL CMD

　　MOV A, #06H

　　ACALL CMD

　　MOV A, #83H

　　ACALL CMD

　　MOV A, #3CH

　　ACALL CMD

　　RET

　　LINE2:MOV A，#0C0H

　　ACALL CMD

　　RET

　　DELAY: CLR E

　　CLR RS

　　SETB RW

　　MOV P0,#0FFH

　　SETB E

　　MOV A,P0

　　JB ACC.7,DELAY

　　CLR E

　　CLR RW

　　RET

　　ASCII: MOVC A, @A+DPTR

　　RET

　　LUT: DB 48D

　　DB 49D

　　DB 50D

　　DB 51D

　　DB 52D

　　DB 53D

　　DB 54D

　　DB 55D

　　DB 56D

　　DB 57D

　　END