<\/p>\n\n\n\n
RT<\/sub>: Typical application circuit recommended in the short cable length of 20m on the 5.1k\u03a9 pull-up register, the resistance of greater than 20m under the pull-up resistor on the lower actual situation. To get the temperature and humidity data we need 3 steps. Let\u2019s look at all steps one by one<\/p>\n<\/div>\n\n\n\n Here the pulse width of 26\u00b5s ~ 28\u00b5s indicates a bit 0 and 70\u00b5s represent bit 1. We measure the pulse using External Interrupt and timer. We enable external interrupt at any edge. Let\u2019s look at the program below for simplicity-<\/p>\n\n\n\n Let\u2019s use timer0 with prescaler 8. So the new frequency & time of timer0 is<\/p>\n\n\n\n \u0192timer0<\/sub> = 8MHz\/8 = 1MHz & Ttimer0<\/sub> = 1\u00b5s<\/p>\n\n\n\n TCNT0 value will determine the pulse width value. <\/p>\n\n\n\n Look at the interrupt service routine function for more details \u2013<\/p>\n\n\n We have found the bit, now it is time for calculation-<\/p>\n\n\n\n Constant variable<\/strong>: const is used with a data type declaration or definition to specify an unchanging value.<\/p>\n\n\n\n Const objects may not be changed.<\/p>\n\n\n\n Volatile variable<\/strong>: Volatile specifies a variable whose value may be changed by process outside the current program. One example of a volatile object might be a buffer used to exchange data with an eternal device.<\/p>\n\n\n\n In our program we declare volatile uint16_t data_packet[40]; and volatile float humidity,temperature; global variable which can be used in any .c file.<\/p>\n\n\n\n Let\u2019s back to our main program. Sensor transmit a total of 40bits containing the temperature and humidity.<\/p>\n\n\n\n So that the humidity is byte1+byte2*0.1 and in temperature calculation the 7th<\/sup> bit of fractional data byte represent the positive and negative sign. If 7th<\/sup> bit is 1 temperature is positive and if it is 0 then temperature is positive.<\/p>\n\n\n Here timer2 is initialized at 250ms to call sensor at every 5s. So the data will be update in every 5s. One interesting thing that we use %02d to display only 2digit of temperature and humidity data. <\/p>\n\n\n\n![\"\"](\"https:\/\/iotthinghub.com\/wp-content\/uploads\/2024\/06\/DHT11-sensor.jpg\")
<\/figure>\n<\/div>\n<\/div>\n\n\n\n![\"\"](\"https:\/\/iotthinghub.com\/wp-content\/uploads\/2024\/06\/image-3-923x1024.png\")
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<\/figure>\n\n\n\n void init_dht11(void)\n {\n DDRD|=(1<<DDD2); \/\/DD2 for read data\n PORTD|=(1<<PORTD2); \/\/Output high\n PORTD&=~(1<<PORTD2); \/\/Ouput Low for 18ms\n _delay_ms(18);\n PORTD|=(1<<PORTD2); \/\/Output high for relise bus\n DDRD&=~(1<<DDD2); \/\/Input sate declear for interrupt triger\n while(PIND&(1<<PIND2));\/\/Wait for pull the data line low\n while(!(PIND&(1<<PIND2)));\/\/wait 80us low\n while(PIND&(1<<PIND2)); \/\/wait 80us high\n while(!(PIND&(1<<PIND2)));\/\/wait 50us low\n sei();\n \/\/SREG|=(1<<I);\t \/\/Global interrupt enable\n GICR |=(1<<INT0);\t \/\/External Interrupt Request 0 Enable\n MCUCR|=(1<<ISC00);\t \/\/any edge of INT0 generates an interrupt request\n }\n<\/pre><\/div>\n\n\n![\"\"](\"https:\/\/iotthinghub.com\/wp-content\/uploads\/2024\/06\/pulse-width-1024x250.jpg\")
<\/figure>\n\n\n\n\n uint8_t start_flag=1,millisecond;\n\/**** Interrupt service routine ********************\/\nISR(INT0_vect)\n{ \n if(start_flag){\n\t\tpulse=TCNT0;\n\t\tTCCR0=0; \/\/ Timer stop\n\t\tif(pulse<30) sample[count]=0;\n else if(pulse>50 && pulse<75) sample[count]=1;\n count++;\n start_flag=0;\n }else{ \/\/ start timer with flag clear\n TCCR0|=(1<<CS01); \/\/prescaler 8\n TCNT0=0; \/\/intialize timer value\n start_flag=1;\n }\nif(count>40) \n\t{\n\t\tcount=0;\n\t\tstart_flag=1;\n\t}\n}\n<\/pre><\/div>\n\n\n![\"\"](\"https:\/\/iotthinghub.com\/wp-content\/uploads\/2024\/06\/c-structure-1.jpg\")
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![\"\"](\"https:\/\/iotthinghub.com\/wp-content\/uploads\/2024\/06\/DHT-byte-1024x171.jpg\")
<\/figure>\n\n\n\n\n\/************************************************************************************************\n*************************************************************************************************\nThis program will read the temperature and humidity data and display in LCD\n The value sould be update in every 5s\n \n*************************************************************************************************\n\t\tSubeer Kumar Sarkar\n\t\tElectrical & Electronic Engineer\n************************************************************************************************\n************************************************************************************************\n***********************************************************************************************\/\n#include<avr\/io.h>\n#include<util\/delay.h>\n#include<avr\/interrupt.h>\n#include"dht11.h"\n#include"lcd.h"\nchar str[40],deg=223,hum=37;\nint main(void)\n{\nLCD_INIT(); \/\/LCD intilize\nLCD_write_string(1,1,"Temp and Humidity");\ntimer2_250ms();\ninit_dht11();\n_delay_ms(1000);\nwhile(1)\n{\n for(uint8_t i=0;i<8;i++)\n {\n humidity|=(sample[i]<<(7-i));\n temperature|=(sample[16+i]<<(7-i));\n }\n sprintf(str,"HR:%02d%c T:%02d%cC ",humidity,hum,temperature,deg);\n LCD_write_string(1,2,str);\n temperature=0;humidity=0;\n _delay_ms(1000); \/\/delay for LCD update\n}\nreturn 0;\n}\n<\/pre><\/div>\n\n\n