DHT11 Sensor Interfacing With ATmega16

DHT11 Sensor Interfacing with ATmega16 / 32. DHT11 is a single wire digital humidity and temerature sensor! which gi"es relati"e humidity in ercentage and temerature in degree #elsius.

Introduction •

DHT11 is a single wire digital humidity and temerature sensor! which ro"ides humidity and temerature "alues serially.

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DHT11 sensor ro"ides humidity "alue in ercentage in relati"e humidity $2% to &%' (H) and temerature "alues in degree #elsius $% to *% +#)

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DHT11 sensor uses resisti"e humidity measurement comonent! and ,T# temerature measurement comonent.

Pin Description: •

DHT11 is - in sensor! these ins are ##! DATA! ,D and one in is not in use! shown in fig 0elow.

Fig) Pin diagram of DHT11

Pin No.

Pin Name

Pin Description

ower suly 1

 ## 3.3 to *.* olt D#

2

DATA

Digital outut in

Pin No.

Pin Name

Pin Description

3

,#

,ot in use

-

nd

round

 Communication with microcontroller

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DHT11 uses only one line for communication. The "oltage le"els with certain time "alue defines the logic one or logic ero on this in. The communication rocess is di"ided in three stes! first is to send reuest to DHT11 sensor then sensor will send resonse ulse and then it starts sending data of total -%  0its to the microcontroller.

Fig) Communication process Start pulse (e!uest)

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To start communication with DHT11! first we ha"e to send the start ulse to the DHT11 sensor.

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To ro"ide start ulse! ull down the data in minimum 14ms and then ull u! as shown in diag.

esponse

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After getting start ulse from the controller! DHT11 sends the resonse ulse to the microcontroller which will indicate that DHT11 recei"ed start ulse.

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The resonse ulse is low for *-us and then goes high for 4%us.

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After sending the resonse ulse! DHT11 sensor sends the data! which contains humidity and temerature "alue along with chec5sum.

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The data frame is of total -% 0its long! it contains * segments $0yte) and each segment is 40it long.

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In this * segments first two segments content humidity "alue in decimal integer form. This alue gi"es us (elati"e ercentage Humidity. 1st 40its are integer art and ne7t 4 0its are fractional art

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 ,e7t two segment content temerature "alue in decimal integer form. This "alue gi"es us temerature in #elsius form.

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8ast segment is the chec5 sum which holds chec5 sum of first four segment.

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Here chec5sum 0yte is direct addition of humidity and temerature "alue. And we can "erify it in microcontroller whether it is same as chec5sum "alue or not. If it is not eual! then there is some error in the data "alue otherwise the data is correct.

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9nce microcontroller recei"es data! DHT11 in goes in low ower consumtion mode until the microcontroller do not sends start ulse again. "nd of frame

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After sending -%0it data! DHT11 sensor sends *-us low le"el and then goes high. After this DHT11 goes in slee mode.

Circuit diagram

Fig) Circuit diagram •

The a0o"e circuit diagram shows interfacing of ATmega16 / 32 to DHT11 sensor.

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In that! 8#D is interfaced to 9(T: in -0it mode! and DHT11 sensor is connected to D6 $in no 2%).

Programming of DHT11 •

;irst initialie the 8#D1672<-0it li0rary.

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Define in no. to interface DHT11 sensor! in our rogram we define D6 $in no. 2%).

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Send the start ulse to DHT11 sensor! ma5ing low to high.

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(ecei"e the resonse ulse from the DHT11 sensor.

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After recei"ing the resonse! recei"e -%0it data serially from DHT11 sensor.

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Dislay these recei"ed data on 8#D1672 along with error indication.

/*  * ATmega16_DHT11_Project_File.c  *  * http://www.electronicwings.com  */ #incl!e "ar/io.h$ #incl!e "st!li%.h$ #incl!e "st!io.h$ #incl!e &'(D16)_+%it.h& #!e,ine DHT11_P- 6 int_t c02-_3H2D_3H2-_Temp2D_Temp2(hec45m oi! 3e7est89 /* icrocontroller sen! start plse or re7est */ ; DD3D <0 81""DHT11_P-9 P=3TD >0 ?81""DHT11_P-9 /* set to low pin */ _!ela@_ms89 /* wait ,or ms */ P=3TD <0 81""DHT11_P-9 /* set to high pin */  oi! 3esponse89 /* receie response ,rom DHT11 */ ; DD3D >0 ?81""DHT11_P-9 while8P-D > 81""DHT11_P-99 while88P-D > 81""DHT11_P-99009 while8P-D > 81""DHT11_P-99  int_t 3eceie_!ata89 /* receie !ata */ ; ,or 8int 70 7" 7BB9 ; while88P-D > 81""DHT11_P-99 00 9 /* chec4 receie! %it  or 1 */ _!ela@_s8C9 i,8P-D > 81""DHT11_P-99 /* i, high plse is greater than Cms */ c 0 8c""19<8)19 /* then its logic H-H */ else /* otherwise its logic '=E */ c 0 8c""19 while8P-D > 81""DHT11_P-99  retrn c  int main8oi!9 ; char !ataG lc!init89 lc!_clear89 lc!_goto)@829 lc!_print8&Hmi!it@ 0&9 lc!_goto)@8219 lc!_print8&Temp 0 &9  

/* initialiIe '(D */ /* clear '(D */ /* enter colmn an! row position */

while819 ; 3e7est89 3esponse89 -_3H03eceie_!ata89 D_3H03eceie_!ata89 -_Temp03eceie_!ata89 D_Temp03eceie_!ata89 (hec45m03eceie_!ata89

/* sen! start plse */ /* receie response */ /* store ,irst eight %it in -_3H */ /* store ne)t eight %it in D_3H */ /* store ne)t eight %it in -_Temp */ /* store ne)t eight %it in D_Temp */ /* store ne)t eight %it in (hec45m */

i, 88-_3H B D_3H B -_Temp B D_Temp9 J0 (hec45m9 ; lc!_goto)@829 lc!_print8&Krror&9  else ; itoa8-_3H2!ata219 lc!_goto)@81129 lc!_print8!ata9

lc!_print8&.&9 itoa8D_3H2!ata219 lc!_print8!ata9 lc!_print8&L&9 itoa8-_Temp2!ata219 lc!_goto)@86219 lc!_print8!ata9 lc!_print8&.&9 itoa8D_Temp2!ata219 lc!_print8!ata9 lc!!ata8)DF9 lc!_print8&( &9 itoa8(hec45m2!ata219 lc!_print8!ata9 lc!_print8& &9  _!ela@_ms819  