DHT11 Temp/Humidity sensor

Gary Wilkerson

Has anyone interfaced to this sensor? I'm having problems reading the 40 bit stream. Any examples would be appreciated.

Gary

PJAllen

Looks like this is big with the arduina crowd.
Details are sketchy. Found a datasheet of sorts and a page with arduina code.
It's "9600", but I don't know if their convention is 'True' or 'Inverted'.
Are you using a BS2 of some sort?

Kirk Fraser

You can find related advice near the bottom of this page on Earth Measurements.
http://www.emesystems.com/BS2index.htm

Gary Wilkerson

PJ and Kirk,

Sorry for the delay responding; I had to make an unexpected trip to Chicago. It is big with the Arduina crowd, I was attracted to the price. I am using a BS2. I think the problem I'm having is parsing the string.

I'll take a look at the emesystems link.

Thanks!
Gary

JAGO

Hi Gary,

I hope you are ok, i have the same problem with the DHT11 sensor, i try to connect to the basic stamp 2, but i can't... i would like to know if you solve the problem or not??? i'm continue trying with the sensor if i have good news... i'll notify you.

Greetings

JAGO

This is the code of the sensor DHT11 for arduino.. it's writed in C, i try to traduce to PBASIC, if any have some idea to do this is welcome...

Best regards..

#define DHT11_PIN 0 // ADC0

byte read_dht11_dat()
{
byte i = 0;
byte result=0;
for(i=0; i< 8; i++){


while(!(PINC & _BV(DHT11_PIN))); // wait for 50us
delayMicroseconds(30);

if(PINC & _BV(DHT11_PIN))
result |=(1<<(7-i));
while((PINC & _BV(DHT11_PIN))); // wait '1' finish


}
return result;
}


void setup()
{
DDRC |= _BV(DHT11_PIN);
PORTC |= _BV(DHT11_PIN);

Serial.begin(19200);

Serial.println("Ready");
}

void loop()
{
byte dht11_dat[5];
byte dht11_in;
byte i;
// start condition
// 1. pull-down i/o pin from 18ms
PORTC &= ~_BV(DHT11_PIN);
delay(18);
PORTC |= _BV(DHT11_PIN);
delayMicroseconds(40);

DDRC &= ~_BV(DHT11_PIN);
delayMicroseconds(40);

dht11_in = PINC & _BV(DHT11_PIN);

if(dht11_in){
Serial.println("dht11 start condition 1 not met");
return;
}
delayMicroseconds(80);

dht11_in = PINC & _BV(DHT11_PIN);

if(!dht11_in){
Serial.println("dht11 start condition 2 not met");
return;
}
delayMicroseconds(80);
// now ready for data reception
for (i=0; i<5; i++)
dht11_dat = read_dht11_dat();

DDRC |= _BV(DHT11_PIN);
PORTC |= _BV(DHT11_PIN);

byte dht11_check_sum = dht11_dat[0]+dht11_dat[1]+dht11_dat[2]+dht11_dat[3];
// check check_sum
if(dht11_dat[4]!= dht11_check_sum)
{
Serial.println("DHT11 checksum error");
}

Serial.print("Current humdity = ");
Serial.print(dht11_dat[0], DEC);
Serial.print(".");
Serial.print(dht11_dat[1], DEC);
Serial.print("% ");
Serial.print("temperature = ");
Serial.print(dht11_dat[2], DEC);
Serial.print(".");
Serial.print(dht11_dat[3], DEC);
Serial.println("C ");

delay(2000);
}

PJAllen

Either of you DHT11 fans have a proper datasheet for it?

JAGO

Hi PJ,

this is the datasheet for this sensor..http://www.robotshop.com/PDF/dht11.pdf

thanks

PJAllen

Conceivably this could be done with PULSIN.

Each bit is preceded by a 50us low time with the following
high time determining the data_bit's value, a "0" is 26-28us and
a "1" is 70us.

I doubt that any Stamp is fast enough to
decide 0-or-1 (or 0-or-not0) on the fly.
You have to establish a VAR array, take in those times/transitions
and then interpret the results (later.)

A bit transmission always begins with the 50us (!!) low time - that's the
time you/it has to stash in RAM the PULSIN val result and get ready for
the next incoming data_bit/pulse_time.

I may be wrong, but a BS2sx or BS2px will be required for the speed
and the scratchpad RAM.
(It's very SX'able and Propeller easy.)

Post Edit -- If you don't take in the 8 error check bits at the end, then you cut your RAM requirements from 40bytes to 32. [It's a byte for the pulsin_time taken by each data_bit (40 or 32.)]

Gary Wilkerson

PJ,

I think you're right. I didn't consider the speed of the processor and it being unable to respond to/ detect the states.

Need to look further, thanks for the help.

Gary