ESP8266 Community Forum

- Mon Jul 27, 2015 5:09 am #24365

tytower, do you know what the correct speed for a DH11 is? 15 doesnt make much difference

I don't it is trial and error at this stage . There is a default rate set in the code I think . You will have to look it up . There is also a thread with a few posts on DHT22 and speeds . If I find it I'll post back. From memory I tried from 6 to about 40 and settled on 15 as did someone else in that thread.

Thanks, I'll try lots of values and report what works best for a DHT11.. However looking at the code it indicates that he 3rd value is no longer used (ignored) as the code "works" out the best timing...

I will investigate later this evening

- Mon Jul 27, 2015 5:57 am #24368

However looking at the code it indicates that he 3rd value is no longer used (ignored) as the code "works" out the best timing...

It is not in Adafruits library I use

Code: Select all/* DHT library

MIT license
written by Adafruit Industries
*/

#include "DHT.h"

DHT::DHT(uint8_t pin, uint8_t type, uint8_t count) {
  _pin = pin;
  _type = type;
  _count = count;
  firstreading = true;
}

void DHT::begin(void) {
  // set up the pins!
  pinMode(_pin, INPUT);
  digitalWrite(_pin, HIGH);
  _lastreadtime = 0;
}


but I see its as you say in the GitHub version you are using which still says written by adafruit

Code: Select all/* DHT library

MIT license
written by Adafruit Industries
*/

#include "DHT.h"

DHT::DHT(uint8_t pin, uint8_t type, uint8_t count) {
  _pin = pin;
  _type = type;
  _firstreading = true;
  _bit = digitalPinToBitMask(pin);
  _port = digitalPinToPort(pin);
  _maxcycles = microsecondsToClockCycles(1000);  // 1 millisecond timeout for
                                                 // reading pulses from DHT sensor.
  // Note that count is now ignored as the DHT reading algorithm adjusts itself
  // basd on the speed of the processor.
}

Get you modules here:

https://www.banggood.com/custlink/KvGGhGF4wG

- Mon Jul 27, 2015 6:54 am #24372

OK. Im now stumped again...

For some reason I no longer get any readings.. and constantly get Failed to read from DHT Sensor in my code, not always but 80% of the time....

Code is trivial.. and Im now baffled again..
Ive set the 3rd param to 15.. baffling]

What board type are you using in the IDE when uploading the sketch ?

I had intermittent problems reading DHT11 on my 8266 201 running on a Dev board when I used the "Generic 8266" board setting. Changing to one of the esp-12 board settings when uploading the sketch resolved the issue.

- Mon Jul 27, 2015 7:16 am #24373 Just to make sure I download the same library, can you send me a link to the one you are using?

When I go to AdaFruit (https://learn.adafruit.com/dht/downloads) and click on the library it points me to the github repo..

Looking at Github, it appears this change occured from 1.0.0-1.1.0 ...

which version do u have?