DHT 11 Sensor and NI USB-6009

[Sleepar]

Hi all,

I am a new user to LabView with only a CLAD certification so please forgive my ignorance on the subject matter at hand.  I am attempting to use a DHT 11 Temperature and Humidity sensor (Factsheet: http://www.micro4you.com/files/sensor/DHT11.pdf ) with a NI USB-6008.   I have not had any luck on finding information on this combination for data collection and have began to wonder is it even possible. 

I do know that the DHT sensor outputs digital signal and that typically it is used with an Arduino board but I need to use it with my DAQ. 

• Can anyone give me a general run down on whether or not this is possible?

• If so, what needs to be done to allow the DAQ and sensor to communicate?

• And if it is not possible, any information on why that is and suggestions on what I can do to integrate temperature data into my LabView code using the USB-6009?

I apologize for the broad nature of my question, I'm just looking for basic general knowledge on the subject so I have a foothold for attacking my problem at hand.

Thank you,

Sleepar

[johnsold · Accepted solution]

Sleepar,

You will not be able to use that sensor with the USB-6008.  Although it is a rather poorly written specifications document, it is clear that some of the timing is mcuh faster than you can achieve with the software timed digital inputs and outputs of the USB-6008.  With the USB-6008 you need to think in terms of tens of milliseconds minimum timing on digital lines and allow considerable jitter at those rates.  Anythign with microsecond timing is out of the question.

Probably the easiest way to get temperature data to a USB-6008 is to use a semiconductor temperature sensor such as an LM35 and an analog input to the DAQ.

If you need to use the DHT 11, you will need some external circuits to capture the five bytes of data and present them in a format the USB-6008 could handle.

Lynn

[SnowMule]

You might be able to make it work on an analog input, then look at that waveform on the computer.  The 6008 will sample at 1khz... while not "fast", it may be enough to see what you're looking for.

A quick glance at the DHT22 datasheet didn't show much in the way of actual frequency/timing...

[johnsold]

The timing spec (lack thereof) was the source of my comment about the quality of the documentation.

It does apear to require a "command" signal on a digital output line to get a response.  It is not clear what the timing requirements are there and whether the 6008 could satisfy them.

Lynn