Temperature and Humidity Sensor

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About: Disclaimer: The author is not responsible for loss of life, limb or property. The author is not responsible for your actions. The author is not responsible for anything. In fact, the author is completely i...

At work we use a lot of environmental monitors. I wanted something similar for home. I saw these DHT-11 Sensors on ebay pretty cheap. there are wider range and higher resolution version available but I wanted a few of them cheap.

I decided to do a simple serial interface so it would work easily with Linux, Pic's, Windows etc..

Step 1: Prototype

I had a bunch of PIC16F73's left over from a project so I used them.

I opened the serial to USB adapter's case and ran a wire from the USB power pin to pin 9 on the serial port. This is actually the ring indicator input but this way I didn't need an external power connector.

The hex file attached uses a simple menu interface good for testing and a raw data feed command for using in scripts.

Step 2: Final Design

I saw these nice time bulkhead boxes on Electronics Goldmine. I used them in my Instructables on Balun's too.

I used a mill to cut the holes for the serial port and sensor but a Dremel or drill and file will do just as well.

Step 3: Schematic and Code

I used a 10Mhz ceramic resonator instead of the 10MHz crystal and two 12pf caps. I just happened to have a bunch of those around and its quicker to wire on a protoboard

Step 4: Communicating With It

Its pretty simple to talk to. I use 2400 Baud to help with slow devices or long cable runs.

The screen shot above was from Zterm on a mac.

The commands are simple and can be upper or lower case:

V - Version (4 line info header)

A - Ascii Reading Output (2 lines in plain English)

T - Temperature Reading (always 3 digits)

H - Humidity Reading (always 3 digits)

B - Both Reading separated by a comma

all readings are zero padded for fixed length. This makes it easy to read with some languages. All lines are terminated by a CR and LF. If the sensor fails the English commands will say "Sensor not Responding" and the data reads (T-H-B) will return 3 dashes in place of the reading.

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