CODEWITHSUNDEEP
serial-porthexdriverlabview
Gary Z
Gary Z

Reputation: 87

Writing a Driver for an Extech HD300 Anemometer

I started a thread in the NI support forums about my project, but my current problem is more broad than just driver writing in labview. I have an anemometer that uses a USB UART bridge to interface with the computer. I asked Extech for any kind of documentation for and received only the communication protocol below.

Serial Communication Protocol

I encountered several problems working with this, so I took the software included with the anemometer and used portmon to sniff the commands going to and from, and here's where it gets worse. To simplify matters as best as I could, I only took ambient temperature readings. The following was what portmon captured when I used the manufacture's software to connect to the instument:

(This is the 'upload protocol' on the above protocol documentation)

AA 61 64 6A 67 08 40 00 40 00 01 00 00 C6 41 00 00 00 00 00 3C 1C C6 9A 19 99 42 00 3C 1C C6 00 00
AA 61 64 6A 67 08 40 10 40 00 01 7D 0C C6 41 00 00 00 00 00 3C 1C C6 39 1F 99 42 00 3C 1C C6 00 00
AA 61 64 6A 67 08 40 10 40 00 01 00 00 C6 41 00 00 00 00 00 3C 1C C6 9A 19 99 42 00 3C 1C C6 00 00
AA 61 64 6A 67 08 40 10 40 00 01 83 F3 C5 41 00 00 00 00 00 3C 1C C6 FB 13 99 42 00 3C 1C C6 00 00

This is slightly truncated, but the important parts should be there. The ambient temperature read about 76.5F at the time. So according to the documentation, this should be in the 10-13th bits, so I believe:

0000c641
7d0cc641
0000c641
83f3c541

To be the recorded ambient temperatures, but I have no idea how to read this. I see no reason why a conversion from Kelvin or Celsius would be necessary as there seems to be a bit for that in F1. Also of note is the fact that I get values completely different than anything documented for several fields, so either I'm reading something wrong or the documentation is just wrong. I haven't been able to get any more answers from the manufacturer about the protocol, so I have no idea why my data only half resembles what is expected.

Upvotes: 1

Views: 657

Answers (1)

J...
J...

Reputation: 31393

41C60000 converts to 24.75 as an IEEE754 standard 32-bit single precision float. This looks like a Celsius value which would map to 76.55 F.

For the rest of the data you would have :

 41C60000 = 24.7500000000000000000 
 41C60C7D = 24.7560977935791015625 
 41C5F383 = 24.7439022064208984375

I think that sorts out the endianness and formatting for you.

Upvotes: 2

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