Wednesday, October 26, 2011

I get letters

None about the rocketometer, as no one else has one (I don't even have one yet...) but about Logomatic Kwan. After publishing the thing in 2009 (has it really been that long?) I got letters from two people in two weeks.

First, I got one from a researcher at the University of Washington. His letter goes like this:

First, thank you for publishing your firmware. I am just starting a project where I will be making a custom datalogger that will monitor various forces inside of a prosthetic socket as well as keep an inventory of socks the user is wearing. However, before I can start on the final product, I need data to get some funding. That is where the logomatic comes in, I am using that combined with a CAEN RFID board to collect the data I need. The CAEN communicates with the logomatic through the UART0 interface. 

I am using the following command line to obtain the inventory data from the CAEN device: "H 1 0 8001000000005358002100000008000100130000000F00FB536F757263655F3000"

In the "LOK" file, I see where it prints out that line but the data is corrupted and there consistently an extra 16 bytes of data after. Here is a sample from the LOK file: "€    SX !     ├╗Source_0 4 8406 3540 2879"

So now you hopefully understand the background and I can ask my two questions. From your write-up, the data from the command line is printed in the log file, why is what is logged different from what is in the command file (e.g. 0x0 is converted to 0x20)? Second, is the extra 16 bytes at the end of the line received data?

I appreciate you getting back to me so quickly and look forward to hearing back from you. 


David S****
University of Washington, Mechanical Engineering
This guy has a specific problem, he has told me what he has done, and is appropriately respectful and/or polite. After some conversation, I was able to solve his problem.

The converse is this:


I have a logmatic v2 datalogger. I want to sample 2 pins. 1 pin for a pulse anemometer. The other pin voltage to sample a weathervane. And add the RTC value.
Can you help me?

This one for whatever reason rubbed me wrong. It almost struck me as asking for me to do his homework. There is no evidence that this guy has done anything on his own yet, or even that he has Logomatic Kwan. It is out of the blue, with no introduction or any idea how he found me (David S. didn't either, but the other factors outweighed that).
I probably can help him. The only reason I bring this up is that this might be an interesting problem. I actually deleted his message without answering it, just because it bugged me. But, I pulled it out and responded.
The first hit for "pulse anemometer" is here. This anemometer produces a ~50% square wave, one pulse for every 1m or so of wind travel. If the signal is 1Hz, then you end up with 1m/s of wind speed. Depending on if there is any bounce on the signal, it could be plugged into the PPS channel (SCK on the Logomatic) to get microsecond precision on the signal. If the signal is too bouncy, it would need to be sampled at a high rate, but that's what the Logomatic is for. It would produce vast amounts of data to be post-processed, but that's ok.

The letter is even less specific about the weathervane. I suppose it is analog, perhaps a sin/cos signal. The same manufacturers as above make a weathervane based on a 1000 ohm potentiometer, so voltage is proportional to angle from North. That is straightforward analog, and would be fine sampled at 10Hz.

If he runs the system in NMEA mode, he will get $PKWNL packets with the RTC he wants once every second.

So, I can help him, but he still needs to do quite a bit of work.

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