Data Logging
 

Well, I will break the ice...

Although it was mentioned elsewhere in Ecorenovator, I think this is a good place to do a user report...

I purchased a data logger called The Arduino Logger, from a local guy for $35 bucks.


All you gotta do is give it some power and a SD card, turn it on and it starts logging data. It just doesn't get any simpler or cheaper than that.

It has a 1-wire pin header that will allow you to string up to 128 different 1-wire devices. One 1-wire temperature sensor device is mounted on board and currently that's all I am using, so I'm getting my money's worth right out of the box.

I initially made a power supply from a 3-cell cordless phone battery pack, but it didn't supply enough voltage for the device to cycle correctly. Once I got a 4-cell battery box from a local electronics store, the action started happening. It ran well on this supply for about 10 hours, then the cells were drained too low.

Then I made a power supply from a cell-phone power supply which I got at Goodwill for $1.99, and have been running the data logger ever since without problem.

The Arduino Logger has a real-time clock which can be set through the serial port.

The maximum SD card is 'bigger than 32 GBytes'. I did a sample run, measured the size of the file and calculated that a 32 GB SD card could hold somewhat less than 1,735 years of data, using one sensor. Of course, using more sensors would reduce this. Using a full 128 devices would reduce the maximum time to 13.6 years, still not too bad.

I have been accessing the files by removing the SD card, plugging it into my computer, and downloding the files to my computer. It is also possible to access data through the serial port, but I haven't tried that yet.

Here's the beginning of a data file:


As you can see, each read (default = 1 minute) has a date, time, data, "periodic" in each reading cycle.

Once I get the files into the computer, I use a text editor (I use Textpad) to strip out the parts I don't want, then I import the data into a spreadsheet (I use Gnumeric) for post-processing and graphing.

This device comes with source code if you want to modify the firmware, eagle files if you want to build your own board, and I didn't even mention that there are an additional 6 analog ports and about 8 digital ports that can be configured in various ways.

There are other data loggers that have a much more developed and easier to user interface, but I haven't come across anything with nearly the power, flexibility and low cost.

The version in the photo (which I have) is available, as is a half-sized version of the board with surface mount components that has the same functionality.

Travis is working on a new rev which will have USB rather than serial, and other improvements.

-Jim