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Author Topic: A really inexpensive data logger with only three components.  (Read 791 times)
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I am currently working on a DIY underwater flow sensor using an Arduino based data logger. I hope to turn the units into a robust open source platform for many different types of research.
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It seems like most on of the folks on this list already know more than I do about building data loggers,  so please forgive me if this amounts to spamming the thread.  But I wanted to post a link to a really inexpensive data logger I have come up with for one of my projects, based on a 3.3v Pro Mini and a cheap DS3231 breakout board from eBay.

http://edwardmallon.wordpress.com/2014/07/01/a-10-diy-data-logger-is-born/

I have put a few of these together now, and they all seem to be running well, with the only caveat being that the voltage regulator on the pro mini draws about 1.5mA while the unit is sleeping.  So not great for long term deployments, but good enough for the bench-top prototypes I have used them for thus far.  Also, all the usual caveats apply regarding the reliability (drift, etc) of those knock-off RTC's.  Rest assured that I use more reliable clocks for actual fieldwork.  Still, you can put one of these things together for about $10-$20 depending on how cheap you want to go on the parts, and that's handy when you are just trying out a new sensor.




* A3ComponentDIYDatalogger_640pix_v5-01.jpg (209.07 KB, 640x594 - viewed 54 times.)
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Don't worry. There's always a first time for all of us smiley

Your solution looks great.

To solve your extra current draw you have to feed the 328 directly and not through the voltage regulator.
 
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I am currently working on a DIY underwater flow sensor using an Arduino based data logger. I hope to turn the units into a robust open source platform for many different types of research.
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I know the new Pro Mini boards have a jumper that lets you disconnect the voltage regulator very easily. But I am using TinyDuinos for my long term deployments because although their mcu board is unregulated, they have regulators distributed to their shields, so the SD card, etc. still gets a steady 3.3v even though the Vbatt varies widely over time.  Their physical profile is compact, and when bolted down is pretty resistant to knocking around, which for me is an issue.

But this little ProMini logger should still go at least a couple of months on 3x AA's and that's probably Ok for alot of people.  I have also been looking at the Ultra's from Rocket Scream, as their voltage regulator has a much lower quiescent current than the sparkfun board.  I will get around to testing them out eventually.
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I am currently working on a DIY underwater flow sensor using an Arduino based data logger. I hope to turn the units into a robust open source platform for many different types of research.
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That reminds me about another question I have been meaning to post to the playground, regarding sleeping & data loggers

There are lots of code examples out there where people use the power.h library to shut down peripherals  (SPI, TWI, etc) during sleep mode to save power, but I have yet to find an example that has devices connected to those peripherals both before and after the sleep cycle.

If I do something like this to save power:

power_twi_disable();
power_spi_disable();
....sleep....
power_twi_enable();
power_spi_enable();

When I have both an SD card, and several sensors connected to the I2C lines (with ext 4.7k pullups) - what happens to those external devices?  
Do those connected sensors get confused when the Arduino peripherals stop?
Do I then have to re-initialize them all again like I did in the setup after enabling  I2C and SPI?

If so there might be no net power savings for shutting down the peripherals, because many of the sensors (and the Sandisk sd card) draw very little power when sleeping, but take a significant amount of time & power to initialize...

I would appreciate advice from anyone who has experience with this...  

(..also wondering if shutting down a peripheral on the mcu, but having a real device connected to the wires, creates some kind of unexpected current drains, etc, pins floating? or something else like that?)

P.S. I was not planning to shut off the BOD...It seems like a handy thing to have on battery powered loggers.
« Last Edit: July 17, 2014, 05:07:26 pm by EKMallon » Logged

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