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Mini Pearl Logger

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The Mini Pearl Logger is a powerful and inexpensive device for logging environmental data. It is based on an Arduino Pro Mini in combination with a real time clock and a microSD card reader. Soldering together these three common electronic components allows logging data from multiple sensors for multiple months. Some clever modifications of the components reduces the sleeping current between logging events and allows the logger to collect data unattended on small batteries (3 AAA) for two or more months. The total cost of parts for the Mini Pearl Logger can be under $15.00.

The DS3231 real time clock has an integrated temperature sensor and timekeeping is automatically corrected for temperature. Data from this sensor can be read and logged. The Mini Pearl Logger does not have any other sensors, but a wide variety of sensors (including I²C, 1 Wire, and Grove) can be used.

MiniPearl_20170606-9521ps.jpg
Above: These parts can be assembled into a data logger which will operate autonomously for months. The three blue PCBs are (left to right) 3 volt microSD socket, Arduino Pro Mini, DS3231 real time clock. Total cost can be under $15.00 if components are purchased carefully on eBay.

This logger is based on Ed Mallon's Cave Pearl Logger which uses a similar combination of components. Ed has done extensive testing to extend the field longevity to more than a year. We are still trying to replicate Ed's results, and have not yet managed to log data for more than two months on a few AAA batteries.

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Above: An assembled Mini Pearl Logger. Clockwise from upper right: battery case (e.g., 3 AA), microSD card socket, DS3231 real time clock, Arduino Pro Mini.

Parts

3 Primary components:

Also required:

  • Battery or battery case for AA or AAA. The Mini Pearl logger is a 3 volt device. Three alkaline batteries (3 x 1.5v = 4.5v) are adequate or four NiMH (4 x 1.2v = 4.8v). LiPo or LiPoly batteries (3.7v) are also good.
  • MicroSD card. Cards of 1 GB or smaller capacity are best because they tend to sleep better and at lower current. 128MB cards can allow 2 to 4 million data logging events, so larger cards are not needed.
  • CR2032 coin cell battery for real time clock.

Kits with all the parts needed to solder together a Mini Pearl Logger are available at the KAPtery for $19.00.

Assembly

There are two documents with guidance about assembling and getting started with the Mini Pearl Logger at the KAPtery Guides page.

Software

An Arduino sketch which logs data from the integrated temperature sensor and displays some of it on a serial monitor can be downloaded at the KAPtery Guides page.

Below are some research notes about activities done with the Mini Pearl Logger. Some of these notes include the sketch which was used in the activity described.

Activities

Purpose Category Status Author Time Difficulty Replications
Installing the water-level monitor - - @cfastie - - 0 replications: Try it »
Who will win in a world of...LASER DEPTHS? - - @cfastie - - 0 replications: Try it »
Willow Creek Water Quality Monitoring (EC and TDS) - - @MadTinker - - 0 replications: Try it »
The Mini Pearl Logger - - @cfastie - - 1 replications: Try it »
DFRobot TDS sensor first look - - @cfastie - - 0 replications: Try it »
Assembling a Mini Pearl Pro Logger - - @cfastie - - 0 replications: Try it »
Mini Pearl Jam - - @cfastie - - 0 replications: Try it »
New data loggers for long-term logging - - @cfastie - - 0 replications: Try it »
How to make a low power timer - - @cfastie - - 0 replications: Try it »
Mounting and deploying a Mini Pearl Logger - - @cfastie - - 0 replications: Try it »
Mini Pearl Logger longer - - @cfastie - - 0 replications: Try it »
Log all the data with Adafruit's TPL5110 Low Power Timer - - @cfastie - - 0 replications: Try it »
Longer Mini Pearl logging - - @cfastie - - 0 replications: Try it »

Activities should include a materials list, costs and a step-by-step guide to construction with photos. Learn what makes a good activity here.

Questions