• Welcome

    Welcome

    This blog has been created to share the knowledge of wireless sensor networks built at Stroud Water Research Center as part of the Christina River Basin Critical Zone Observatory.

    The Christina River Basin Critical Zone Observatory (CRB-CZO) is one of six projects across the country that together compose a huge multiyear, interdisciplinary effort funded by the National Science Foundation. Read more

  • Building the Networks

    Building the Networks

    Datalogger nodes consist of a microprocessor board paired with a radio module, all mounted in a weatherproof enclosure along with a solar panel and rechargeable battery.

    The nodes conserve battery power by sleeping most of the time, then waking periodically to take measurements from the sensors, and then transmitting their data through the mesh back to the base before going back to sleep.

    In areas with no mesh network, standalone loggers with just a memory card can be used.

  • Open-Source Hardware

    Open-Source Hardware

    We believe that using open-source electronics hardware for watershed instrumentation will transform our ability to deploy sensors, field instruments, and other electronic “eyes and ears” to unprecedented levels.

    High quality commercial sensors are relatively inexpensive and widely available. Easy customization of the Arduino node interface hardware and software means virtually any sensor can be used.

Getting sensor wires into the enclosure

One of the biggest challenges when building your own environmental monitoring instrumentation is how to get the sensor cable into the waterproof box with the logger.  There are several different methods, but I prefer plastic or nylon cable glands.  You can get them from a variety of vendors and for many different diameters of cables.  They also make ones that allow you to run anywhere from 2 to 6 or more wires into one gland, but those are  more complicated to use.  In most cases, just the single-cable ones will work.  You can get them from most industrial suppliers and electronics companies, but even Amazon has some like these for medium cables, and these for small cables.  One thing to keep in mind is the amount of threading on the gland.  If your enclosure isn’t too thick, most cable glands will work.  But if you’re mounting them on a box that has thick walls, you might need to buy glands with longer threads.  To drill your enclosure, I find that step drill bits work best.  Just be sure not to remove too much material, otherwise the gland won’t seal properly against the enclosure and you’ll get leaks.

Datalogger enclosures

One of the most important things to consider when deploying devices outdoors is what type of enclosure you’re going to use.  Many designers say they focus on finding the ideal enclosure first, then they design their circuit board to fit that particular enclosure.   For our projects, we have been using Pelican brand waterproof cases.   A handy size is their model 1050.   I like them for a couple of reasons:  they are available in a variety of sizes, and they are vented.   The waterproof vent allows the air inside the box to equilibrate with the outside air pressure.  This is extremely important when we are using vented pressure transducers because we can simply terminate the sensor’s vent tube inside the enclosure with some dessicant.  Without a vented box, the transducers would not give accurate water level readings.  Pelican cases are one of the few brands of cases in a convenient size that have a waterproof vent.

The clear cases are handy because you can place a solar panel inside the box to charge your batteries.  The only problem is that on sunny days the clear boxes tend to act like little greenhouses.  We have measured temperatures over 60 degrees C inside the cases on summer days, which is not very healthy for the batteries and some of the electronics.  So depending on your climate and how sensitive the contents of your box are to heat, you might not want to use a clear box for certain deployments.

For a cheaper, non-vented alternative to Pelican cases,  I have had good luck with Seahorse Cases.  These cases, along with the larger version of Pelican cases, have tabs that allow you to padlock the lid to keep people from tampering with the contents of the case.  The small micro cases like the one I linked above do not have locking tabs.