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Hyrdos 21 Gen2 – Can’t Change Address

Home Forums Environmental Sensors Hyrdos 21 Gen2 – Can’t Change Address

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    • #17778

        I have some new METER Hydros 21 (gen 2) sensors and I want to hook them up to my Mayfly to calibrate them against some known standards before I deploy them.  The problem is that the b_address_change sketch (https://envirodiy.github.io/Arduino-SDI-12/b_address_change_8ino-example.html#xample_b_page) can’t seem to determine what address the sensor is currently on out of the box so I can’t set it to something new.  It just keeps cycling through all the available addresses and says they are all vacant.  I have to quit the serial monitor in VSC to get it to calm down.

        So far, I’ve tried:

        • changing which data port the sketch is looking for
        • updating to the latest version of Modular Sensors
        • multiple sensors (to see if one was just faulty)

        The sketch worked on a different gen 2 Hydros 21 that I calibrated in January.  Is there a new version of the address change sketch that I should be using now?

        Any ideas or things to try would be welcome.


      • #17779
        Shannon Hicks

          Does the sensor have bare wires or a 3.5mm stereo plug?  Either way, ensure that the sensor is connected properly to the Mayfly with the sensor power wire going to a 3.3v or 5v constantly powered pin during the address changing sketch.  And make sure that the data wire of the sensor is connected to the proper Mayfly pin, which is usually D7 in the examples we write.  And of course the sensor ground wire must be connected to a Mayfly GND pin.  If you’re using a Mayfly Grove jack, it’s best to use either of the 2 jacks labeled SDI-12, and make sure the header jumper block next to the Grove jack is set to 3v or 5v.

          Also make sure that you’re using the latest ModularSensors library files on your computer when you compile and upload the sketch.  Changes to the Hydros 21 sensor last year require a slight timing adjustment in one of the library files (line 107 in MeterHydros21.h).  You can read more details about it here:  https://www.envirodiy.org/topic/hydros-21-decagon-ctd-reading-error/#post-17066

        • #17782

            Thanks, Shannon.

            I did double check the things you mentioned.  And as I said, this whole setup just worked when I did it with different gen 2 Hydros sensors in January.  Still not having any luck.

            Are there other things to try?

          • #17788
            Shannon Hicks

              If you’re able to swap out a Hydros21 manufactured in 2022 with your hardware and everything works fine, but sensors from 2023 aren’t working, then it’s possible that they’ve made another design change that requires some tweaking of the ModularSensors code library to make them work correctly.  We’ve had a report of one other person having trouble communicating with a brand new Hydros21 that was just purchased, so I’ll have to follow up with Meter Group to see if there’s something we should know.

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