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Hydros 21/Decagon CTD: reading error

Home Forums Environmental Sensors Hydros 21/Decagon CTD: reading error

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    • #14387

      This being our first year implementing our EnviroDIY unit, we are trying to keep it simple and are only using one sensor: the Hydros 21 (which, if I am not mistaken, is also known as the Decagon CTD).  Since it is so simple, compared to other units, I am slightly embarrassed to admit that I cannot seem to get any readings from the sensor.  Each time it returns the error reading of -9999.0.  I had this happen with some of the sensors used in learnEnviroDIY (e.g. the DS18B20) but after some fiddling with the connection I got it to return data successfully.  With the Hydros, I have quickly run out of ideas of ways to fiddle around with it.

      Here are my details:

      • I am using the code from the DRWI_LTE example because it used the Hydros 21. I removed all of the parts relating to the Campbell turbidity meter.  The code can be found here: https://github.com/EnviroDIY/ModularSensors/blob/master/examples/DRWI_LTE/DRWI_LTE.ino
      • My hardware has the XBee connection and battery but I do not have my solar up and running yet.  My last battery reading was 4.882 volts.  MY hydros 21 has the 3.5mm stero plug and is connected to pin 7.  See attached pictures of my setup.
      • Snippet jpeg images of the code script and output are also attached.  While not in the photos, I will mention that I made sure to check that my variable list and UUID are in the correct order.  Everything is uploading to MMW successfully.

      Any ideas?

    • #14392
      Sara Damiano

      Are you sure you’re SDI-12 address is set correctly?  You can use this program to check/change it:  https://github.com/EnviroDIY/ModularSensors/blob/master/tools/sdi12_address_change/sdi12_address_change.ino

    • #14393
      Shannon Hicks

      As Sara suggested, the issue is probably related to the SDI-12 address of the sensor. Meter Group ships all of their sensors with a default SDI-12 address of “0” (zero). They do this because it’s the channel their sensors need to be programmed to for working with their own brand of dataloggers. But Meter group sensors don’t respond to SDI-12 commands unless they are programmed to anything other than 0. The DRWI_LTE example sketch you’re using is looking for the sensor on channel 1, so the easiest thing is to use the address changing sketch Sara linked to change the sensor channel to 1. Then reprogram your Mayfly with the logging sketch and it should work.

    • #14394

      It worked! Thank you, thank you!  I very much appreciate all the help.

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