[Danny Waz]

Update 3: Looks like EnviroDIY has merged my backward-compatible slave-side additions into their main library, so you don’t need my fork if you have the latest version. See example “g” for a slave implementation.

[Danny Waz]

The code is publicly available in my GitHub (link). For it to work, you will need my fork of the EnviroDIY SDI-12 library in your Arduino/libraries folder. At the time of this comment, it is ahead of EnviroDIY:master and fully backward-compatible, so it will not break your old sketches if you are already using that library.

[Danny Waz]

@shicks I assume you have been busy and this hasn’t happened yet… I’d like to start playing around with the GPRSbee on my own. Any recommendation on which Rev to buy and where to buy it?

[Danny Waz]

Update 2: I have posted the modified library and an example implementation sketch in a fork off of the EnviroDIY Arduino-SDI-12 repository.

https://github.com/dwasielewski/Arduino-SDI-12

[Danny Waz]

Pardon the somewhat off-topic response, but regarding reading serial data I have found this post extremely helpful. Both of the examples above hold the loop() hostage until the whole string comes in. That’s okay in a small, single-sensor sketch, but it is susceptible to (a) truncating the string if the arduino gets ahead of the incoming data and (b) getting hung in the serial.read() “while” loop. It’s more robust (although, admittedly, more complicated) to add a single byte per loop() iteration.

[Danny Waz]

According to the datasheet, the “RS232” models MB736x are 0-Vcc (typical RS232 is -13V to +13V). Of course, it will be inverted from TTL, but if you account for that in your softwareSerial constructor, I do not see why you should need an external converter (MAX232 or similar). In fact, the converter might cause problems if it’s shifting the logic levels on the sensor side. Disclaimer: I haven’t done this myself; I’ve only used the true-TTL MB7389 and the I2C versions. Feel free to correct me if you have experience with it.

On the subject of sensor selection for future reference, the 7369/7389 might be preferable for water surface detection because they report the “largest” return rather than the “nearest” return. I can attest that the MB7389 does a good job of ignoring small objects partially obstructing its field of view. If the sensor field of view is relatively clear it’s probably a non-issue.

[Danny Waz]

Thanks, @shicks. I will look into those too. I am glad to hear you are planning a tutorial already.

[Danny Waz]

Thanks for the links. Of these, the NimbeLink Skywire looks most like what I was imagining. The FONA boards have some promise, but the Adafruit library does not support data yet for the linked 3G version. I would consider a cell modem like the Raven a good option for a remote system based on a full-fledged computer (say, an RPi or NUC), but it looks like it would require a middleman to interface with a light MCU like an Arduino/Mayfly. Still good info to file away for future projects!

By the way, if you end up going with a CR300, Campbell makes their own compatible cellular modems (COM110A). I don’t about the prices, but staying within one company’s ecosystem might simplify the setup.

[Danny Waz]

I should mention that when I was about 90% done with it, I discovered Vegetronix offers something similar off-the-shelf. However, I am benefiting from some advantages to my approach:
1. It is customizable, which is especially useful for integration into custom applications on the host PC
2. Total cost was ~$15

[Danny Waz]

You are not missing something. It would be more accurate to say “ultrasonic stage height sensors”, because depth is merely retrieved, not sensed. This is problematic when one cannot easily survey the sensor as you said, even more problematic for sensing streams with moving beds. Presently, something like a pressure transducer can measure depth in-situ, but non-contact methods almost universally require an a priori stage-depth relationship. In the early 2000s, the USGS (John Costa, Kurt Spicer, et. al.)showed it’s possible to measure depth with ground-penetrating radar, but that’s not exactly economical or practical.

One of my current projects is tacking exactly that problem. It’s not ready for prime time yet, but if you are working on similar technology and wish to collaborate, feel free to private message me.

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