Water Probes with BNC Connectors

goldylamont

Hi, I would like to create a DAQ (data aquisition) of sorts to get water quality measurements from standard water probes with BNC Connectors. I know that these probes take a small amount of electricity and you can determine their reading depending on the voltage they return. I've included links below. Basically what I would like to do is use either the Basic Stamp or Propeller to constantly gather and log data such as pH, ORP and temperature from water using these probes. I would then like to somehow get this information to a web server where I can graph it. I can't find any information though on how to interface these probes to a computer--the probes use the common BNC connectors to interface. There are companies that sell DAQ devices however any one that I have seen with a BNC connector on it is close to or over $1000. I'm looking for any advice on how I could set up a system to continuously probe water quality and log these values; and also to then display this info via a LAMP/Unix type webserver. I'm thinking that if I can figure out how to get the info from the probes I could use a mini-computer like a Beagle Board to host the web server; however perhaps a Propeller could do this also? Or perhaps I simply use a Basic Stamp to get the data and then somehow send this to a computer for further analyses? Any advice on how you would design would be greatly appreciated.

link to probes I would like to use. They all have BNC style connectors
http://www.americanmarineusa.com/

link to Beagle Board mini-Unix computer: http://beagleboard.org/

thanks!

John R.

You'll need to attack this on a "per probe" basis. Depending on what's being measured, the probes have different requirements, and provide different readings. Compounding this, for some types of probes, there is not a "standard" output.

pH is one of the 'easier' ones to deal with in that the probe puts out a voltage, and this voltage is "standard" so you can use pH probes from about any source. You will need some op amps and calibration circuitry, but these are easily found on the web. Dr. Tracey Allen has a nice article and schematic on pH measurement on his web site.

I'm not totally up to speed on the other types of probes yet (but am also working on this type of thing). I can tell you that conductivity (or hardness) is a "Smile shoot", and probes from different manufacturers are not interchangeable. I this case, you also need to supply an AC current to the probe. Geometry, shape, and size of the probe will all affect your readings.

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John R.
Click here to see my Nomad Build Log

goldylamont

thanks for the info John! I searched using your suggestions and found some good info. the circuitry for this may be too involved for me--are there any prebuilt solutions available that will output raw data? my main focus would be on graphing/logging this information. I may still like to create the circuit from scratch but would be happy if there was a prebuilt starting point that I could build up from. (p.s. your "nomad build" robot looks really cool!)

John R.

The short answer is yes, but they (and especially a collection of them) can get expensive. In addition to your link at American Marine, you might want to check out the following:

* Omega
* Cole-Parmer

and other "laboratory" or "industrial control" suppliers.

There are also "off the shelf" units that will log one or more of these measurements that can be found in aquarium and/or hydroponics supply stores (brick and mortar or online).

Can I ask specifically what you're trying to measure/record? (aquarium, stream water, well water, etc.)

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John R.
Click here to see my Nomad Build Log

Tracy Allen

Goldylamont,

I referred you in PM to Vernier, for probes and amplifiers. Since this is a personal aquarium project, you might find the following video interesting, a robotic project that plunges one probe after another into the aquarium in order to avoid interference:
engineering.vernier.com/general/projects/aquarium/

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Tracy Allen
www.emesystems.com

goldylamont

Tracy, you found me! Thank you both John and Tracy; very helpful information. I wish my circuit board skills were like they were 10 years ago at Berkeley! but alas, i am just a lowly home hobbyist/consultant/musician now. I really do appreciate the suggestions and when I get some extra $$ i think i will follow through and try out one of the DAQs you recommended. What I'm realizing now is that I think my expertise and interest is more in developing a great web GUI and charting interface; more high level stuff now that I see the complexities of the DIY approach to water probing. I've probably spent 20-30 hours researching all of this and a friend of a friend told me to check out the Basic Stamp chip...from there i started salivating over the Propeller; but ya I would need to dust off those old engineering books to get up to speed. i dunno, maybe there's a circuit maker out there that would want a nice UI on top of their project. In any case I appreciate all the help. wish me luck!

bdickens

I've had a project to do much of this on and off. (More off than on) and I agree with the various postings. Simple = Expensive, complex = Less expensive. None of them were easy. We are measuring water quality out on our dock and in our fish tank. Having two projects helps leverage what we develop.

Temp was easy. Salinity was a pain, but now that I've seen the nuts-volts article, I think I could redo my hydrometer setup with a lot more accuracy. My induction attack was too crude. Water clarity was through a light sensor / led and for what we needed, accurate enough. Needs to be cleaned monthly. PH is the same, but we need to calibrate every month. Easy to do but annoying. The dock uses a flow meter. We treat it like wind speed.

Temp/flow done with one-wire, hydrometer through induction, PH/Turbidity through A2D. All using objects on the forum except induction and that will be when I get some time. I'm not wildly happy with my code, in fact, it generally looks sloppy, but we have had fun.

I never found a cheap ORP probe that could work without getting up to the 100+ dollars range. I tried hacking a Seapoint sensor but that was expensive also.

Thanks