interfacing PPM / TDS probe to arduino

[ryandamartini]

After recently going to the hydroponics store and seeing a $3000.00 box that automates the garden, I want to of course make my own said box for my tomatoes, peppers, and herbs

I do realize this is a first post so I will give some info on myself. I am not a complete noob. I earned most of a computer engineering degree from FSU before I fell into the world of horticulture which I really am just in love with now and will be moving to UGA next semester.

I am working on using a BeagleBoard using the tut in the blog on interfacing arduino to it. The BB will provide a web interface while logging data allowing me to gather cool data about my plants I have so far gotten temperature, light, ph, and humidity running through a console. My first step is to just get it reading everything.

The PPM / TDS solutions out there have just killed me. Vernier offers an analog conductivity (tds) meter. http://www.vernier.com/probes/con-bta.html
http://www2.vernier.com/booklets/con-bta.pdf

Pinouts: http://www.vernier.com/probes/specs/pinout.html

I think I lack the experience to take it further. I am at the point of offering some cash for a PPM interface I can make for my box. Eventually, the entire project will go open source to empower indoor growers everywhere.

Thanks in advance. I am stumped. Any electrical gurus out there post up! I did search the forums first as well.

Thank You!
-Ryan

[PaulS]

I am working on using a BeagleBoard

And your Arduino related question was?

[ryandamartini]

the arduino is plugged into the beagleboard

I am using the BB as a playground / data collection / interfacing tool for the arduino. My problem is with getting a PPM probe to work with the arduino.

Thanks,
-Ryan

[cmiyc]

I guess your post is asking for help with PPM /TDS?  Sounds fun. What are they?

[ryandamartini]

Like I posted, I am refusing to pay $3000 to automate my indoor veggie/herb supply. So I am making my own box to do it. The parts per million (PPM) probe is also known as a TDS (total dissolved solids) probe. This lets me measure the concentration of salts (nutrient concentration) in the water.

I need help with interfacing a PPM/TDS probe to an arduino. The only one I could find that looks promising to start (maybe) is the Vernier model posted above.

Thanks!
-Ryan

[ryandamartini]

Bump. Really need some guidance here!

[zoomkat]

Bump. Really need some guidance here!

Well, you really need to explain how the TDS probe operates. Generally most probes operate by changing voltage/current supplied to the probe in some fashon (capacitance could also come into play). Explain the operating principals of your probe.

[ryandamartini]

@Richard:

I got the vernier device information from threads I had searched on the forums here and had posted it up. I was hoping some progress had been made with PPM since that thread. I will try to post some more information.

@Zoomkat

I am really aiming to use a premade probe for PPM readings. What a PPM probe does though, is generate a current in a solution and the strenght can be measured and displayed in PPM after some conversions. You *can* make your own probe, but most of the methods I've seen leave me skeptical of their accuracy.

The competition, GroBot uses Sensorex sensors. Right now, I can interface their pH sensor through a wonderful device made by phidgets. http://www.phidgets.com/products.php?category=6&product_id=1130 . It allows me to plug in a sensorex probe or a slightly cheaper one for development purposes and the analog goes into the arduino. My goal is to use this probe from sensorex : http://www.sensorex.com/products/conductivity_sensors/lab/conductivity_lab_sensors.html for tds readings. I am just at a loss of getting the TDS probe to talk to arduino.

I hope that clarifies things and apologies for being short in my earlier posts.

Thanks,
-Ryan

edit:
I called sensorex and got a wonderful guy on tech support that recommended one of these: http://www.sensorex.com/products/conductivity_sensors/accessories/conductivity_transmitters.html and an op amp circuit. He didnt go into any more detail than that.

more data on box: http://www.sensorex.com/support/specifications/download/CT1000Specs.pdf

[ryandamartini]

@ Richard

You are correct. In school, we used the terms pretty much interchangeably. I'm definitely wanting to stay away from building my own instrumentation and is why I am wanting pre made, laboratory proven nodes for measuring.

I do have one of the phidget devices talking with the pH probe. I will write down some numbers and do some math. If there is a way to convert readings or adjust them for accurate PPM reading with the phidget, I am all game. The probe is just very expensive.. heh

[zoomkat]

Just remember that to make vey exacting measurements with high end equipment that you will probably need a very exacting lab environment.

[ryandamartini]

@zoomkat

The probes used are designed for continuous in line measurement and will be running on lines away from the pumps.

[zoomkat]

If it is going to be used in a process line with a lot of unknown chemicals in the solution, it may not be any more useful than a simple PH measuring setup. Just a heads up on the return you may get for a significant $$$ outlay.

[ryandamartini]

I really need the ppm to just get an idea of how much nutrient solution is circulating. Ghat is the main reason for it. Measuring tds is crintical to hydroponics.

[ryandamartini]

Even so, I'm still at a loss for interfacing the PPM probe. Phidgets only makes a pH. From reading their forums, there hasn't been much luck from using it with a ppm probe of any sort.

Edit:

May have found something, looking for the output on the probes. WIll post back.

[ryandamartini]

Just thought I would give an update on the project. I have figured out there is no cheap way to get a good TDS / PPM reading and need a conductivity transmitter then send that to something that lets the arduino pick it up. Will post back with some details for criticism and some ideas from people more experienced with this lil' chip.