Who built their own PLC based controller?

[MelodyCorals]

This is all really good information, and I have been looking around more myself, and seems like you all are finding some of the best things so far (although over $500 is obviously a bit high). I'm debating about going down the reverse engineering approach on this, and just buying a probe and start hacking..... just not sure I will have the time any time soon to do it.

Here is some stuff I have found on RC:
http://www.reefcentral.com/forums/showthread.php?threadid=728247

and the forum discussing building your own controllers:
http://www.reefcentral.com/forums/forumdisplay.php?forumid=145

And another PHMA (for price, all they say is "fabulous price"):
http://www.sensorex.com/support/specifications/download/pHMASpecs.pdf

Also available at a possibly better price is this:
http://www.trossenrobotics.com/store/p/4139-Ph-Sensor.aspx
http://www.trossenrobotics.com/images/productdownloads/PhSensor1058.pdf

This last one from trossen seems fairly simple - and if you had it, you might be able to reverse the idea out of it fairly simply as it looks like most of the chips on the PCB would be for the USB aspects of it.

I admit I have not fully scanned this yet, and so maybe the answer is in here somewhere. If someone finds a good one, let us know.

Thanks,
Josh

 

[MelodyCorals]

I love it when I can answer my own questions (with some help of course). I contacted my favorite AVR forum for some general questions, and sure enough - we have an answer:

http://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&p=327441#327441

The short of it is that this has already been done, and the instructions with schematic are here:

http://www.66pacific.com/ph/ph_1.htm

Thanks,
Josh

-- EDIT --
And the more you know what to search for... the more you find:

http://damien.douxchamps.net/elec/ph_meter.php

 

[Jacob D]

Hey Josh, you've been busy researching!

I didn't read through ALL of that, but some. Just wanted to point out a couple of things...

If you're building a PLC based controller you'll need 4-20ma output. If your controller is not PLC based then you most likely don't need the 4-20ma signal. At least I don't think you would if you're using digital components. If that's the case then you don't need the "interface" on the Omega website that gives you the 4-20 signal, you just need a probe and your circuit.


I did come across another interesting item on Omega. This one accepts PH _and_ Conductivity (salinity) at the same time and has 2x 4-20ma outputs. This is exactly what I need (if only it had temperature too!). I'm just trying to clarify a couple of things with an Engineer at Omega, then I'll most likely purchase it along with the probes and calibration fluids. All together it'll run about $600... and I still need a temp transmitter. So maybe $900 to monitor and control these 3 major params via. PLC.

 

[funman1]

I can get you the temp controller for like 90 bucks.
There's a place up here called something "Control"
I bought mine off them for like $90 bucks and it's a 4-20 that's what I use for my temp control.

 

[Jacob D]

Let me know about that, you have a link to the one you used?

 

[funman1]

I don't..
Here is their phone numbers
There are two businesses in that building, one makes control boards and the other sells refgeration equipment.

Ask for the one that makes stuff. (Total Control)
You want the stainless steel Temp probe.

Rsd/Total Control
(916) 780-7220

Total Control
(916) 780-5929

I swear I had a pic of mine installed in my sump but can't find it!?!?!?

 

[Jacob D]

Cool, thanks.

I'm going to scrounge around a little and see if I can find something for free (or cheap). If not I'll check into that one.