PH/Temp data into a computer

[alanmorehead]

What is the current consensus on the pH/temp interfaces for the DIY Reef Controller project?

I am looking for the cheapest way to take a BNC pH probe and get data into the computer. So far, the best option I have found is the phidgets pH sensor (Link (http://www.trossenrobotics.com/store/p/4139-Ph-Sensor.aspx)). However, $81 seems a little high for this single input device. Isn't there something out there that is more in the range of $10-$20. Is there a schematic for this component that I can build myself?

I have seen the Venier GoLink devices, but the cost is $59 for the DAQ adapter and $78 for the probe. The probe replacement costs would end up killing me. That's why I am looking for a BNC connection.

Is there another option besides BNC or the GoLink for pH input?

Also, same thing for the temp probe/DAQ. What is the cheapest option for doing constant temperature monitoring into the computer?

I need to figure out if I will just be better off buying an Aquacontroller Jr.

[ufans]

I vote for the 1-wire Dallas Temp (DS18S20) -> USB and the pH Monitor->A/D Converter 1-wire (DS2450) -> USB

If you aren't a true DIYer then you might be better off with the Aquacontroller Jr.

[jimbob321]

i have a fan-less via computer i want to use as a controller monitor.. and have been looking at how to get ph temp info to it.. this is what i am thinking of doing http://cgi.ebay.com/Home-Automation-USB-DAQ-28-GPIO-8-ADC-4-DAC-4-PWM-UART-/120619865933?pt=LH_DefaultDomain_0&hash=item1c1581174d + you can use a relay board with the daq to control power recpticals .
and there are usb temp probe's
there is even 4 pwm's for dimming lights only 5v so you would probably need to build some circuit for that to raise it to 10v
this gets ph to the daq..
http://www.phidgets.com/products.php?product_id=1130

oops didnt see how old this post was

[ufans]

I'd recommend Hobby-Board's 8-Channel Relay (I use it and love it)
http://www.hobby-boards.com/catalog/product_info.php?cPath=24&products_id=1554

It includes the 1-Wire controller chip and the direct RJ-45 interface.

[Roamer]

Temp is easy. I'm currently looking at building a small temperature controller and I am thinking pretty hard about the DS20S18 part. It's got good accuracy and it is pretty easy to interface to an MCU.

The pH probe is a whole 'nother ball of wax! You can't just stick a meter to the output and measure it (not even a high dollar 6 1/2 digit bench meter!), as the probe's resistance is SO high that the meter WILL load it down and you won't read much of anything. ORP probes are similar, but not nearly as bad as a pH probe.

Even the input on an ADC will load it down too much. Pretty much the only way to do that is build a pH probe amp using an opamp that has VERY low input current (fempto amp range works nice), but opamps that can do this tend to cost a lot of money ($15+ each) and you will still need another opamp (but one with much less critical characteristics) to use as a differential voltage amp to center the output in the middle of your ADC's range (remember, pH probes output both positive AND negative values depending on the pH) and add some gain (3-3.5 to 1 or so assuming +5V VCC) to get the output to use most of the full scale of your ADC.

I just finished building and partially testing (with an old ORP probe) a pH amp that appears to do the job, but I need to write some code for one of my ATmega168 prototyping boards before I can say it works as it should with a real pH probe. I would be happy to share the circuit and the code once I have it all working.

[Roamer]

That link Jimbob posted would definitely be the easier way to for the pH probe interface. It's probably not as absolutely accurate as the amp I built, but it appears to be more than good enough for monitoring the pH of an aquarium.

[Mr.Biggs]

A note of caution on that solution from page 8 of there manual.

"Words of Caution
The pH Adapter Board should be used to measure solutions that are ‘electrically quiet’.
Measuring pH in electrically noisy environments such as tanks with mixing pumps, and even other measuring devices, is not recommended."