DIY Controller (Atmel based)

[Robw]

I did find one schematic so far for a ph probe. The output from the circuit is 0-140mv which corresponds to the ph value. No link to the probe used though.
http://damien.douxchamps.net/elec/ph_meter/

Assembly language! I haven't used that in more than 20 years. I do remember it was fun once I figured out the codes etc. That was for the 8085 microprocessor. Time to start reading!

[mark]

Kwirky, once you get them running, sounds like a cheap little controller you could market to fellow reefers.

Robw, I was looking for the output for figuring the slope/intercept for a pH probe awhile back (was hooking to a datalogger) and got this e-mail from American Marine (AMI):
"After proper calibration the probe will generate 59 mV per each unit of positive pH and the opposite will be negative mV. Example pH 7.0= 0 mV; a ph of 8.0=59mV a pH of 6.5= -30mV Good Luck...Lou Dell/AMI"

[midgetwaiter]

Originally Posted by mark

"After proper calibration the probe will generate 59 mV per each unit of positive pH and the opposite will be negative mV. Example pH 7.0= 0 mV; a ph of 8.0=59mV a pH of 6.5= -30mV Good Luck...Lou Dell/AMI"

Did he by any chance explain how to correct for temperature with this? The closest I've ever found to a bona fide reference is the table on the back of pinpoint's calibration packets and I bet that doesn't necessarily correspond with SW.

[kwirky]

Originally Posted by midgetwaiter

Did he by any chance explain how to correct for temperature with this? The closest I've ever found to a bona fide reference is the table on the back of pinpoint's calibration packets and I bet that doesn't necessarily correspond with SW.

with the temperature we run our aquariums at temperature callibration is almost negligable. I saw a chart somewhere once and it's like a 2% difference. (ph 8.302 instead of 8.297)

[KrazyKuch]

Here is a schematic I just did up for an Orp interface

[kwirky]

does the orp interface work the same with a pH probe too? only the calibration points would be separate?

[KrazyKuch]

Yeah thats basically how all probes work.....All you have to do is amplifi the signal to a stat that is easily readable from your controller then it's a matter of figuring out how the signal gets converted into the proper reading.....for PH after it's amplified 1 millivolt will stand for a ph of 1 a 10 millivolt signal stands for a ph of 10....If you want I can get the calculations for the orp!