DIY Controller (Atmel based)

[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!

[kwirky]

what's that on the far lefthand side that was cut off in the schematic labeled "X1"?

What about having software callibration? Which pots would be cut out for software callibration? (for example, put probe in ph 7 solution, press button. put ph probe in ph 10 solution, press button)