Since a bunch of you might have the board ready soon, just wanted to point out that there is one hardware configuration step for the PH - calibration.
It is quite straight forward and there are 2 ways to do it - with LCD or with multimeter.
Prerequisites:
7.00 PH Calibration fluid
10.00 PH Calibration fluid
4.00 PH Calibration fluid (optional)
LCD:
For this method you need to have your LCD connected and a firmware uploaded to the main AVR that will display the PH value.
- Connect your PH Probe to the BNC connector
- Power up Hydra with PSU (5V from usb cable will not work, the PH circuit requires more than 5V to work)
- Dip your probe in RO/DI water to wash it.
- Now dip it in the 10.00 PH fluid. Leave for a few minutes. When you come back, adjust RV3 until the display reads the corresponding PH for the corresponding temperature (should be on your fluid packaging, usually 10.00 is @ ~77F). Leave for a few minutes. If the number has drifted, adjust.
- Repeat the above 2 steps with the 7.00PH Fluid and RV2.
- Repeat above 3 steps to make final adjustments.
(Optional) Dip the probe in the 4.00 PH fluid and wait a few seconds. The display should be pretty spot on (mine reads 4.01 which is good enough for me).
Multimeter:
The steps are basically the same, but instead of using the LCD to read the value, use a multimeter and read A3 on the main AVR. For 10.00 PH you should have 2.441V, for 7.00 you should have 1.709V. Now depending on the quality of your multimeter, the arduino LCD might be more accurate.
Ideally it shouldn't matter how you calibrate. But that's ideally
EDIT: now I have to see why the above don't match in my case
