My brain is fried. Ive spent the last two hours searching diy PH controller projects.
First, most of them are NOT controllers - they are just meters = waste of time. The ones which are actual controllers, for the most part, are using pre-built controllers and just add a pre-built pump. The others are again way to complex - they do C02, TDS, EC, etc etc etc., with thousands of lines of code. I did find one that looked promising, until I saw he was using a custom board that you needed to etch yourself.
So, no luck so far.
Well, I did find several sources for probes. The mini from Atlas looks pretty good for around $50. There are cheaper ones - like the Gravity - but it has bad reviews. I guess it wont last if left in constant contact with the solution, so that wont work,