Few things up front regarding the whole ‘app’ idea; Making an iOS app is no trivial task, moreover, it’ll cost you at least $99/year for a developers licence, not to mention the fact that you need an Apple computer for Xcode. And that doesn’t even include the fact that you need to know how to actually use said software, and the fact that you’ll have to learn how to program that in less than a week or so. You’ll also need some kind of server to log your data when you’re not using the app.
The webapp is less difficult in the way that it doesn’t have any software requirements or mandatory fees. It will also run on all platforms. The problem here however lies in the fact that you’ll need a place to host that page on, and some kind of server which continuously logs your data.
The server side could be done with node.js, but you’ll need a place to host that on as well. If you’ve got a raspberry pi, or some other device that’s permanently connected, you could use that, otherwise you’ll have to find an external host for that as well. Also, you’ll need to code the necessary node.js code (javascript, which could fortunately be the same as the webapp).
Considering all of the above, the time constraints, and your (lack of) programming skills, I would highly recommend checking out one of the online options I mentioned in my previous post. They are capable of running on all platforms (it’s webbased), they have datastorage included, they have hosting included, they have data visualisation included. That pretty much sums up all of your requirements. There’s some sort of proverb about wheels, and the fact that you may not want to reinvent them. I’ve got a hunch that might be applicable here ;).
The other concern is the available data. Unless you’re going to stick in a PH sensor, there’s hardly a way of telling the PH values at any given time. Seeing as PH sensors are rather expensive and cumbersome so set up, I think I may have an alternative. What if, instead if measuring the PH value, you measure the flow rate, and use that to calculate the PH values (approximately). It should be basic chemistry that when you mix X amount of Basic stuff with Y amount of acidic stuff, you get a PH of Z. If you know how much acid you’ve got, and you can measure the amount of basic stuff that’s being pumped into it, you not only have the total amount of combined liquid, but are also able to calculate the PH values. You can use one of these flow meters to measure the amount of liquid that’s being pumped. I can’t guarantee that’s it’s going to be incredibly accurate, but then again, a home-made copper conductivity sensor, orange juice, and baking soda probably isn’t going to be that accurate either
Maybe there are some alternative ways of measuring the output of your circuit (voltages, current, resistance of conductivity sensor), but I feel more comfortable asking @bko or perhaps @kennethlimcp for some ideas regarding that.
Unrelated side note: in the future, please don’t edit your posts so dramatically. It’s going to be confusing for other readers when the responses don’t match up with the post being responded to. Most of the question in my first post have now been erased from your original post, which is kind of messy. If you feel like adding additional information, just put it at the bottom of the post, preceded by “Edit:”. That’ll make it easier to understand. Thanks in advance!
@kennethlimcp, I’m not sure where you’ve seen that he’s using an Arduino, because it looked all analog to me(?)