For optimising your code you should analyse how fast does the ph-sensor react on ph-changes.
A microcontroller can run so fast that you could control 50 pairs of pumps with 50 ph-sensors at the same time
if the programming is done right.
There is a programming-technique caled non-blocking timing.
as an allday example with easy to follow numbers
delay() is blocking. As long as the delay is "delaying" nothing else of the code can be executed.
Now there is a technique of non-blocking timing.
The basic principle of non-blocking timing is fundamental different from using delay()
You have to understand the difference first and then look into the code.
otherwise you might try to "see" a "delay-analog-thing" in the millis()-code which it really isn't
Trying to see a "delay-analog-thing" in millis() makes it hard to understand millis()
Having understood the basic principle of non-blocking timing based on millis() makes it easy to understand.
imagine baking a frosted pizza
the cover says for preparation heat up oven to 200°C
then put pizza in.
Baking time 10 minutes
You are estimating heating up needs 3 minutes
You take a look onto your watch it is 13:02 (snapshot of time)
You start reading the newspaper and from time to time looking onto your watch
watch 13:02 not yet time
watch 13:03 not yet time
watch 13:04 not yet time 13:04 - 13:02 = 2 minutes is less than 3 minutes
watch 13:05 when did I start 13:02? OK 13:05 - 13:02 = 3 minutes time to put pizza into the oven
New basetime 13:05 (the snapshot of time)
watch 13:06 not yet time
watch 13:07 not yet time
watch 13:08 not yet time (13:08 - 13:05 = 3 minutes is less than 10 minutes
watch 13:09 not yet time
watch 13:10 not yet time
watch 13:11 not yet time
watch 13:12 not yet time
watch 13:13 not yet time
watch 13:14 not yet time (13:14 - 13:05 = 9 minutes is less than 10 minutes
watch 13:15 when did I start 13:05 OK 13:15 - 13:05 = 10 minutes time to eat pizza (yum yum)
You did a repeated comparing how much time has passed by
This is what non-blocking timing does
In the code looking at "How much time has passed by" is done
currentTime - startTime >= bakingTime
bakingTime is 10 minutes
13:06 - 13:05 = 1 minute >= bakingTime is false
13:07 - 13:05 = 2 minutes >= bakingTime is false
...
13:14 - 13:05 = 9 minutes >= bakingTime is false
13:15 - 13:05 = 10 minutes >= bakingTime is TRUE time for timed action!!
if (currentTime - previousTime >= period) {
it has to be coded exactly this way because in this way it manages the rollover from Max back to zero
of the function millis() automatically
baldengineer.com has a very good tutorial about timing with function millis() too .
There is one paragraph that nails down the difference between function delay() and millis() down to the point:
The millis() function is one of the most powerful functions of the Arduino library. This function returns the number of milliseconds the current sketch has been running since the last reset. At first, you might be thinking, well that’s not every useful! But consider how you tell time during the day. Effectively, you look at how many minutes have elapsed since midnight. That’s the idea behind millis()!
Instead of “waiting a certain amount of time” like you do with delay(), you can use millis() to ask “how much time has passed”?
This means your loop runs through tenthousands of times every second always comparing how much time has passed by since last timed action. And if the time that has passed by becomes bigger than your timeing-constant the next timed action gets executed.
So give it a try with a modified code-version - and - if it does not work yet as expected post your new coe-version and ask questions.
best regards Stefan