@Has If you have runoff, that means the media is 100% saturated and can hold no more water/nutrient solution. When growing in coco you always want to maintain at least 90% saturation, and you also want to maintain 15-30% runoff after every irrigation event depending on the size of container and a few other parameters. If you know that you watered with 1000 ml, then you need to see at least 150-300 ml of runoff. A moisture content sensor would be useless to try and automate this process, but a scale works perfectly. A moisture content sensor might work better in a soil grow, but a scale would still give you better information to work with.
The question of bottom and top irrigation is certainly debatable, but probably not in this section.
I imagined the "Scale based systems" as a pot with a plant standing on the scale and the scale signaling drying out (((
Now I looked at your system at
www.GrowTekUSA.com and everything became clear.
Of course, from the point of view of design, everything is very nice and neat, but let me make a few comments.
You measure the flow with unwarranted accuracy, although in reality the input data for the amount of water during irrigation are the results of the flow from the last irrigation, and then you apply the algorithm to make a rough adjustment. That is, you "very accurately" define "yesterday's weather".
Isn't it better to put the simplest moisture sensor on the drain path in order to record the moment the drain starts and then give a certain operating time for the pump supplying the solution in order to ensure your 15-30% of the percentages of the amount of water already spilled by this moment. You have a sufficiently high-quality and accurate dosage of the pump + controller water supply, so the excess spillage will turn out with any required percentage much more accurate than what you get now.
Of course, scales and pumps for pumping out the drain are no longer required, because the drain can already be made passive.
And one more little thing - your frame for hanging pots is comfortable for 1-2 plants.
But when scaling (4-8 pieces), it is probably better to use some kind of separate stands or pots with legs. This will allow you to arbitrarily move or rotate the bushes relative to each other as they grow (sometimes unevenly).
At the same time, you can save space and lighting.
Sorry for google translator.