Getting Started & beyond

7. Automatic Control

      7.1. Water

Digiplant’s key feature is the water controller for automatic watering.
When a plant is monitored through a soil moisture sensor, the data tends to always follow the same trend, as drawn below.

The descending slope of this saw-tooth will vary according to the plant type, size, age, climatic conditions, and so on.
This slope is a good indication of a plant’s draining capability and vitality: steeper slope is most likely to indicate higher metabolism thus healthier plant.
Let’s zoom at the watering moment.

The watering process, either manually or by an automated irrigation system, always follows these steps:
1. Water is poured into the soil
2. Soil sensor measures a quick rise
3. Water spreads into the soil in all direction
4. Soil moisture decreases to a steady-state level
This cycle is repeated until moisture steady-state is close to target.

Note: in the above example, moisture rises to 100% but it can also rise to a lower value, depending on the water quantity poured into the soil. A good illustration is a drop-by-drop irrigation system, where each watering increases the moisture only by a small amount. See below.

There are 5 important parameters:
• Moisture Min [%]
• Moisture Max [%]
• Time On [s]
• Time Off [s]
• Cycle Max
You can tune each of these parameters according to your plants need.

Obviously, for the water controller to operate, a soil sensor and a pump (or valve) must be connected.
Soil 1 is linked to OUT1, Soil 2 to OUT2, and so-on.

3-steps cycle:

  1. If soil measurement is inferior to Moisture Min, a new water cycle starts.
  2. Output is ON for Time On seconds, then OFF for Time Off seconds.
  3. Water controller checks if the new soil measurement is above Moisture Max. If not, cycle is repeated.

This cycle is repeated up to Cycle Max, until soil measurement is above Moisture Max. Then it stops and wait for the next soil moisture drop below Moisture Min.

There are two safety conditions to protect the system.

First safety condition:
After first watering cycle, if soil moisture is not above Moisture Min it is considered a failure state, thus entering safety mode.
Two possible reasons:
• Irrigation system is not working properly
• Soil sensor is not positioned properly
This is a safety in case the water is not reaching the soil, to avoid flooding the floor (been there).

Second safety condition:
After all the watering cycles (Cycle Max reached), if soil moisture is not above Moisture Max it is considered a failure state, thus entering safety mode.
Two possible reasons:
• Parameters are not tuned properly (Moisture Max too high ? Cycle Max too low ?)
• Soil sensor is not positioned properly
This is a safety to indicate to the user to improve the watering tuning.

Those two safeties simply disable auto loop and send you a notification.