7. Automatic Control
7.1. Water
Digiplant’s key feature is automatic watering.
When a plant is monitored with a soil moisture sensor, the data tends to always follow the same trend:
Example with a few cacti (web app):
The descending slope of these saw-tooth will vary according to the climatic conditions, plant type, size, age 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, either manually or automated, always follows these steps:
1. Water is poured into the soil
2. 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 reaches target.
Note: in the above, 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/valve must be connected.
OUT1 is linked to S1, OUT2 to S2, and so-on.
After activating auto mode, the watering cycle follows these steps:
- If soil measurement is inferior to Moisture Min, a new water cycle starts.
- Output is ON for Time On seconds, then OFF for Time Off seconds.
- Water controller checks if the new soil measurement is above Moisture Max. If not, step 2 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 the 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
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
• Soil sensor is not positioned properly
Those two safeties simply disable auto mode and send a notification.