Demeter

Demeter is an Arduino & Raspberry Pi-based hydroponics robot.

Presently, it tracks:

• water level high (redundant float switches)
• water level low (redundant float switches)
• water pH
• water temperature
• water TDS (Total Dissolved Solids ppm)
• volume of distilled/RO water dispensed
• volume of pH buffer dispensed

-and controls:

• a 5v magnetic stirrer for pH buffer solution administration
• a 12v peristaltic pump for pH buffer solution administration
• a 12v peristaltic pump for distilled/RO water auto-top-off
• a 12v submerged pump for reservoir circulation

-while logging to:

• redis
• AdaFruit.IO

Tested on a 13 year old peace lilly.

System Tour

Redundant Float Switches

These floats still need to be shrouded to protect them from tangling roots. For both min and max water levels, two float switches are wired in series.

Max Level Floats

The maximum level float switches are oriented normally-closed. Only one max level switch needs to open (rise) for the system to respond.

Min Level Floats

While also wired in series, the minimum float switches are, however, oriented normally-open. Both minimum floats must close (sink) before the system will respond.

Peristaltic Pumps & Magnetic Stirrer

Water ATO (Auto Top-Off) and pH buffer solution pumps. The buffer needs to be mixed prior to pumping. An additional, third pump inside the reservoir circulates the water during buffer administration.

Control Board

The control board has 3 different DC voltage circuits:

• 3.3v via Arduino (TDS sensor)
• 5v via Arduino (pH sensor, magnetic stirrer, temperature probe)
• 12v via external power supply (2 peristaltic pumps, 1 circulation pump)

-and includes:

• Arduino Uno
• Raspberry Pi 4 B
• 128x64 OLED display
• 8 channel relay board
• 4 channel logic level shifter
• pH sensor board
• TDS sensor board