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Hydroponic nutrient solution controller

Features:

  • monitors solution pH
  • adjusts pH by adding nutrients
  • monitors temperature of solution or root zone
  • uploads data to the cloud (Google, Thingspeak)
  • fail-safe design

Photos:

Hydroponic system

Recirculating hydroponic system consists of solution tank and a fresh water tank. Solution tank is used to both mix and hold the solution. Solution consumed by plants is continuously replaced with a fresh water from the fresh water tank through a float valve.

Sensors

Following data is obtained by the controller:

  • temperature of solution or root zone
  • pH of solution
  • solution presence (float switch)
  • fresh water level (pressure sensor at supply tank)

Data storage

All sensor readings are stored online in a Google sheet.

In order to simplify monitoring, sensor readings are also uploaded to the Thingspeak service. Data from Thingspeak can be easily viewed with a mobile app.

Regulation

In a setup where consumed solution is replaced with a fresh water it is enough to adjust pH by addition of new nutrients. Practice shows that EC value stays within an acceptable range and requires no control.

This controller implements a discrete proportional regulation algorithm. At each iteration, a pH state of the solution is measured. Then, nutrients are added in amount proportional to the difference between actual and desired pH.

Error handling

If an error happens during the initialisation stage it will lead to the program termination.

After controller has entered the iteration loop, only a specific set of errors will cause the program termination (fatal errors). Transient errors like network issues will thus not result in a denial of service.

A fatal error will be thrown if there is a chance that controller state can become inconsistent or there are other factors that can lead to a crop loss (e.g. if pH is out of a reasonable range).

All errors are reported to syslog and can be viewed with logread. Error history will be kept in RAM until next reboot. There is no cheap reliable way to save log in a persistent storage.

Monitoring

Properly operating controller will submit results to the database on a strict schedule. If there are no new records appearing in the database, connect to the controller and check for errors in /tmp/hydroctrl.err and logread.

Hardware

  • Raspberry Pi 3
  • pH
    • MinipH pH interface by Sparky's Widgets (note: voltage reference IC has to be soldered manually)
    • REF3025 voltage reference (if not present on the interface)
    • I2C opto isolation by Sparky's Widgets
    • pH electrode with BNC plug
  • DS18B20 temperature sensor
  • Float switch for solution tank
  • Nutrient pump
    • Peristaltic pump with stepper motor (nutrient pump)
    • Big Easy Driver stepper motor driver by Brian Schmalz
  • Water consumption
    • MP3V5050DP pressure sensor
    • REF3030 voltage reference (to supply the sensor)
    • ADS1115 ADC board
  • Supply
    • DC-DC step down converter 12V to 5V 5A
    • 220V to 12V 3A Class I SMPS

Bus usage

  • I2C
    • pH meter
    • pressure sensor
  • 1-Wire
    • temperature sensor
  • GPIO
    • nutrient pump
    • float switch

Hardware setup

  • Make sure peristaltic pump properly compresses the pipe in all rotor positions. In my case, pipe holder had to be tightened to prevent free liquid flow in some positions.
  • Output end of the nutrient pipe must be placed higher than nutrients level to prevent free flow (in case pump clamp becomes loose).
  • Solution in the tank must be mixed, e.g. with aquarium pump. In my case nutrients would not reach pH sensor in hours, and controller would keep pumping them.
  • Easy Driver
    • Replace pullup with a pulldown at SLEEP pin.
    • Solder a 3.3V jumper.
    • Adjust current to match stepper motor rating.
  • MinipH
    • Remove the SJ1 jumper
    • Solder a voltage reference IC (e.g. REF3025)
    • Solder a 3.3V jumper on the I2C opto isolation
  • Solder power supply wires directly to the RPi board (Micro USB plug is not reliable).
  • Pressure sensor
    • MP3V5050DP sensor is ratiometric and must be supplied with a stabilized voltage.
    • Make sure there're no air leaks in sensor piping. E.g. submerge the open end of the sensor pipe in water 20..30 cm deep. Pressure should not change by more than 1 cm H2O over 24 hours period.

Software setup

  • OS installation and basic setup

    • dd Raspbian Lite to SD flash

    • create empty file ssh on the boot partition (enable ssh server)

    • edit /etc/wpa_supplicant/wpa_supplicant.conf (configure WiFi)

      network={
ssid="SSID"
psk="WIFI PASSWORD"
}

    • power on

    • discover raspberry with arp-scan -l

    • connect via ssh (user pi, password raspberry)

    • sudo apt-get update && sudo apt-get upgrade

    • sudo apt-get install vim

    • sudo raspi-config

      • Boot Options
        • Desktop / CLI
          • Console
        • Wait for Network at Boot
          • No
      • Interfacing Options
        • I2C
          • Yes
        • 1-Wire
          • Yes

    • mkdir ~/.ssh and paste your public ssh key into ~/.ssh/authorized_keys.

      Logout ssh and login again without password.

    • sudo usermod --lock pi (disable login with password)

    • sudo dpkg-reconfigure tzdata (set time zone)

    • edit /etc/network/interfaces (disable WiFi power management)

      allow-hotplug wlan0
iface wlan0 inet manual
    wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf
    wireless-power off

      Reboot and make sure power management is off (check with iwconfig).

  • Switch to readonly FS

    • follow these instructions (skip the fake-hwclock script)

    • sudo mount -o remount,rw /

    • create scripts to manually remount FS: /usr/bin/rw:

      #!/bin/sh
sudo mount -o remount,rw /

      and /usr/bin/ro:

      #!/bin/sh
sudo mount -o remount,ro /

      sudo chmod +x /usr/bin/rw /usr/bin/ro

    • sudo apt-get purge fake-hwclock

    • edit /etc/rc.local

      # Fix tmpfs permissions
chmod 1777 /tmp

# Fix ntp trying to create a temp file in /var/lib/ntp/
mkdir -p /tmp/ntpfs/upper /tmp/ntpfs/work
mount -t overlay overlay -olowerdir=/var/lib/ntp/,upperdir=/tmp/ntpfs/upper,workdir=/tmp/ntpfs/work /var/lib/ntp
chown ntp:ntp /var/lib/ntp

    • edit .vimrc

      set viminfo="/tmp/viminfo"

  • Configuration

    • Install runtime
      • sudo apt-get install git python3 python3-pip libffi-dev
      • git clone https://github.com/pzankov/hydroctrl.git
      • sudo pip3 install -r ~/hydroctrl/requirements.txt
    • cd ~/hydroctrl
    • Google sheet
      • create a google spreadsheet and remove all rows but the first one
      • save spreadsheet ID to google_sheet_id.txt
      • obtain google credentials for gspread as described here. Don't forget to share the spreadsheet with the email specified in json_key['client_email'].
      • save credentials to google_key.json
      • run ./google.py to append a sample record
    • Thingspeak
      • create a Thingspeak channel with the same order of fields as in settings.DATA_SPEC (skip the date field)
      • save the channel's write api key to thingspeak_key.txt
      • run ./thingspeak.py to append a sample record
    • Temperature
      • run ./temperature.py and check that temperature sensor works
    • pH
      • verify settings.PH_CONFIG
      • run ./ph.py to see pH sensor status
      • pay attention to the signal noise (see paragraph below)
      • adjust calibration data
    • Supply tank
      • verify settings.SUPPLY_TANK_CONFIG
      • run ./water_tank.py to see pressure sensor status
      • adjust calibration data
    • Solution tank
      • verify settings.SOLUTION_TANK_CONFIG
      • run ./solution_tank.py to see solution tank status
      • check that solution tank status is affected by float switch
    • Nutrient pump
      • verify settings.PUMP_CONFIG
      • run ./pump.py 10ml to pump 10 ml of liquid
      • adjust steps_per_volume
    • Controller

      • verify settings.CONTROLLER_CONFIG

      • run ./controller.py

        An iteration has to be started every settings.CONTROLLER_CONFIG['iteration_period'].

      • edit /etc/rc.local (start controller at boot)

        # Start controller
sudo --user=pi PYTHONUNBUFFERED=1 /home/pi/hydroctrl/controller.py >/dev/null 2>/tmp/hydroctrl.err &

      • reboot and check that controller is running with ps aux | grep python

pH noise

If pH signal noise is too high (greater than ±30mV), use the oscilloscope.py script to determine its source.

Running oscilloscope.py without arguments will render a test signal.

Run ph_adc_server.py on RPi and oscilloscope.py RPI_IP on the host to monitor live oscillogram and spectrogram of the pH signal.

If there is no distinct 50 Hz spike on the spectrogram, then most likely you are dealing with a high frequency common mode noise produced by the SMPS. pH sensor opto isolation does not completely block high frequency common mode noise.

Here is a table of noise levels obtained with different power supplies. Solution tank was floating with all plastic piping.

Power supply type Noise stdev
Transformer, unregulated 1 mV
Class I SMPS 3 mV
Class II SMPS 30 mV

Dev tools

These are my personal dev env settings.

  • edit /etc/locale.gen, uncomment en_US.UTF-8, then run sudo locale-gen
  • sudo apt-get install tig fish vim-python-jedi ipython3 time wcalc
  • vim-addons install python-jedi
  • git clone https://github.com/pzankov/cfg.git
  • ./cfg/install.sh