Dyah Setyaningsih

Project idea: https://miro.com/app/board/uXjVLBm7F8w=/?share_link_id=117991010729

Motivation

Are my plants breathing? They seem fine, their leaves are green... but are they really okay? To observe my houseplants' respiration, a prototype of soap bubble maker machine is being developed. The quantity of soap bubbles will be in accordance to the CO₂ level of the plants' (closed) environment, divided into three categories: Low, Medium and High CO2 level.

Materials

• ESP32
• CO₂ sensor MH-Z19C
• Stepper motor 28BYJ-48
• Stepper motor driver module ULN2003
• PWM fan AMD Ryzen 7 1700
• 10kΩ resistor
• Power supply 12 volts
• Switch
• Lots of cables...

To-Do List

• Implement stepper motor speed (based on category (CO₂ value)) (s. Pseudocode below)
• Solve technical problems (failed to connect with ESP32? Stepper motor not working after extending wires? Unstable wires?)
• Stabilize bubble rings holder to the stepper motor (done)
• For better and more directed air flow: add nozzle/funnel? (done, but is air flow strong enough?)
• Make wiring diagram
• Documentation

Pseudocode

Idea: assign CO₂ value into 3 categories; Low, Medium, High and adjust the stepper motor speed based on the category.

  DEFINE constants for CO2 thresholds:
    LOW_MEDIUM_THRESHOLD = 500 //to be determined via trials
    MEDIUM_HIGH_THRESHOLD = 700 //to be determined via trials
  
  DEFINE speed settings for each category:
    LOW_SPEED = 400      // Steps per second
    MEDIUM_SPEED = 800   // Steps per second
    HIGH_SPEED = 1200    // Steps per second
  
  INITIALIZE variable currentCategory to -1
  INITIALIZE variable lastCategory to -1
  
  FUNCTION setup():
    BEGIN
      SET maximum speed for stepper motor (e.g., 1200 steps/sec)
      SET acceleration for smoother operation (e.g., 500 steps/sec^2)
      START serial communication for debugging
    END

  FUNCTION loop():
    BEGIN
      READ CO2 value from the sensor (variable CO2)
      
      DETERMINE currentCategory:
        IF CO2 < LOW_MEDIUM_THRESHOLD:
          SET currentCategory to LOW
        ELSE IF CO2 < MEDIUM_HIGH_THRESHOLD:
          SET currentCategory to MEDIUM
        ELSE:
          SET currentCategory to HIGH
      
      IF currentCategory is different from lastCategory:
        BEGIN
          SWITCH currentCategory:
            CASE LOW:
              SET stepper motor speed to LOW_SPEED
            CASE MEDIUM:
              SET stepper motor speed to MEDIUM_SPEED
            CASE HIGH:
              SET stepper motor speed to HIGH_SPEED

          UPDATE lastCategory to currentCategory
        END
      
      RUN stepper motor at the current speed (use AccelStepper's runSpeed() function)
    END

Idea to determine thresholds: run trials on plants enclosed environment.

  DEFINE variables:
    minCO2 = Infinity     // Initialize to a very high value
    maxCO2 = -Infinity    // Initialize to a very low value
    startTime = CURRENT_TIME
    trialDuration = 30 minutes (in milliseconds, e.g., 30 * 60 * 1000)
  
  FUNCTION setup():
    BEGIN
      INITIALIZE serial communication for debugging
      INITIALIZE CO2 sensor
      PRINT "Starting 30-minute CO2 trial..."
    END
  
  FUNCTION loop():
    BEGIN
      WHILE (CURRENT_TIME - startTime) < trialDuration:
        BEGIN
          READ current CO2 value from sensor (variable currentCO2)
          
          IF currentCO2 < minCO2:
            UPDATE minCO2 to currentCO2
          
          IF currentCO2 > maxCO2:
            UPDATE maxCO2 to currentCO2
          
          PRINT currentCO2, minCO2, and maxCO2 to serial monitor
          WAIT for 1 second //reduce sampling frequency
        END
      
      PRINT "Trial Complete."
      PRINT minCO2 and maxCO2 to serial monitor
      
      CALCULATE range = maxCO2 - minCO2
      CALCULATE lowMediumThreshold = minCO2 + (range / 3)
      CALCULATE mediumHighThreshold = minCO2 + (2 * range / 3)
      
      PRINT "Thresholds:"
      PRINT "Low-Medium Threshold: " + lowMediumThreshold
      PRINT "Medium-High Threshold: " + mediumHighThreshold
    END

Gallery

The Plant Plant Gallery (Nextcloud Bauhaus Uni), Password: theplantplant (CO₂ sensor first trial pictures are inside)

References

CO₂ sensor MH-Z19C

• https://www.neumueller.com/datenblatt/neumueller/MH-Z19C.pdf (Datasheet)
• https://randomnerdtutorials.com/esp32-uart-communication-serial-arduino/ (Concept, wiring, code)

PWM fan AMD Ryzen 7 1700

• Arduino Fan Control using High Frequency 25kHz PWM // 4-Wire CPU Fans - YouTube (Concept, wiring, code); adapted to ESP32

Stepper motor 28BYJ-48 and stepper motor driver module ULN2003

• https://randomnerdtutorials.com/esp8266-nodemcu-stepper-motor-28byj-48-uln2003/ (Concept, wiring, code); adapted to own implementation