Plant Saver

The lesson begins with a discussion of the basic needs of plants.

Then the students play a scratch game created by teacher-collaborator Suzannа Martirosyan.

Link to the game here

After discussing the teacher asks questions:

“What do plants need to grow?”

How do you know if a plant needs water?

Do different plants need the same amount of water?

How can a plant’s soil tell us it needs water?

• The “Soil Type” Test (Geology)

The Setup: Take two cups—one filled with sand and one with potting soil.

The Action: Pour the same amount of water into both and insert the sensor.

The Observation: Watch the numbers on the screen. Does the sand “dry out” faster than the soil?

The Concept: This teaches soil-water relationships. Students learn that “moisture” depends on the texture and space between soil particles.

• Finding the “Wilting Point” (Biology)

The Action: Stop watering a test plant for a few days.

The Observation: Watch the plant closely. The moment the leaves start to droop or feel soft, look at the sensor reading.

The Goal: That specific number is the Permanent Wilting Point.

• The “Transpiration” Race

Students test how the environment “steals” water from the plant’s leaves.

The Setup: Group A puts their plant in the shade. Group B puts theirs in front of a fan or under a bright lamp.

The Action: Time how long it takes for the moisture levels to drop.

The Concept: Students will see that the plant in the “wind” or “sun” loses water much faster. This explains transpiration—how plants “breathe” out water vapor, especially when it’s hot or windy.

Discussing and introducing questions:

 What is Arduino? Explain that it is the “brain” of the project. Like a human brain receives signals from the skin (touch) and tells the hand to move, Arduino receives signals from sensors and tells LEDs to light up.

Input vs. Output: * Inputs: Sensors (Soil moisture, buttons, light sensor

 Outputs: Actuators (LEDs, buzzers, motors).

The Software: Introduce the Arduino IDE. Explain that we use “sketches” (code) to tell the brain what to do.

Key Terminology:

Digital: Only two states—ON (High) or OFF (Low).

Analog: A range of values (e.g., 0 to 1023) used for measuring “how much” moisture is in the soil.

Safety First: Explain why we use resistors (to prevent the LED from “blowing up” from too much current).

Polarity: Teach students that LEDs have a long leg (Positive/Anode) and a short leg (Negative/Cathode).

The Code: Introduce the Blink sketch.

void setup() {

 pinMode(13, OUTPUT);

}

void loop() {

 digitalWrite(13, HIGH); // Turn LED on

 delay(1000);      // Wait 1 second

 digitalWrite(13, LOW); // Turn LED off

 delay(1000);

}

Activity: Students must successfully make their LED blink before moving to the main project.

1. The Hardware Setup

Students will now expand their circuit to include:

• The Sensor: A Capacitive Soil Moisture Sensor (v1.2). Unlike resistive sensors, these don’t corrode as quickly.

• Two LEDs: Green (Moist) and Red (Dry).

• Wiring Guide: Sensor: VCC to 5V, GND to GND, and AUOUT to Analog Pin A0. LEDs: Green to Digital Pin 2, Red to Digital Pin 3 (using resistors for both).

2. The Logic (Programming)

Explain the if/else logic: If the soil is dry, then turn on the Red LED. Otherwise, turn on the Green LED.

const int sensorPin = A0;

const int redLED = 3; 

const int greenLED = 2;

void setup() {

Serial.begin(9600);

 pinMode(redLED, OUTPUT);

 pinMode(greenLED, OUTPUT);

}

void loop() {

int sensorVal = analogRead(A0);

Serial.println(sensorVal);

if( sensorVal > 450) {

   digitalWrite(redLED, HIGH);

  digitalWrite(greenLED, LOW);

}

else{

   digitalWrite(redLED, LOW);

  digitalWrite(greenLED, HIGH);

}

}