Automated plant watering system in Raspberry Pi - Step-by-Step Execution

Concept Flow - Automated plant watering system

Start System

↓

Read Soil Moisture Sensor

↓

Is moisture < threshold?

No→Wait and Read Again

Yes↓

Activate Water Pump

↓

Water for set time

↓

Deactivate Water Pump

↓

Wait before next check

↩Back to Read Soil Moisture Sensor

The system reads soil moisture, checks if watering is needed, waters if dry, then waits before checking again.

Execution Sample

Raspberry Pi

import time
from gpiozero import MCP3008, OutputDevice

sensor = MCP3008(channel=0)
pump = OutputDevice(17)

while True:
    moisture = sensor.value
    if moisture < 0.3:
        pump.on()
        time.sleep(5)
        pump.off()
    time.sleep(10)

This code reads soil moisture and waters the plant for 5 seconds if moisture is below 0.3, then waits 10 seconds before repeating.

Execution Table

Step	Action	Moisture Value	Condition (moisture < 0.3)	Pump State	Wait Time (seconds)
1	Read sensor	0.25	True	Off	0
2	Check condition	0.25	True	Off	0
3	Pump ON	0.25	True	On	5
4	Pump OFF	0.25	True	Off	0
5	Wait before next check	0.25	True	Off	10
6	Read sensor	0.35	False	Off	0
7	Check condition	0.35	False	Off	0
8	Pump remains OFF	0.35	False	Off	0
9	Wait before next check	0.35	False	Off	10
10	Read sensor	0.20	True	Off	0
11	Check condition	0.20	True	Off	0
12	Pump ON	0.20	True	On	5
13	Pump OFF	0.20	True	Off	0
14	Wait before next check	0.20	True	Off	10

💡 Loop continues indefinitely; this trace shows two watering cycles and one skip.

Variable Tracker

Variable	Start	After Step 1	After Step 6	After Step 10	Final
moisture	N/A	0.25	0.35	0.20	0.20
pump state	Off	Off	Off	Off	Off

Key Moments - 3 Insights

Why does the pump turn on only when moisture is below 0.3?

Because the condition in the execution_table at steps 2, 7, and 11 checks if moisture < 0.3; only when True does the pump activate.

What happens if the moisture is above 0.3?

At step 7 and 8, the condition is False, so the pump stays off and the system waits before checking again.

Why is there a wait time after watering or skipping watering?

The wait time (steps 5, 9, 14) prevents the system from checking too frequently, giving time for soil moisture to change.

Visual Quiz - 3 Questions

Look at the execution_table, what is the pump state at step 8?

A Off

B On

C Turning On

D Unknown

💡 Hint

Check the 'Pump State' column at step 8 in the execution_table.

At which step does the system decide not to water the plant?

A Step 2

B Step 7

C Step 11

D Step 3

💡 Hint

Look at the 'Condition' column in the execution_table where it is False.

If the moisture threshold changed to 0.4, how would the pump behavior change at step 6?

A Pump would remain OFF

B Pump would turn ON only after waiting

C Pump would turn ON

D No change

💡 Hint

Compare moisture value at step 6 with new threshold 0.4 in the execution_table.

Concept Snapshot

Automated Plant Watering System:
- Read soil moisture sensor value
- If moisture < threshold (e.g., 0.3), turn pump ON
- Water for fixed time (e.g., 5 seconds)
- Turn pump OFF
- Wait before next sensor reading
- Repeat indefinitely

Full Transcript

This automated plant watering system uses a soil moisture sensor connected to a Raspberry Pi. The program continuously reads the moisture level. If the moisture is below a set threshold (0.3), it activates a water pump for 5 seconds to water the plant. After watering, the pump turns off and the system waits 10 seconds before checking again. If the moisture is above the threshold, the pump stays off and the system waits before the next check. This cycle repeats indefinitely to keep the plant properly watered without overwatering.

Practice

1.

What is the main purpose of an automated plant watering system using a Raspberry Pi?

easy

A. To control room temperature automatically

B. To water plants continuously without checking soil

C. To measure sunlight for plants

D. To water plants only when the soil is dry

Solution

1. Step 1: Understand the system goal

   The system uses sensors to check soil moisture.

2. Step 2: Identify the watering condition

   It waters plants only when soil is dry to save water.

3. Final Answer:

   To water plants only when the soil is dry -> Option D

4. Quick Check:

   Water only if dry = A [OK]

Hint: Focus on saving water by watering only when needed [OK]

Common Mistakes:

• Thinking it waters plants all the time
• Confusing soil moisture with sunlight
• Assuming it controls temperature

2.

Which of the following Python code snippets correctly sets up a GPIO pin 17 as an output to control a water pump?

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
# What goes here?

easy

A. GPIO.setup(17, GPIO.OUT)

B. GPIO.setup(17, GPIO.IN)

C. GPIO.output(17, GPIO.IN)

D. GPIO.output(17, GPIO.OUT)

Solution

1. Step 1: Identify pin mode setup

   GPIO.setup(pin_number, GPIO.OUT) sets pin as output.

2. Step 2: Choose correct function and mode

   GPIO.setup(17, GPIO.OUT) correctly sets pin 17 as output.

3. Final Answer:

   GPIO.setup(17, GPIO.OUT) -> Option A

4. Quick Check:

   Setup output pin = A [OK]

Hint: Use GPIO.setup(pin, GPIO.OUT) to set output pins [OK]

Common Mistakes:

• Using GPIO.IN instead of GPIO.OUT for output pins
• Calling GPIO.output instead of GPIO.setup to set mode
• Confusing pin numbers or modes

3.

What will be the output of this Python code controlling a pump based on soil moisture sensor reading?

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.OUT)
soil_moisture = 300  # sensor value
if soil_moisture < 400:
    GPIO.output(17, GPIO.HIGH)
    print("Pump ON")
else:
    GPIO.output(17, GPIO.LOW)
    print("Pump OFF")

medium

A. SyntaxError

B. Pump OFF

C. Pump ON

D. No output

Solution

1. Step 1: Check soil moisture condition

   Value 300 is less than 400, so condition is true.

2. Step 2: Determine pump action and output

   GPIO.output sets pin HIGH and prints "Pump ON".

3. Final Answer:

   Pump ON -> Option C

4. Quick Check:

   300 < 400 triggers Pump ON [OK]

Hint: Compare sensor value to threshold to decide pump state [OK]

Common Mistakes:

• Misreading the comparison operator
• Confusing HIGH and LOW states
• Ignoring print output

4.

Identify the error in this Raspberry Pi watering system code snippet:

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.OUT)
soil_moisture = 500
if soil_moisture > 400
    GPIO.output(17, GPIO.LOW)
    print("Pump OFF")

medium

A. soil_moisture value is invalid

B. Missing colon (:) after if condition

C. GPIO.output should be GPIO.setup

D. Wrong GPIO pin number

Solution

1. Step 1: Check if statement syntax

   Python requires a colon (:) after the if condition.

2. Step 2: Identify missing colon error

   The code misses ':' after 'if soil_moisture > 400', causing syntax error.

3. Final Answer:

   Missing colon (:) after if condition -> Option B

4. Quick Check:

   if statement needs ':' = D [OK]

Hint: Always put ':' after if conditions in Python [OK]

Common Mistakes:

• Forgetting colon after if
• Confusing GPIO.output with GPIO.setup
• Assuming pin number is wrong

5.

You want to improve the watering system to water plants only if soil moisture is below 400 and only between 6 AM and 8 AM. Which Python code snippet correctly adds this time condition?

import datetime
now = datetime.datetime.now()
soil_moisture = 350
if soil_moisture < 400 and ???:
    print("Watering plants")
else:
    print("No watering")

hard

A. now.hour >= 6 and now.hour <= 8

B. now.hour > 6 or now.hour < 8

C. now.hour < 6 and now.hour > 8

D. now.hour == 6 or now.hour == 8

Solution

1. Step 1: Understand time range condition

   We want hours from 6 to 8 inclusive, so hour >= 6 and hour <= 8.

2. Step 2: Combine soil moisture and time conditions

   Use 'and' to check both soil moisture and time range.

3. Final Answer:

   now.hour >= 6 and now.hour <= 8 -> Option A

4. Quick Check:

   Check hour between 6 and 8 = B [OK]

Hint: Use 'and' with hour >= 6 and <= 8 for time range [OK]

Common Mistakes:

• Using 'or' instead of 'and' for time range
• Using strict inequalities excluding 6 or 8
• Checking only exact hours 6 or 8