Automated plant watering system in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this soil moisture check?

Consider this Python code snippet that reads a soil moisture sensor value and decides whether to water the plant.

moisture = 350
if moisture < 300:
    print("Watering plant")
else:
    print("Soil is moist enough")

What will this code print?

Raspberry Pi

moisture = 350
if moisture < 300:
    print("Watering plant")
else:
    print("Soil is moist enough")

A Soil is moist enough

B Error: moisture sensor not found

C No output

D Watering plant

💡 Hint

Think about the condition: is 350 less than 300?

The moisture value is 350, which is not less than 300, so the else block runs, printing "Soil is moist enough".

❓ Predict Output

intermediate

What does this pump control code print?

This code controls a water pump based on a boolean variable pump_on. What is the output?

pump_on = False
if pump_on:
    print("Pump is running")
else:
    print("Pump is off")

Raspberry Pi

pump_on = False
if pump_on:
    print("Pump is running")
else:
    print("Pump is off")

A Pump status unknown

B Pump is running

C Pump is off

D Error: pump_on not defined

💡 Hint

Remember that False means the condition is not true.

Since pump_on is False, the else block runs and prints "Pump is off".

🔧 Debug

advanced

Why does this watering loop run forever?

Look at this code snippet that should water the plant once when soil is dry, but it keeps watering endlessly. What is the cause?

while True:
    moisture = 250
    if moisture < 300:
        print("Watering plant")
    else:
        print("Soil is moist enough")

Raspberry Pi

while True:
    moisture = 250
    if moisture < 300:
        print("Watering plant")
    else:
        print("Soil is moist enough")

A The else block is missing a break statement

B The moisture value never changes inside the loop

C The print statement causes the loop to restart

D The loop condition is wrong, should be while moisture < 300

💡 Hint

Think about what happens to the moisture value each time the loop runs.

The moisture value is always set to 250 inside the loop, so the condition moisture < 300 is always true, causing infinite watering.

📝 Syntax

advanced

Which option has correct syntax to read sensor and water plant?

Choose the code snippet that correctly reads a moisture sensor and waters the plant if dry.

A

moisture = read_sensor()
if moisture < 300:
    water_plant()

B

moisture = read_sensor()
if moisture < 300
    water_plant()

C

moisture = read_sensor()
if moisture < 300:
water_plant()

D

moisture = read_sensor()
if moisture < 300:
    water_plant

💡 Hint

Remember Python needs a colon and indentation for blocks.

Option A has the correct colon after the if statement and indented block for water_plant().

🚀 Application

expert

How many times will the pump run in this code?

This code runs a watering pump based on sensor readings in a list. How many times will it print "Pump running"?

moisture_readings = [320, 280, 290, 310, 270]
pump_runs = 0
for moisture in moisture_readings:
    if moisture < 300:
        print("Pump running")
        pump_runs += 1
print(pump_runs)

Raspberry Pi

moisture_readings = [320, 280, 290, 310, 270]
pump_runs = 0
for moisture in moisture_readings:
    if moisture < 300:
        print("Pump running")
        pump_runs += 1
print(pump_runs)

A 4

B 2

C 5

D 3

💡 Hint

Count how many values in the list are less than 300.

The values 280, 290, and 270 are less than 300, so the pump runs 3 times.

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