Email alerts on sensor thresholds in Raspberry Pi - Mini Project: Build & Apply

Email alerts on sensor thresholds

📖 Scenario: You have a Raspberry Pi connected to a temperature sensor. You want to monitor the temperature and get an email alert when it goes above a certain limit.

🎯 Goal: Build a simple Python program that reads temperature data, checks if it crosses a threshold, and sends an email alert if it does.

📋 What You'll Learn

Create a dictionary called sensor_data with temperature readings.

Create a variable called threshold with the value 30.

Use a for loop with variables time and temp to iterate over sensor_data.items() and collect times when temperature exceeds the threshold.

Print the list of times when temperature crossed the threshold.

💡 Why This Matters

🌍 Real World

Monitoring sensors on a Raspberry Pi is common in home automation and safety systems. Sending alerts helps users react quickly to important changes.

💼 Career

Understanding how to process sensor data and trigger alerts is useful for roles in IoT development, embedded systems, and automation engineering.

1

Create sensor data dictionary

Create a dictionary called sensor_data with these exact entries: '10:00': 25, '11:00': 28, '12:00': 31, '13:00': 29, '14:00': 35.

Raspberry Pi

# Create the sensor_data dictionary with given time and temperature readings
# Your code here

Hint

Use curly braces {} to create a dictionary with the exact keys and values.

2

Set temperature threshold

Create a variable called threshold and set it to 30.

Raspberry Pi

sensor_data = {'10:00': 25, '11:00': 28, '12:00': 31, '13:00': 29, '14:00': 35}
# Create the threshold variable with value 30
# Your code here

Hint

Just assign the number 30 to the variable named threshold.

3

Find times when temperature exceeds threshold

Create an empty list called alert_times. Use a for loop with variables time and temp to iterate over sensor_data.items(). Inside the loop, if temp is greater than threshold, append time to alert_times.

Raspberry Pi

sensor_data = {'10:00': 25, '11:00': 28, '12:00': 31, '13:00': 29, '14:00': 35}
threshold = 30
# Create alert_times list and add times when temperature > threshold
# Your code here

Hint

Remember to create an empty list first. Then use a for loop with time, temp to check each temperature.

4

Print alert times

Write a print statement to display the alert_times list.

Raspberry Pi

sensor_data = {'10:00': 25, '11:00': 28, '12:00': 31, '13:00': 29, '14:00': 35}
threshold = 30
alert_times = []
for time, temp in sensor_data.items():
    if temp > threshold:
        alert_times.append(time)
# Print the alert_times list
# Your code here

Hint

Use print(alert_times) to show the list of times when temperature was above the threshold.

Practice

1. What is the main purpose of sending email alerts when a sensor value crosses a threshold on a Raspberry Pi?

easy

A. To store sensor data permanently in a database

B. To notify the user immediately about important sensor events

C. To increase the sensor's measurement accuracy

D. To reset the sensor automatically

Solution

1. Step 1: Understand the role of email alerts

   Email alerts are used to inform users instantly when something important happens, like a sensor crossing a limit.

2. Step 2: Compare options with this purpose

   Only To notify the user immediately about important sensor events matches this purpose. Options B, C, and D describe unrelated tasks.

3. Final Answer:

   To notify the user immediately about important sensor events -> Option B

4. Quick Check:

   Email alerts = notify user instantly [OK]

Hint: Email alerts are for instant notifications, not data storage [OK]

Common Mistakes:

• Confusing alerts with data logging
• Thinking alerts improve sensor accuracy
• Assuming alerts reset hardware automatically

2. Which of the following Python code snippets correctly sends an email alert when a sensor value exceeds 50?

easy

A. if sensor_value > 50:
send_email_alert()

B. if sensor_value < 50
send_email_alert()

C. if sensor_value > 50
send_email_alert()

D. if sensor_value > 50:
send_email_alert

Solution

1. Step 1: Check Python if-statement syntax

   Python requires a colon after the if condition and indentation for the block.

2. Step 2: Validate each option

   if sensor_value > 50: send_email_alert() has correct syntax and logic. if sensor_value < 50 send_email_alert() misses colon and wrong condition. if sensor_value > 50 send_email_alert() misses colon and indentation. if sensor_value > 50: send_email_alert misses parentheses for function call.

3. Final Answer:

   if sensor_value > 50: send_email_alert() -> Option A

4. Quick Check:

   Correct if syntax + function call = if sensor_value > 50: send_email_alert() [OK]

Hint: Remember colon and indentation after if, and parentheses for function calls [OK]

Common Mistakes:

• Missing colon after if condition
• Forgetting parentheses when calling functions
• Incorrect indentation causing syntax errors

3. Given the code below, what will be printed if sensor_value = 75?

def check_sensor(value):
    if value > 70:
        print("Alert: High sensor value!")
    else:
        print("Sensor value normal.")

check_sensor(sensor_value)

medium

A. Alert: High sensor value!

B. No output

C. Sensor value normal.

D. SyntaxError

Solution

1. Step 1: Analyze the condition with sensor_value = 75

   Since 75 > 70, the if condition is true.

2. Step 2: Determine which print statement runs

   The code prints "Alert: High sensor value!" because the if condition is met.

3. Final Answer:

   Alert: High sensor value! -> Option A

4. Quick Check:

   75 > 70 triggers alert print [OK]

Hint: Check if condition true or false to find printed message [OK]

Common Mistakes:

• Confusing else output with if output
• Assuming no output if condition true
• Thinking code has syntax errors

4. The following code is intended to send an email alert if the sensor value is above 60, but it does not work. What is the error?

sensor_value = 65
if sensor_value > 60
    send_email_alert()

medium

A. send_email_alert() is not defined

B. Indentation is incorrect

C. sensor_value should be a string

D. Missing colon after the if condition

Solution

1. Step 1: Check syntax of the if statement

   The if statement is missing a colon at the end of the condition line.

2. Step 2: Identify the cause of failure

   Without the colon, Python raises a syntax error and the code won't run.

3. Final Answer:

   Missing colon after the if condition -> Option D

4. Quick Check:

   if statement requires colon [:] [OK]

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

Common Mistakes:

• Forgetting colon after if condition
• Assuming function is undefined without checking syntax first
• Thinking sensor_value must be string

5. You want to send an email alert only once when the sensor value crosses above 80, not repeatedly while it stays above 80. Which approach is best to implement this on a Raspberry Pi?

hard

A. Restart the Raspberry Pi after each alert to reset the sensor

B. Send an email every time the sensor value is checked and above 80

C. Use a flag variable to track if alert was already sent and reset it when value goes below 80

D. Ignore sensor values below 80 and send emails continuously

Solution

1. Step 1: Understand the problem of repeated alerts

   Sending emails repeatedly while the value stays high can spam the user.

2. Step 2: Use a flag to send alert only once

   A flag variable remembers if alert was sent; reset it when value drops below threshold to allow future alerts.

3. Final Answer:

   Use a flag variable to track if alert was already sent and reset it when value goes below 80 -> Option C

4. Quick Check:

   Flag variable prevents repeated alerts [OK]

Hint: Track alert state with a flag to avoid repeated emails [OK]

Common Mistakes:

• Sending emails every check causes spam
• Restarting device is inefficient and unnecessary
• Ignoring values below threshold misses reset opportunity