Email alerts on sensor thresholds in Raspberry Pi - Step-by-Step Execution

Concept Flow - Email alerts on sensor thresholds

Start Program

↓

Read Sensor Value

↓

Check if Value > Threshold?

No→Wait & Repeat

Yes↓

Send Email Alert

↓

Wait & Repeat

The program reads a sensor value, checks if it passes a set limit, sends an email if it does, then waits before checking again.

Execution Sample

Raspberry Pi

import smtplib
sensor_value = 75
threshold = 70
if sensor_value > threshold:
    send_email_alert()

This code checks if the sensor value is above the threshold and sends an email alert if true.

Execution Table

Step	Action	Sensor Value	Threshold	Condition (Value > Threshold)	Email Sent
1	Read sensor value	75	70	75 > 70 = True	No
2	Check condition	75	70	True	No
3	Send email alert	75	70	True	Yes
4	Wait before next read	75	70	True	Yes
5	Read sensor value again	65	70	65 > 70 = False	No
6	Check condition	65	70	False	No
7	No email sent, wait	65	70	False	No

💡 Program runs continuously; stops only if manually terminated.

Variable Tracker

Variable	Start	After Step 1	After Step 5	Final
sensor_value	None	75	65	65
threshold	70	70	70	70
email_sent	False	False	False	False

Key Moments - 2 Insights

Why does the program send an email only when the sensor value is above the threshold?

Because the condition 'sensor_value > threshold' must be True to trigger sending an email, as shown in execution_table rows 2 and 3.

What happens when the sensor value is below the threshold?

No email is sent and the program waits to read the sensor again, as seen in execution_table rows 5 to 7.

Visual Quiz - 3 Questions

Look at the execution table, at which step is the email alert sent?

A Step 2

B Step 3

C Step 5

D Step 7

💡 Hint

Check the 'Email Sent' column in the execution_table for when it changes to 'Yes'.

At which step does the sensor value fail to exceed the threshold?

A Step 1

B Step 3

C Step 5

D Step 2

💡 Hint

Look at the 'Condition (Value > Threshold)' column for 'False' value.

If the threshold was set to 80, what would happen at step 1?

A No email sent, condition false

B Email would be sent

C Program would crash

D Sensor value would change

💡 Hint

Compare sensor_value 75 with new threshold 80 in the condition column.

Concept Snapshot

Read sensor value continuously
Check if value exceeds threshold
If yes, send email alert
Wait before next reading
Repeat forever

Full Transcript

This program reads a sensor value on a Raspberry Pi and compares it to a set threshold. If the sensor value is higher than the threshold, it sends an email alert. Otherwise, it waits and reads the sensor again. This cycle repeats continuously to monitor sensor data and notify when limits are exceeded.

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