Electronics & Circuits · Study deck
Sampling Design: Product Scenarios
A doorbell, thermometer, and ECG monitor do not need the same sample rate.
Voltage Vera is your guide for this deck.
After studying this chapter
Learning objectives
You will be able to:
- Explain: Violating this rule causes aliasing, where high-frequency content masquerades as lower frequencies, producing silently corrupted data that looks plausible but is wrong.
- Explain: The Nyquist theorem is the single most important rule for digitizing analog signals: always sample at least twice the highest frequency present.
- Explain: Sampling is like taking photos of a moving object -- take photos too slowly and you miss the action!
- Explain: Scenario: You're designing a smart doorbell that records 5-second audio clips when the button is pressed.
Major section
Start With the Decision
A doorbell, thermometer, and ECG monitor do not need the same sample rate.
- Each product must preserve its fastest useful change without wasting power or storage.
Major section
For Kids: Meet the Sensor Squad!
Sampling is like taking photos of a moving object -- take photos too slowly and you miss the action!
- Temperature Terry was watching a spinning wheel. "I can see it spinning smoothly, going round and round!".
- the microcontroller said, "I cannot watch continuously like you, Sammy.
- I can only take snapshots -- like photographs.
Major section
For Kids: Meet the Sensor Squad! (continued)
But the wheel was spinning 10 times per second!
- In Max's photos, the wheel looked like it was barely moving -- or even going backwards!
- the LED was confused. "That is like when car wheels look like they spin backwards in movies!".
- "Exactly!" said ADC Andy. "That is called ALIASING.
Major section
For Kids: Meet the Sensor Squad! (continued)
Max is not taking photos fast enough, so the fast spinning LOOKS like slow spinning.".
- the battery asked, "How fast does Max need to take photos?".
- Andy did some math. "The wheel spins 10 times per second.
- Blinking slowly is like undersampling -- you miss what is really happening!
Major section
Doorbell Sampling Design
Scenario: You're designing a smart doorbell that records 5-second audio clips when the button is pressed.
- You need to select the ADC sampling rate for the ESP32 and calculate storage requirements.
- Clips stored: 66 clips (fits in 4 MB with margin).
Major section
Deep dive: Adaptive Multi-Channel Sampling
The system must optimize storage/power by adapting sampling rates.
- Ch3: 200 kHz (ESP32 limit = 83 kHz → requires external ADC).
- Ch4: 100 kHz (requires external ADC).
- Ch3: 200,000 × 2 × 86,400 = 34.6 GB/day (exceeds 30-day budget!).
- Variable rate: Ch3 records only at night (bats), Ch2 only at dawn/dusk (birds).
Major section
Key Takeaway
The Nyquist theorem is the single most important rule for digitizing analog signals: always sample at least twice the highest frequency present.
- Violating this rule causes aliasing, where high-frequency content masquerades as lower frequencies, producing silently corrupted data that looks plausible but is wrong.
Deck summary
Key takeaways
A doorbell, thermometer, and ECG monitor do not need the same sample rate.
- Sampling is like taking photos of a moving object -- take photos too slowly and you miss the action!
- But the wheel was spinning 10 times per second!
- Max is not taking photos fast enough, so the fast spinning LOOKS like slow spinning.".
- Scenario: You're designing a smart doorbell that records 5-second audio clips when the button is pressed.
Retrieval practice
Recall check 1 of 2
Voltage Vera says: answer from memory, then check your reasoning.
Q1The doorbell’s uncompressed audio exceeds its flash budget. Why is halving the sample rate a poor fix for the stated input bandwidth?
Show answer
Answer: C The worked example identifies aliasing when the sample rate is reduced without narrowing the signal.
Retrieval practice
Recall check 2 of 2
Voltage Vera says: answer from memory, then check your reasoning.
Q2A home sensor tracks slowly changing room temperature. What supports a slower sampling plan than an audio recorder?
Show answer
Answer: B The temperature example sets sampling from its change rate and measurement purpose.
Q3Place each sampling concept where it lives so you can predict whether a measured frequency is real or aliased.
Show answer
Answer: A Separate source bandwidth, discrete capture, and interpretation so you can test the Nyquist condition and recognize aliasing instead of trusting every spectral peak.
Print reference
Answers
Answer key.
- C · The worked example identifies aliasing when the sample rate is reduced without narrowing the signal.
- B · The temperature example sets sampling from its change rate and measurement purpose.
- A · Separate source bandwidth, discrete capture, and interpretation so you can test the Nyquist condition and recognize aliasing instead of trusting every spectral peak.