Electronics & Circuits · Study deck
Analog vs. Digital Signals
Picture a water tank sensor that produces a changing voltage while a controller decides when to stop a pump.
Voltage Vera is your guide for this deck.
After studying this chapter
Learning objectives
You will be able to:
- Explain the difference between analog and digital signals and why conversion between them is necessary in IoT systems
- Apply the Nyquist-Shannon sampling theorem to determine appropriate sampling rates for real-world sensor signals
- Calculate ADC/DAC conversion values using standard formulas for temperature, distance, and motor control applications
- Compare PWM and true DAC output methods and select the appropriate technique for a given actuator control scenario
Major section
Start Simple
A neat number on a screen can still be wrong if the input range, output drive, or timing does not match the real circuit.
- The next shows a neat display that leaves the true tank state in doubt.
- The last compares low, middle, and full levels and asks what to do with noise, a lost sensor, and restart.
- A microcontroller means the small computer on the board.
- A digital-to-analog converter (DAC) means a circuit that turns a number into a voltage or current.
Major section
Start Simple (continued)
An analog-to-digital converter means a circuit that turns a voltage into a number; it is called an ADC.
- Pulse-width modulation means control made by changing how long a signal stays on; it is called PWM.
- An actuator means a part that creates a physical action.
- This runway does not choose component values or prove electrical safety.
Major section
In 60 Seconds
Analog-to-digital conversion is the essential bridge between continuous real-world sensor signals and discrete digital microcontrollers.
- This series covers binary number systems, ADC/DAC operation, Nyquist sampling theory, and practical worked examples -- everything you need to understand how IoT devices read sensors and control actuators at the hardware level.
Major section
Overview
Every IoT device that reads a sensor or drives an actuator must cross the analog-digital boundary.
- This five-chapter sequence takes you from binary representation, to ADC behavior, to sampling constraints, to output generation, and finally to worked design calculations.
- The goal is to help you choose the right converter settings and verify whether an interface is precise enough for the job.
Major section
For Kids: Meet the Sensor Squad!
Analog and digital are like the difference between a slide (smooth) and stairs (steps)!: Temperature Terry feels temperatures that go smoothly from cold to hot - like 20.1, 20.2, 20.3 degrees.
- The more steps Andy uses, the more precise the translation becomes.
Major section
Learning Path
The worked-examples chapter belongs at the end because it assumes you already understand binary representation, ADC limits, Nyquist sampling, and DAC/PWM output.
- Quick Reference: If you already know the theory, jump directly to Worked Examples and return to the earlier chapters only when a formula or design choice is unclear.
Major section
Putting Numbers to It
The 12-bit ADC provides 4× better temperature resolution -- crucial for precision applications like laboratory environmental monitoring or medical devices where 0.1°C accuracy is required.
- In practice, use 5× oversampling: fsample=300 Hz to avoid aliasing from harmonics.
Major section
Phoebe's Field Notes: Why Bits and Samples Set the Limit
For this chapter's 5 kHz vibration limit, 12.5 kHz sampling gives a 6.25 kHz Nyquist boundary and 2.50 samples per fastest cycle.
- A 12-bit, 3.3 V ADC has 0.806 mV bins, 0.233 mV rms ideal quantisation noise, and 74.0 dB ideal SNR.
Major section
Key Concepts Summary
Formula: levels = 2^n: Nyquist rate: The minimum safe sampling rate is at least twice the highest signal frequency.
- Rule of thumb: about +/- 0.5 LSB: PWM: A digital signal can behave like an analog output when the load responds to the average duty cycle.
Major section
ADC Design for Vibration
Decision: A 12-bit ideal 3.3 V converter has 3.3 V / 4096 ≈ 0.806 mV per code, coarser than the ADXL1002's ≈0.264 mV change per 0.01 g at 3.3 V.
- Binary (Ch1):: ADC output is binary number requiring correct interpretation.
- PWM (Ch5):: LED dimming via PWM provides visual feedback without true DAC.
- The ESP32 ADC's actual transfer depends on attenuation and calibration; ±0.01 g accuracy is not established without a validated signal chain.
Major section
ADC/DAC Concept Map
Binary (Ch1) -> Digital representation: Requires number systems and base-2 thinking.
- Bits and resolution -> Precision limits: Requires binary and powers of two.
- ADC (Ch2) -> Sensor digitization: Requires both binary and voltage concepts.
- Quantization -> Measurement error: Requires understanding resolution and step size.
- Applied when checking whether a sensor system is accurate enough for its job.
Major section
ADC/DAC Concept Map (continued)
Sampling rate (Ch3) -> Signal capture: Requires Nyquist theorem and frequency concepts.
- Aliasing -> Signal corruption: Requires sampling and frequency understanding.
- DAC (Ch5) -> Analog output: Requires binary and voltage conversion.
- PWM (Ch5) -> Pseudo-analog output: Requires duty-cycle and frequency understanding.
- SPI/I2C -> ADC communication: Requires digital protocol basics.
Major section
Digital Logic in Analog Circuits
Long wire lengths, capacitive loads, and inductive coupling that are acceptable in low-speed digital circuits destroy the performance of analog signal chains.
- Analog signal traces must be kept short (<5 cm where possible), isolated from digital traces, and guarded with ground pour to minimize capacitive coupling.
Major section
3.3V and 5V Logic Mismatch
GPIO outputs from 3.3 V microcontrollers (ESP32, STM32) do not reliably drive 5 V logic inputs that require VIH > 3.5 V.
- Conversely, 5 V outputs connected to 3.3 V inputs can permanently damage 3.3 V ICs.
Deck summary
Key takeaways
A neat number on a screen can still be wrong if the input range, output drive, or timing does not match the real circuit.
- An analog-to-digital converter means a circuit that turns a voltage into a number; it is called an ADC.
- Analog-to-digital conversion is the essential bridge between continuous real-world sensor signals and discrete digital microcontrollers.
- Every IoT device that reads a sensor or drives an actuator must cross the analog-digital boundary.
- The worked-examples chapter belongs at the end because it assumes you already understand binary representation, ADC limits, Nyquist sampling, and DAC/PWM output.
Retrieval practice
Recall check
Voltage Vera says: answer from memory, then check your reasoning.
Q1A 12-bit ADC has how many possible output values?
Show answer
Answer: D The number of output levels for an ADC is 2^n, where n is the number of bits.
Q2For a signal reaching 1 kHz, what is the twice-bandwidth Nyquist boundary rate before practical filter margin?
Show answer
Answer: C Twice the 1 kHz signal frequency gives a 2,000 Hz Nyquist boundary.
Q3What samples and quantizes an analog sensor voltage into digital codes?
Show answer
Answer: C The ADC samples and quantizes the analog sensor voltage into codes.
Print reference
Answers
Answer key.
- D · The number of output levels for an ADC is 2^n, where n is the number of bits.
- C · Twice the 1 kHz signal frequency gives a 2,000 Hz Nyquist boundary.
- C · The ADC samples and quantizes the analog sensor voltage into codes.