Mr. Integral
Embedded notes/Moving and Processing Data/Analog Signals and Conversion

UNIT 11 · MOVING AND PROCESSING DATA

Analog Signals and Conversion

Turn voltages into numbers, and numbers back into voltages.

6 lessons24 guided experiments35 min full read

Temperature, light, current, sound and position all reach firmware as voltages, and an analog-to-digital converter turns them into numbers at chosen instants. Each step can quietly lose information: a signal sampled too slowly turns into a different one, a 12-bit converter delivers fewer than 12 useful bits, a high-impedance sensor leaves the sample capacitor half charged, and a software-timed loop smears the timing. The same care applies on the way out, when PWM or a DAC turns numbers back into voltages.

Start with lesson 1 →
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∫ MR-INTEGRAL · 15 UNITS01Pins · signals and circuits036 lessonsCPU coreand memory026 lessonsRegistersC close to the metal096 lessonsInterruptcontroller136 lessonsSchedulertasks and deadlines046 lessonsFlash imagebuilt by the toolchain156 lessonsSecure bootupdates and keys056 lessonsBoot ROMand reset066 lessonsDebug portprobe, trace146 lessonsPowersleep, brown-out126 lessonsDMA076 lessonsGPIOpins in and out086 lessonsClocksand timers106 lessonsUART · SPI · I²Cserial links116 lessonsADC · DACanalog

The unit in six ideas

  1. 1A sampled signal is described completely only if it contains nothing above the Nyquist frequency f_s / 2.
  2. 21 LSB = Vref / 2^N; code = ⌊Vin / Vref × 2^N⌋, limited to 2^N − 1.
  3. 3Every code is a fraction of Vref: reference errors are gain errors in every reading.
  4. 4Start conversions from a timer or run the ADC free; software-timed sampling carries all the code’s jitter.
  5. 5A moving average of N reduces random noise by √N and delays a step by (N − 1)/2 samples.
  6. 6Filtered PWM gives D × V_supply plus ripple ≈ V_supply D(1 − D) T / τ for T ≪ τ.

Lessons

  1. LESSON 01 · 4 EXPERIMENTS · 6 MIN

    Sampling, Aliasing, and Bandwidth

    How can an ADC report a frequency that is not there, and how do you stop it?

  2. LESSON 02 · 4 EXPERIMENTS · 6 MIN

    Resolution, Quantization, and Accuracy

    What does “12 bits” actually promise?

  3. LESSON 03 · 4 EXPERIMENTS · 6 MIN

    References, Input Impedance, and Acquisition Time

    What are the ADC’s reference and input really doing?

  4. LESSON 04 · 4 EXPERIMENTS · 5 MIN

    Triggered Sampling and Conversion Sequences

    Getting samples at the right moments and out of the ADC in time: software-started, free-running and timer-triggered conversions, why sampling-time jitter limits accuracy, sequences and round-robin scans over several inputs and the skew between them, and collecting results through FIFOs, interrupts and DMA without overruns.

  5. LESSON 05 · 4 EXPERIMENTS · 6 MIN

    Digital Filtering and Sensor Calibration

    How do you tell them apart, and fix each?

  6. LESSON 06 · 4 EXPERIMENTS · 6 MIN

    Analog Outputs and PWM Filtering

    Where is the balance?