ADC & DAC — turning signals into numbers

In one line

An analog-to-digital converter (ADC) measures a continuous voltage many times a second and turns each into a number. A DAC does the reverse. The ADC is the doorway every biosignal walks through to become data.

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The two knobs that decide quality

• Sampling rate (Hz) — the Nyquist rule: sample at more than twice the signal's highest frequency, or fast features fold into false junk (aliasing). An ECG is sampled at ~250–1000 Hz.
• Resolution (bits) — 8-bit = 256 steps; 12-bit = 4096; 24-bit (ECG/EEG) resolves microvolts.

Where it shows up in digital health

• Every measured vital — the sensor → amplifier → ADC chain inside an ECG, pulse oximeter or CGM. Its numbers become FHIR Observations.
• DACs drive outputs: alarm tones, stimulator waveforms, actuator drive signals.

Watch for

An anti-aliasing filter before the ADC is mandatory — it removes frequencies above half the sampling rate so they can't alias. Skipping it is a classic source of corrupted readings.