# Analog-to-digital conversion

How a voltage becomes a number: resolution, reference voltage, sampling rate and the Nyquist limit.

Page: https://dharanova.com/learn/adc-basics · Track: Sense · Level: Foundation · Facts last checked 6 October 2026

Read first: [What a sensor actually is](https://dharanova.com/learn/what-is-a-sensor.md)

Diagram: Chart, not to scale: an analog voltage between 0 and Vref, sampled at regular points, and the stepped readings each sample is rounded to; one step is marked 1 LSB. Below: one step equals Vref divided by 2 to the N, about 0.8 mV for a 12-bit converter with a 3.3 V reference. Sample at more than twice the signal's highest frequency (Nyquist–Shannon). Effective number of bits (ENOB) counts noise and distortion and is lower than the nominal resolution. SAR converters are the usual ADC in microcontrollers; delta-sigma converters trade speed for high resolution and suit weighing and temperature.

## Key points

1. An N-bit ADC divides its reference voltage into 2^N steps, so one step (1 LSB) is Vref / 2^N: about 0.8 mV for a 12-bit converter with a 3.3 V reference. [1]
2. To capture a signal without aliasing, it must be sampled at more than twice its highest frequency component (the Nyquist–Shannon criterion). [2][3]
3. Effective number of bits (ENOB) expresses real-world performance including noise and distortion, and is lower than the nominal resolution. [4]
4. The ADCs built into microcontrollers are typically SAR (successive-approximation) converters; delta-sigma converters trade speed for high resolution and suit slow, precise signals such as weighing and temperature. [5][1][6][7]

## Common mistakes

- Using a noisy power rail as the ADC reference, then blaming the sensor for the noise.

## Where to go next

- [Uncalibrated bench characterisation of low-cost turbidity, TDS, pH and level sensors on Arduino Uno R4 WiFi](https://dharanova.com/whitepapers/uncalibrated-water-sensors-arduino-uno-r4-wifi.md): a whitepaper from our lab
- [Accuracy, precision and resolution](https://dharanova.com/learn/accuracy-precision-resolution.md): Accuracy, precision and resolution mean different things, and datasheets often blur them. Mixing them up gives readings that look precise but are wrong.
- [Signal conditioning](https://dharanova.com/learn/signal-conditioning.md): Raw sensor signals are often tiny or noisy. Conditioning amplifies and filters them so the ADC can measure them well.
- [The common sensor families](https://dharanova.com/learn/sensor-families.md): How common sensors for temperature, motion and sound work, and what limits each one.

## Sources

1. [A Basic Guide to Bridge Measurements (SBAA532A)](https://www.ti.com/lit/an/sbaa532a/sbaa532a.pdf), Texas Instruments
2. [Communication in the Presence of Noise (Shannon, Proc. IRE, 1949)](https://ieeexplore.ieee.org/document/1697831), IEEE
3. [TI Precision Labs: Aliasing and Anti-aliasing Filters (TIPL 4304) slides](https://www.ti.com/content/dam/videos/external-videos/en-us/2/3816841626001/5831231183001.mp4/subassets/adcs-aliasing-and-anti-aliasing-filters-presentation-quiz.pdf), Texas Instruments
4. [Oversampling the ADC12 for Higher Resolution (SLAA323A)](https://www.ti.com/lit/an/slaa323a/slaa323a.pdf), Texas Instruments
5. [TI Precision Labs: SAR and Delta-Sigma ADCs, Understanding Basic Operation (TIPL 4010) slides](https://www.ti.com/content/dam/videos/external-videos/en-us/7/3816841626001/6228191712001.mp4/subassets/adcs-sar-delta-sigma-basic-operation-presentation.pdf), Texas Instruments
6. [RP2350 datasheet](https://datasheets.raspberrypi.com/rp2350/rp2350-datasheet.pdf), Raspberry Pi
7. [ESP-IDF: Analog to Digital Converter (ADC)](https://docs.espressif.com/projects/esp-idf/en/stable/esp32/api-reference/peripherals/adc/index.html), Espressif Systems