MCP3421 18-Bit ADC Breakout - STEMMA QT / Qwiic

Jargon buster

Plain-language definitions for the technical terms used above.

ADC

An analogue-to-digital converter reads a changing voltage and turns it into a number the microcontroller can use. It matters when connecting analogue sensors such as light, sound, or variable-resistor sensors.

breakout

A breakout board carries a small or fine-pitched component and brings its connections out to standard, breadboard- and header-friendly pins. Describing a part as a breakout means it can be wired into a project without soldering directly to the component's tiny contacts.

Continuous conversion

A mode where the ADC keeps taking measurements repeatedly at the selected data rate. This is useful when you need a steady stream of sensor readings without starting each measurement manually.

Differential input

A measurement method where the board reads the voltage difference between two input wires instead of measuring one wire compared with ground. This is useful for small sensor signals and noise reduction, but both input voltages still need to stay within the board’s allowed range.

FSR

FSR usually means full-scale range, the total span between the lowest and highest value a converter can output or measure, so error figures quoted as a percentage of FSR depend on the selected range such as 2.5 V or 5 V. In other contexts FSR can instead mean a force-sensing resistor, a component whose resistance changes with applied pressure, so check which sense is meant.

I2C

I2C is a two-wire communication bus used by many sensors and small modules. It matters because several I2C devices can share the same two wires, but each device needs a compatible address and your controller must support I2C.

I2C address

An I2C address is the number a device uses so a microcontroller can tell it apart from other devices on the same I2C bus. It matters because two devices with the same fixed address may conflict if used together.

INL

Integral non-linearity (INL) measures how closely a converter's actual response follows an ideal straight line across its range, and it applies to both DACs and ADCs. Lower INL means conversions are more predictable and accurate, which matters when you need precise analogue control or measurement.

MCP3421

A specific microchip that converts analogue voltages into digital values for a microcontroller to read. Knowing the chip part number helps you find compatible libraries, datasheets, example code, and performance limits for the breakout.

potentiometer

A variable resistor usually turned with a knob or shaft to create an adjustable electrical signal. It is often used for inputs such as volume, brightness or position, so it helps beginners learn how a microcontroller reads changing values.

ppm

ppm means parts per million, a common way to express very small gas concentrations in air. For CO₂ sensors, the ppm range tells you what levels the sensor can measure, such as normal indoor air through to poorly ventilated spaces.

Programmable gain amplifier

A built-in amplifier whose gain can be changed in software to make small input signals easier to measure. This matters because choosing the right gain can improve detail for small sensors, but too much gain can make the input range too small.

Qwiic

Qwiic is a plug-in connector system for I2C devices that uses small 4-pin cables, so you can connect compatible sensors without soldering. It matters because your controller or adapter also needs Qwiic, or you will need a cable or breakout to wire it up.

SPS

SPS means samples per second, the number of measurements an analogue-to-digital converter takes each second. A higher SPS gives faster updates, while on many converters a lower sample rate allows higher-resolution or lower-noise readings.

STEMMA

A plug-and-cable connection system used on some maker electronics boards to make wiring simpler. If a product uses STEMMA, you need the matching cable or connector type to plug it in without soldering.

STEMMA QT

A small plug-in connector system for I2C boards that lets you connect compatible sensors and controllers without soldering. It matters because it can make wiring faster and less error-prone, especially when adding several small modules to a project.

VCC

VCC is the positive power-supply connection on a chip or module. Connecting it to the correct supply voltage is needed for the part to power on and helps avoid damaging the electronics.

voltage reference

A voltage reference is a stable, accurate voltage that a converter uses as its comparison point: an ADC measures its inputs relative to it, while a DAC scales its output to it. A more stable reference gives more consistent results, which matters most in precision sensing and instrumentation.