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 is a small circuit board that makes a tiny or hard-to-solder component easier to connect to with standard pins. It matters because this OLED module can be wired into a microcontroller project without needing to solder directly to the display’s fine 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

Full-scale range is the span between the lowest and highest output a converter can produce. Error specifications given as a percentage of FSR depend on the selected output range, such as 2.5 V or 5 V.

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 is a measure of how closely a DAC’s output follows an ideal straight-line response across its range. Lower INL means the output voltage is more predictable when you need accurate analogue control.

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

Samples per second, meaning how many measurements the converter can make each second. Higher SPS gives faster updates, while lower SPS on this board allows higher-resolution 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.

voltage reference

A stable voltage the ADC compares inputs against when converting them to numbers. A more stable reference helps produce more consistent measurements, especially in precision sensing and instrumentation.