# Adafruit MCP3421 18-Bit ADC
## Overview
The **Adafruit MCP3421 18-Bit ADC** is a simple, inexpensive, and easy to use 18-bit, 240 SPS, single-channel ADC with an I2C interface that can run up to 3.4MHz clock rate. A perfect component whenever you need an ADC that has differential inputs, adjustable gain, and a built-in precision/low-drift reference voltage.
One of the trade-offs with getting 18-bit precision is that the ADC is not going to be very fast: you can configure the chip to do a faster 12-bit conversion at 240 SPS, but at 18-bits it slows down to 3.5 SPS. That's because the way a [sigma-delta ADC](https://en.wikipedia.org/wiki/Delta-sigma_modulation) works, it 'guesses' the analog voltage and uses a comparator to determine whether the input is higher or lower. Each 'guess' takes an extra step, and thus halves the throughput, so 12-bit is 240 SPS, and 14-bit is 1/4 (2-bit) slower, 60 SPS. Ditto 16-bit is 1/4 slower, 15 SPS, and finally 18-bit is 3.75 SPS.
The MCP3421 is already set up for differential inputs, which means that you can read positive or negative differences between the two inputs, **as long as both signals are between 0 and 2.048V**. This means its not going to be great for reading stuff like potentiometers, where you have a single-end reading referenced to ground, and you want to read the full range from 0 to Vcc. It is great, however, for reading sensors like strain gauges, pressure sensors, or thermocouples.
[We have a ready to go Arduino library that makes usage simple](https://github.com/adafruit/Adafruit_MCP3421): select the sample rate / precision you want and one-shot or continuous mode. Then read values over I2C! This sensor has a fixed address, so [you may want to use a multiplexor](https://learn.adafruit.com/adafruit-tca9548a-1-to-8-i2c-multiplexer-breakout) if you want to connect multiple MCP3421's on a single I2C bus.
To get you going fast, we spun up a custom-made PCB in the [**STEMMA QT** form factor](https://www.adafruit.com/?q=stemma%20qt%20sensor "STEMMA QT form factor"), making it easy to interface with. The [STEMMA QT connectors](https://learn.adafruit.com/introducing-adafruit-stemma-qt/what-is-stemma-qt) on either side are compatible with the [SparkFun Qwiic](https://www.sparkfun.com/qwiic) I2C connectors. This allows you to make solderless connections between your development board and the MCP or to chain it with a wide range of other sensors and accessories using a [**compatible cable**](https://www.adafruit.com/?q=stemma%20qt%20cable).
[**QT Cable is not included** , but we have a variety in the shop](https://www.adafruit.com/?q=stemma+qt+cable&sort=BestMatch).
The board comes with a bit of 0.1" standard header in case you want to use it with a breadboard or perfboard. There are four mounting holes for easy attachment.
- [Next Page](https://learn.adafruit.com/adafruit-mcp3421-18-bit-adc/pinouts.md)
## Primary Products
### Adafruit MCP3421 18-Bit ADC - STEMMA QT / Qwiic
[Adafruit MCP3421 18-Bit ADC - STEMMA QT / Qwiic](https://www.adafruit.com/product/5870)
The **Adafruit MCP3421 18-Bit ADC** is a simple, inexpensive, and easy to use 18-bit, 240 SPS, single-channel ADC with an I2C interface that can run up to 3.4MHz clock rate. A perfect component whenever you need an ADC that has differential inputs, adjustable gain,...
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[Related Guides to the Product](https://learn.adafruit.com/products/5870/guides)
## Featured Products
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[Thermocouple Type-K Glass Braid Insulated Stainless Steel Tip](https://www.adafruit.com/product/3245)
Thermocouples are best used for measuring temperatures that can go above 100°C. This is a bare wires stainless-steel tip probe which can measure air or surface temperatures. Most inexpensive thermocouples have a vinyl covering which can melt at around 200°C, this one uses a fiberglass...
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### STEMMA QT / Qwiic JST SH 4-pin Cable - 100mm Long
[STEMMA QT / Qwiic JST SH 4-pin Cable - 100mm Long](https://www.adafruit.com/product/4210)
This 4-wire cable is a little over 100mm / 4" long and fitted with JST-SH female 4-pin connectors on both ends. Compared with the chunkier JST-PH these are 1mm pitch instead of 2mm, but still have a nice latching feel, while being easy to insert and remove.
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### STEMMA QT / Qwiic JST SH 4-Pin Cable - 50mm Long
[STEMMA QT / Qwiic JST SH 4-Pin Cable - 50mm Long](https://www.adafruit.com/product/4399)
This 4-wire cable is 50mm / 1.9" long and fitted with JST SH female 4-pin connectors on both ends. Compared with the chunkier JST PH these are 1mm pitch instead of 2mm, but still have a nice latching feel, while being easy to insert and remove.
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### STEMMA QT / Qwiic JST SH 4-pin to Premium Male Headers Cable
[STEMMA QT / Qwiic JST SH 4-pin to Premium Male Headers Cable](https://www.adafruit.com/product/4209)
This 4-wire cable is a little over 150mm / 6" long and fitted with JST-SH female 4-pin connectors on one end and premium Dupont male headers on the other. Compared with the chunkier JST-PH these are 1mm pitch instead of 2mm, but still have a nice latching feel, while being easy to insert...
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### STEMMA QT / Qwiic JST SH 4-pin Cable with Premium Female Sockets
[STEMMA QT / Qwiic JST SH 4-pin Cable with Premium Female Sockets](https://www.adafruit.com/product/4397)
This 4-wire cable is a little over 150mm / 6" long and fitted with JST-SH female 4-pin connectors on one end and premium female headers on the other. Compared with the chunkier JST-PH these are 1mm pitch instead of 2mm, but still have a nice latching feel, while being easy to insert and...
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### JST SH 4-pin Cable with Alligator Clips - STEMMA QT / Qwiic
[JST SH 4-pin Cable with Alligator Clips - STEMMA QT / Qwiic](https://www.adafruit.com/product/4398)
This cable will make it super easy to use our plug-and-play STEMMA QT boards with boards like Circuit Playground. On one end you get a Qwiic / STEMMA QT connector (technically known as a JST SH 4-pin plug) into 4 individual wires with grippy alligator clips. We're carrying these to...
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