The Adafruit ADS7128 chip offers a unique combination of Analog-to-Digital Converter (ADC) and General Purpose Input/Output (GPIO) expansion capabilities. (Illustrative AI-generated image).
Adafruit ADS7128 ADC GPIO Expander: A Hybrid Chip for I2C Projects
Many electronics projects require both analog sensors and extra digital pins. Traditionally, this meant using separate analog-to-digital converter (ADC) and general-purpose input/output (GPIO) expander boards. This can lead to more complex wiring, increased costs, and a higher component count on the I2C bus. Adafruit’s new ADS7128 breakout board aims to simplify these projects by combining both functionalities into a single, versatile I2C device. The board, announced on June 25, 2026, is built around a Texas Instruments chip that offers eight channels, each configurable as either an analog input or a digital GPIO pin. This hybrid approach is relatively rare in the world of I2C expanders, where most chips specialize in one function or the other. Adafruit has aptly dubbed it the “Platypus” of I2C expanders, highlighting its unique ability to blend two distinct functions into one chip.
For makers and engineers, this means fewer devices to manage, simpler code, and a more compact overall design. The ADS7128 breakout board (product number 6494) uses Adafruit’s STEMMA QT connector, which is compatible with SparkFun’s Qwiic standard. This allows for plug-and-play connectivity with a wide range of microcontrollers without any soldering. The board is designed for users who want to add analog sensing (e.g., potentiometers, light sensors, temperature probes) and digital I/O (e.g., buttons, LEDs, relays) to their projects while minimizing wiring and component count. This article explores the capabilities of the ADS7128, its practical applications for makers, and how to get started with this innovative hybrid chip. We will also discuss its advantages over using separate expansion boards and the broader context of I2C expander solutions in the maker ecosystem.
Understanding the Adafruit ADS7128 Hybrid Chip
The ADS7128 breakout board is built around a Texas Instruments chip, offering eight channels that can be individually set as analog inputs or digital GPIO pins. This means you can connect analog sensors like potentiometers, light sensors, or temperature probes to some channels, while using others to read buttons, control LEDs, or interface with other digital devices. The ability to mix ADC and GPIO on a single chip is a significant innovation. In typical projects, a user might need an ADS1115 (a 4-channel ADC) and an MCP23017 (a 16-channel GPIO expander) to achieve similar functionality. The ADS7128 reduces the component count by combining these into one device, which simplifies PCB layout, reduces power consumption, and lowers overall system cost.
Adafruit has conveniently packaged this chip on a small board featuring a STEMMA QT connector. This connector is compatible with SparkFun’s Qwiic standard, allowing for easy plug-and-play integration with many development boards without the need for soldering. The board’s product number is 6494. The I2C interface is standard, with a configurable address that allows multiple ADS7128 boards to be used on the same bus. The compact size of the breakout board makes it ideal for integration into space-constrained projects, such as wearable devices, sensor nodes, or custom control panels. Adafruit’s announcement on June 25, 2026, did not include full technical specifications such as ADC resolution, sample rate, or GPIO current limits, but based on similar chips in this category, typical resolutions range from 10-bit to 12-bit, with sample rates in the kilohertz range. Once the datasheet becomes available, this article will be updated with precise numbers.
Key Features of the ADS7128 Breakout Board
The Adafruit ADS7128 offers several compelling features for hobbyists and developers:
- 8 Configurable Channels: Each channel can be independently set as an analog input (ADC) or a digital GPIO pin, offering maximum flexibility. You can use as many ADC channels as you need and the remaining channels as GPIO, or vice versa.
- I2C Interface: Utilizes the standard I2C protocol, ensuring compatibility with a wide range of microcontrollers, including Arduino, Raspberry Pi Pico, ESP32, and many others. The I2C address can be changed via a solder jumper or address pin, allowing for multiple boards on the same bus.
- STEMMA QT / Qwiic Connector: Features a 4-pin JST SH connector for power, ground, SDA, and SCL, enabling easy daisy-chaining of multiple devices without soldering. This connector is widely supported in the maker community.
- Compact Size: The small footprint makes it ideal for integration into space-constrained projects. The board measures approximately 25.4mm x 17.8mm (1″ x 0.7″), similar to other Adafruit STEMMA QT breakout boards.
- Configurable I2C Address: Allows for the use of multiple ADS7128 boards on the same I2C bus by changing the address via a solder jumper or address pin. Typically, up to four addresses are available, giving you up to 32 configurable channels in total.
- Solderless Connectivity: Basic use requires no soldering, thanks to the STEMMA QT connector. Simply plug in a compatible cable and connect to your microcontroller. Header pins are also included for those who prefer traditional wiring.
- Hybrid Functionality: The chip’s ability to act as both an ADC and a GPIO expander is its standout feature. This reduces the number of I2C devices needed, freeing up bus addresses and simplifying code.
While Adafruit has not yet released the full datasheet, chips in this category typically offer 10-bit or 12-bit ADC resolution and sample rates in the kilohertz range. The GPIO pins likely support digital input with pull-up resistors and digital output with limited current drive (e.g., 1-5 mA per pin). The exact specifications will be confirmed when official documentation is published. The board also likely includes built-in pull-up resistors on the I2C lines, as is standard on Adafruit breakout boards, to simplify setup.
How the ADS7128 Combines ADC and GPIO
The core innovation of the ADS7128 lies in its channel configurability. Through I2C commands, each of the eight channels can be individually configured to operate as either an analog input (ADC) or a digital GPIO pin. This flexibility is achieved through internal configuration registers that control the mux and signal paths within the chip. When a channel is set to ADC mode, it connects to the internal analog-to-digital converter, which measures the voltage on that pin and reports the digital value over I2C. When set to GPIO mode, the pin can be used as a digital input (reading logic high or low) or a digital output (driving a pin high or low). This dual-mode capability means that a single chip can handle a wide variety of sensor and control tasks.
The I2C interface allows for easy configuration and readout. Typical commands include setting the mode for each channel, reading ADC values, and writing or reading digital states. The chip likely supports continuous conversion mode for ADC channels (where it samples at a fixed rate) and single-shot mode for on-demand readings. For GPIO, the state of all digital pins can be read or written in a single I2C transaction. This simplicity is a major advantage over using separate chips, which would require different protocols and libraries. Adafruit will likely provide an Arduino library and CircuitPython support, making it even easier to integrate the ADS7128 into projects.
One practical implication of this hybrid design is that it allows for more dynamic projects. For example, a prototyping board might use some channels as analog inputs for sensors during development, and later reconfigure those same channels as digital outputs for controlling relays or LEDs when the design is finalized. This adaptability is particularly valuable in educational settings or for rapid prototyping, where requirements may change frequently. The ADS7128 essentially provides a flexible I/O bank that can be reconfigured on the fly, without needing to swap hardware.
Potential Applications for the ADS7128
The hybrid nature of the ADS7128 opens up many application possibilities across different domains. For makers and hobbyists, the board can be used in any project that requires both analog sensing and digital control. Here are a few concrete examples:
- Sensor Hub for IoT Devices: Use a few ADC channels to read temperature, light, or humidity sensors, and use the remaining GPIO pins to control a buzzer, LED, or relay. All of this can be done with a single I2C device connected to an ESP32 or Raspberry Pi Pico.
- Custom Game Controller: Use ADC channels for analog joysticks or potentiometers, and GPIO channels for buttons and LEDs. The ADS7128 can handle both inputs and outputs, reducing wiring complexity compared to using separate components.
- Home Automation: Monitor analog sensors like photoresistors or thermistors and control digital outputs like relays for lights or fans. The compact size allows the board to be placed inside small junction boxes.
- Educational Kits: In classrooms, students can learn about both analog and digital signals using one board. They can experiment with configuring channels differently and see how the system responds.
- Data Logging: Combine analog sensor readings with digital status inputs (e.g., switch positions) and log everything to an SD card or transmit over WiFi. The I2C bus allows for additional sensors to be daisy-chained.
These applications highlight the versatility of the ADS7128. By combining two common functions into one chip, Adafruit has created a product that can simplify many typical maker projects. The STEMMA QT ecosystem also means that the board can be easily integrated with other Adafruit sensors and displays, enabling complex systems with minimal wiring.
Comparison to Traditional Solutions
To appreciate the value of the ADS7128, it is helpful to compare it to the traditional approach of using separate ADC and GPIO expander boards. Common ADC expanders include the ADS1015 (12-bit, 4-channel) and ADS1115 (16-bit, 4-channel), both from Adafruit. Popular GPIO expanders include the MCP23017 (16-bit I/O) and the PCA9685 (PWM controller with I/O capabilities). In a typical project that needs 4 analog inputs and 4 digital I/O pins, one could use an ADS1115 and an MCP23017. This would consume two I2C addresses, require more wiring, and increase cost and board space. The ADS7128, with its 8 configurable channels, can handle this configuration with a single chip, using only one I2C address and taking up less space.
There are trade-offs, however. The ADC resolution and sample rate of the ADS7128 may be lower than dedicated ADCs like the ADS1115, which offers 16-bit resolution. Similarly, the GPIO current drive may be less than robust GPIO expanders like the MCP23017, which can sink up to 25 mA per pin. But for many projects, the flexibility and simplification outweigh these limitations. The ADS7128 is best suited for applications where moderate analog precision (10-12 bits) and basic digital I/O are sufficient. Users who need high-precision analog measurements or high-current digital outputs may still need separate chips. Nonetheless, the ADS7128 fills a gap in the market for a simple, all-in-one I2C expander that can handle both functions.
Another advantage of the ADS7128 is its use of the STEMMA QT / Qwiic connector. This standardized connector allows for daisy-chaining multiple boards without soldering, which is not always possible with other expander boards that rely on header pins. The plug-and-play nature reduces setup time and is especially beneficial in educational environments or for beginners who may not have soldering equipment.
The Platypus of I2C Expanders: Why It Matters
Adafruit’s nickname for the ADS7128 – the “Platypus” of I2C expanders – is fitting. Like the platypus, which is a mammal that lays eggs and has a bill like a duck, the ADS7128 defies conventional categorization. Most I2C expander chips are specialized: they are either purely analog (ADC) or purely digital (GPIO). The ADS7128 crosses this boundary, offering a hybrid solution that can adapt to the needs of the project. This is significant because it reflects a broader trend in the electronics industry toward more integrated, multifunctional components that simplify design and reduce BOM costs.
For the maker community, this means that projects can become more efficient. Instead of searching for a separate ADC and GPIO expander and then writing code for two different chips, a user can now use one device. This also reduces the number of I2C addresses consumed, which is a limited resource on many microcontrollers. On a bus with multiple sensors, every free address counts. The ADS7128’s ability to handle both analog and digital I/O frees up addresses for other sensors, such as accelerometers, displays, or environmental monitors.
Adafruit has a long history of creating breakout boards that make complex chips accessible to hobbyists. The STEMMA QT system is a key part of this strategy, ensuring that new products integrate seamlessly into the existing ecosystem. The ADS7128 is a logical addition to this lineup, offering a unique combination of features that should appeal to both beginners and experienced makers. As of the announcement on June 25, 2026, no pricing or specific availability information has been provided, but interested users can visit the Adafruit blog or product page (product number 6494) for updates.
Getting Started with the ADS7128
While Adafruit has not yet released a full tutorial or library for the ADS7128, the standard approach for similar STEMMA QT boards is straightforward. Users will likely need to connect the board to a microcontroller via a STEMMA QT cable (or use header pins for permanent wiring). Power can be supplied at 3.3V or 5V (check the chip’s voltage range once datasheet is available). The I2C bus will automatically detect the board, and users can communicate with it by sending configuration commands and reading data.
Adafruit typically provides Arduino libraries and CircuitPython drivers for their breakout boards. It is reasonable to expect similar support for the ADS7128. The library would include functions for setting channel modes, reading ADC values, and controlling digital outputs. Example code might demonstrate how to read a potentiometer on one channel and toggle an LED on another channel. Once the library is available, even those with minimal programming experience can leverage the ADS7128’s capabilities.
For advanced users, the chip’s I2C registers can be accessed directly, allowing for custom configurations and optimizations. The ability to reconfigure channels on the fly opens up possibilities for adaptive systems where the I/O roles change based on system state. For instance, during initial calibration, all channels could be analog inputs to read sensor values, and after calibration, some could switch to digital outputs to trigger actuators. This dynamic reconfiguration is a powerful feature that is rare in low-cost I2C expanders.
As more information becomes available, this article will be updated with links to datasheets, tutorials, and library downloads. In the meantime, makers can prepare by stocking up on STEMMA QT cables and thinking about projects that could benefit from the ADS7128’s hybrid nature.
Conclusion
The Adafruit ADS7128 8-Channel ADC and GPIO Expander is a novel product that fills a gap in the I2C expander market. By combining analog-to-digital conversion and digital I/O in a single chip, it offers a flexible and compact solution for a wide range of maker projects. The use of the STEMMA QT / Qwiic connector ensures easy integration with existing development boards and sensors. While specific technical details, pricing, and availability have yet to be announced, the product’s concept is promising. The ADS7128 is particularly well-suited for projects that require a moderate number of both analog inputs and digital I/O pins, where the convenience of a single chip outweighs the need for highest precision or drive strength. As the “Platypus of I2C expanders,” the ADS7128 challenges conventions and offers a new way to think about I/O expansion. Adafruit’s announcement on June 25, 2026, marks the beginning of what could become a popular addition to many makers’ toolkits. Keep an eye on the Adafruit blog and product page for further updates, including datasheets, tutorials, and availability.
