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ADS7128 - 8-channel 12-bit ADC and GPIO expander - I2C - STEMMA QT / Qwiic - Adafruit 6494
A 12-bit analog-to-digital converter and GPIO expander: you can set each of the 8 pins of the ADS7128 chip on the module as an analog input, a digital input or a digital output.
- 8 ADC or GPIO pins, sampling up to 140 ksps
- RMS value and zero-crossing detection
- STEMMA QT / Qwiic connectors, 3.3 V or 5 V logic
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8 pins: analog input or digital I/O
The Adafruit ADS7128 combines a 12-bit ADC and a GPIO expander: you can set each of the 8 pins separately as an analog input, a digital input or a digital output. The module works with 3.3 V or 5 V power and logic and communicates over I2C at speeds up to 3.4 MHz.
You connect the STEMMA QT connectors, 4-pin I2C connectors compatible with Qwiic, without soldering, and the Arduino and CircuitPython libraries also work on a Raspberry Pi computer.
ADS7128 module with A0-A7 pins and two STEMMA QT connectors
12 bit
ADC resolution
8
ADC or GPIO pins
140 ksps
max. sampling rate
3.4 MHz
max. I2C bus speed
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ADS7128 board from the top: I2C, ALRT, ADDR and power pins
RMS, zero crossings and a threshold alert
The ADS7128 chip calculates the RMS value of the signal on its own as a 16-bit result and detects signal zero crossings on any of the analog inputs. You can set alert thresholds separately for each analog channel, and an event counter rejects short signal glitches.
The ADS7128 chip reports a threshold crossing on the ALRT pin, an open-drain interrupt output. The analog supply AVDD is separate from the digital supply, so after cutting the AVDD jumper on the board the I2C logic can run at 3.3 V and the analog inputs can run at 5 V.
Is it right for you?
A good choice if:
- you need analog inputs and extra digital pins at the same time
- you measure the RMS value or detect signal zero crossings
- your logic runs at 3.3 V and analog sensors need a range up to 5 V
Consider another option if:
- you need 16-bit resolution and programmable gain: choose the ADS1115
Comparison of ADCs with an I2C interface
| ADS7128 | ADS7830 | ADS1115 | |
|---|---|---|---|
| Resolution | 12 bit | 8 bit | 16 bit |
| Channels | 8 | 8 | 4 single-ended or 2 differential |
| Max. sampling rate | 140 ksps | 70 ksps | 860 samples/s |
| Pins as GPIO | yes | - | - |
| Programmable gain | - | - | up to x16 |
| I2C addresses | 0x10, 0x11, 0x17 (jumpers) | - | 0x48 to 0x4B |
| See | this page | ADS7830 | ADS1115 |
A "-" means this information is not given in the manufacturers' materials.
ADS7128 module pinout
| Pin | Function |
|---|---|
| VIN | 3 V to 5 V power, the same as the microcontroller logic level |
| GND | power and logic ground |
| SCL | I2C clock, 3 V to 5 V logic, 10 kΩ pull-up resistor |
| SDA | I2C data, 3 V to 5 V logic, 10 kΩ pull-up resistor |
| A0 to A7 | analog input, digital input or digital output |
| AVDD | ADC reference voltage, connected to VIN by default |
| ADDR | I2C address set by resistors at power-up |
| ALRT | interrupt output, open drain by default |
| 0x11 and 0x17 jumpers | on the underside, change the address from the default 0x10 |
| On LED | green power LED, disabled by the LED jumper |
Fun fact
The platypus of I2C expanders
Adafruit calls the ADS7128 the platypus of the I2C expander world, because it is hard to classify as only an ADC or only a GPIO expander, since it combines both functions.
Frequently asked questions
How many modules on one bus?
Up to 8 modules. The chip has 8 I2C addresses set by resistors on ADDR, and the jumpers set 0x11 or 0x17.
Does it work with Raspberry Pi?
Yes. Adafruit provides Arduino and CircuitPython libraries for the ADS7128, which also work on a Raspberry Pi.
Do the inputs accept 5 V?
Yes, when the AVDD supply is at 5 V. The analog inputs and digital outputs then work at up to 5 V, also with 3.3 V I2C logic after cutting the AVDD jumper on the board.
Kit contents
- 1 x ADS7128 module with ADC and GPIO expander
- 1 x Header strip for soldering
Technical specifications
| Parameter | Value |
|---|---|
| Chip | Texas Instruments ADS7128 |
| Type | 12-bit SAR ADC and GPIO expander |
| Channels | 8: analog input, digital input, push-pull or open-drain output |
| Max. sampling rate | 140 ksps |
| Additional features | 16-bit RMS, zero-crossing detection, alert thresholds with an event counter, averaging filters, CRC |
| Interface | I2C up to 3.4 MHz, STEMMA QT / Qwiic connectors |
| I2C address | 0x10 (0x11, 0x17 jumpers, ADDR pin: 8 addresses) |
| Module power supply | 3 V to 5 V |
| Chip power supply | AVDD 2.35 V to 5.5 V, DVDD 1.65 V to 5.5 V |
| Chip operating temperature | -40 °C to 85 °C |
| Dimensions | 30.5 x 17.8 x 4.7 mm |
| Manufacturer part number | 6494 |
| Manufacturer | Adafruit |
| Weight | 2.1 g |
Useful links
| Name | Value |
|---|---|
| Width | 6 cm |
| Height | 5 cm |
| Depth | 2 cm |
| Weight | 0.02 kg |
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Product information
This product is a component intended for further assembly or prototyping. It is not a finished product within the meaning of the product safety regulations.
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