Qwiic MUX Hookup Guide
Englandsaurus Introduction
The Qwiic Mux - TCA9548A enables communication with multiple I2C devices that have the same address. The IC is simple to interface with and also has 8 configurable addresses of its own, this allows you to put 64 I2C buses on a single bus!
In this tutorial we’ll go over how to talk to sensors on different channels of your MUX. The application of this is pretty straightforward so things won’t get too fancy.
Required Materials
To get started, you’ll need a microcontroller to, well, control everything.
Now to get into the Qwiic ecosystem, the key will be one of the following Qwiic shields to match your preference of microcontroller:
You will also need a Qwiic cable to connect the shield to your MUX, choose a length that suits your needs.
Tools
Depending on your setup, you may need a soldering iron, solder, and general soldering accessories.
Suggested Reading
If you aren’t familiar with our new Qwiic system, we recommend reading here for an overview. We would also recommend taking a look at the following tutorials if you aren’t familiar with them.
Qwiic Shield for Arduino & Photon Hookup Guide
Hardware Overview
Let’s look over a few characteristics of the TCA9548A so we know a bit more about how it behaves.
| Characteristic | Range |
|---|---|
| Operating Voltage | 1.65V - 5.5V |
| Operating Temperature | -40 - 85° C |
| I2C Address | 0x70 (default) up to 0x77 (see below table) |
The Qwiic input for the Mux is located at the top-center of the board, labeled Main, highlighted in the image below. The outputs are then located on the left and right sides of the board and are numbered accordingly.
The onboard reset pin, highlighted below, is an active low input. Pulling reset low for at least 6 ns will restart the multiplexer.
The Qwiic Mux also allows you to change the last 3 bits of the address byte, allowing for 8 jumper selectable addresses if you happen to need to put more than one Mux on the same I2C port. The address can be changed by adding solder to any of the three ADR jumpers, shown in the image below.
The below table shows which jumpers must be soldered together to change to the corresponding address.
| I2C Address | ADR2 | ADR1 | ADR0 |
|---|---|---|---|
| 0x70 | Open | Open | Open |
| 0x71 | Open | Open | Closed |
| 0x72 | Open | Closed | Open |
| 0x73 | Open | Closed | Closed |
| 0x74 | Closed | Open | Open |
| 0x75 | Closed | Open | Closed |
| 0x76 | Closed | Closed | Open |
| 0x77 | Closed | Closed | Closed |
If you want to remove the pullup resistors from the I2C bus, simply remove the solder from the jumper highlighted in the below image.
Hardware Assembly
If you haven’t yet assembled your Qwiic Shield, now would be the time to head on over to that tutorial.
Qwiic Shield for Arduino Photon Hookup Guide
With the shield assembled, SparkFun’s new Qwiic environment means that connecting the mux could not be easier. Just plug one end of the Qwiic cable into the Qwiic multiplexer breakout, the other into the Qwiic Shield of your choice and you’ll be ready to upload a sketch and figure out just how all those address sharing sensors are behaving. It seems like it’s too easy to use, but that’s why we made it that way!
Example Code
Note: This example assumes you are using the latest version of the Arduino IDE on your desktop. If this is your first time using Arduino, please review our tutorial on installing the Arduino IDE. If you have not previously installed an Arduino library, please check out our installation guide.
SparkFun has written some example code to enable and disable ports on the Qwiic Mux. Go ahead and download this example code here.
Additionally, you will need to install the MMA8452Q Arduino library if you are using two MMA8452Q accelerometers. First, you’ll need the Sparkfun MMA8452Q Arduino library. You can obtain these libraries through the Arduino Library Manager. Search for Sparkfun MMA8452Q Accelerometer by Jim@SparkFun Electronics to install the latest version. If you prefer downloading the libraries from the GitHub repository and manually installing it, you can grab them here:
Download Sparkfun MMA8452Q Accelerometer (ZIP)
Arduino Example Example1-BasicReadings.ino
Opening Example1-BasicReadings will open two tabs in the Arduino IDE, the first example, and also Mux_Control. Let’s take a look under the hood of Mux_Control to get an idea of what’s going on. There are two functions here, boolean enableMuxPort(byte portNumber) and boolean disableMuxPort(byte portNumber) which is pretty much all we need to specify which channels we’d like to talk to on the Mux. If we have a sensor on channel 0, we simply call enableMuxPort(0) to open that channel on the multiplexer. Then we’ll take whatever reads and perform whatever actions we’d like to the sensor on that channel. Once finished, we have to call disableMuxPort(0) to close communication on that channel so we don’t accidentally perform actions on the sensor on that channel. The below example code shows how to read from two MMA8452Q accelerometers.
language:c
#include <Wire.h>
#include <SFE_MMA8452Q.h> //From: https://github.com/sparkfun/SparkFun_MMA8452Q_Arduino_Library
MMA8452Q accel;
#define NUMBER_OF_SENSORS 2
void setup()
{
Serial.begin(9600);
Serial.println("Qwiic Mux Shield Read Example");
Wire.begin();
//Initialize all the sensors
for (byte x = 0 ; x < NUMBER_OF_SENSORS ; x++)
{
enableMuxPort(x); //Tell mux to connect to port X
accel.init(); //Init the sensor connected to this port
disableMuxPort(x);
}
Serial.println("Mux Shield online");
}
void loop()
{
for (byte x = 0 ; x < NUMBER_OF_SENSORS ; x++)
{
enableMuxPort(x); //Tell mux to connect to this port, and this port only
if (accel.available())
{
accel.read();
Serial.print("Accel ");
Serial.print(x);
Serial.print(": ");
Serial.print(accel.cx, 2);
Serial.print(" ");
Serial.print(accel.cy, 2);
Serial.print(" ");
Serial.print(accel.cz, 2);
Serial.print(" ");
Serial.println(); // Print new line every time.
}
disableMuxPort(x); //Tell mux to disconnect from this port
}
delay(1); //Wait for next reading
}
With the example provided, you should be able to read two I2C sensors with the same address on the same bus! Try opening up the Arduino Serial Monitor set to 9600 baud in order to read the sensor values.
Resources and Going Further
Now that you’ve successfully got your Qwiic mux listening to all of those concurrent addresses, it’s time to incorporate it into your own project!
For more information, check out the resources below:
- Schematic (PDF)
- Eagle Files (ZIP)
- Datasheet
- Qwiic Landing Page
- Example Code
- GitHub Repo
- SparkFun Product Showcase: Qwiic Mux
Need even more inspiration for your next project? Check out some of these related tutorials: