# Adafruit PCA9546 4-Channel STEMMA QT Multiplexer
## Overview
You just found the perfect I2C sensor, available in a handy chainable [**Qwiic, or STEMMA QT**](https://learn.adafruit.com/introducing-adafruit-stemma-qt) package, and you want to wire up two or three or four of them to your microcontroller when you realize "Uh oh, this chip has a fixed I2C address, and from what I know about I2C, you cannot have two devices with the same address on the same SDA/SCL pins!" Are you out of luck? You would be, if you didn't have this ultra-cool **Adafruit PCA9546** **4 Channel STEMMA QT / Qwiic I2C Multiplexer**!
Finally, a way to get up to 4 same-address I2C devices hooked up to one microcontroller - this multiplexer acts as a gatekeeper, shuttling the commands to the selected I2C port with your command. [If you need to have up to 8 multiplexed devices, check out the 8-channel PCA9548 version of this board.](https://www.adafruit.com/product/5626)
**In case you're wondering why this uses the PCA9546 and not the [TCA9546A](https://www.ti.com/product/TCA9546A)**, the PCA9546 is the 'fraternal twin sister' of the TCA9546 but is easier to get during the great chip shortage of 2022-23. It works exactly the same, just can't go down to 1.8V power which is OK because QT boards are 3V or 5V only anyways. [You can still use any example code or library for the TCA9546 or TCA9548](https://learn.adafruit.com/adafruit-tca9548a-1-to-8-i2c-multiplexer-breakout/overview)
Using it is fairly straight-forward: the multiplexer itself is on I2C address 0x70 (but can be adjusted from 0x70 to 0x77 using jumpers on the back) and you simply write a single byte with the desired multiplexed output number to that port, and bam - any future I2C packets will get sent to that port. In theory, you could have 8 of these multiplexers on each of 0x70-0x77 addresses in order to control 4\*8 = 32 of the same-I2C-addressed-part.
The **Adafruit STEMMA QT / Qwiic PCA9546 Breakout - 4 Channel** has five JST SH 1mm connectors: 1 input and 4 outputs. There's one port at the end that connects to your I2C controller (there are also breadboard breakout pins if you need them). Use this breakout to add as many I2C devices to the bus as you need. Complete with mounting holes so the board can be added to any system. A small power LED lets you know that the hub board has connectivity.
There's even an onboard 3.3V 500mA regulator, so if you're using this with a 5V microcontroller like an Arduino 328-compatible, you can level shift all the QT ports to have 3V power and logic level. Simply cut/solder the jumper on the bottom of the PCB to force the power and logic level to be 3V.
Of course, because [STEMMA QT is Qwiic compatible](https://learn.adafruit.com/introducing-adafruit-stemma-qt), it will [work with any and all STEMMA QT or Qwiic boards and parts we have in the Adafruit shop](https://www.adafruit.com/?q=stemma%20qt).
Comes with only the assembled PCB, no [cables or sensors included (we have tons available though!)](http://learn.adafruit.com/introducing-adafruit-stemma-qt)
# Adafruit PCA9546 4-Channel STEMMA QT Multiplexer
## Pinouts
The default I2C address is **0x70**.
## Power Pins
- **V+** - this is the power pin. Since the multiplexer chip uses 3-5 VDC, to power the board, give it the same power as the logic level of your microcontroller - e.g. for a 5V micro like Arduino, use 5V.
- **-** - common ground for power and logic.
## I2C Logic Pins - Control
- **SCL**** **- I2C clock pin, connect to your microcontroller I2C clock line. This pin is level shifted so you can use 3-5V logic, and there's a ** 10K pullup** on this pin. This connection is shared with the STEMMA QT port on the opposite side of the board.
- **SDA**** **- I2C data pin, connect to your microcontroller I2C data line. This pin is level shifted so you can use 3-5V logic, and there's a ** 10K pullup** on this pin. This connection is shared with the STEMMA QT port on the opposite side of the board.
- **[STEMMA QT](https://learn.adafruit.com/introducing-adafruit-stemma-qt) - **These connectors allow you to connect to dev boards with **STEMMA QT** connectors or to other things with [various associated accessories](https://www.adafruit.com/category/619). There's **one port at the end** that connects to your microcontroller. The other four connectors in two rows of two are discussed below.
## I2C Logic Pins - Multiplexed
- **STEMMA QT Ports 0** to **3** - There are four JST SH 1mm connectors in two rows of two, all with the power, ground, and SDA/SCL pins connected. There are 4 sets of **SDA** and **SCL** pins, from **SD0/SC0** to **SD3/SC3**. These are the multiplexed pins. Each one is a completely separate I2C bus set. You can have 4 I2C devices with identical addresses, as long as they are on one I2C bus each. The power input for the connectors is the output from the **Vout** pin, and is either **V+** or **3.3V 500mA**.
Warning:
## Address Pins
On the back of the board are **three address jumpers** , labeled **A0** , **A1** , and **A2,** below the board description text on the silkscreen. These jumpers allow you to chain up to 8 of these boards on the same pair of I2C clock and data pins. To do so, you solder the jumpers "closed" by connecting the two pads.
The default I2C address is **0x70**. The other address options can be calculated by adding the **A**** 0/A1/A2 **to the base of** 0x70**.
**A0** sets the lowest bit with a value of **1** , **A1** sets the next bit with a value of **2** and **A2** sets the next bit with a value of **4.** The final address is **0x70 + A2 + A1 + A0** which would be **0x77**.
So for example if **A2** is soldered closed and **A0** is soldered closed, the address is **0x70 + 4 + 1 = 0x75**.
If only **A0** is soldered closed, the address is **0x70 + 1 = 0x71**
If only **A1** is soldered closed, the address is **0x70 + 2 = 0x72**
If only **A2** is soldered closed, the address is **0x70 + 4 = 0x74**
The table below shows all possible addresses, and whether the pin(s) should be high (closed) or low (open).
## Reset Pin
- **RST** - Reset pin for resetting the multiplexer chip. Pulled high by default, connect to ground to reset.
## Vout Jumpers
These jumpers select between supplying the 4 STEMMA QT ports with either the incoming voltage on **V+** (3-5 VDC) or the output from the 3V regulator at 3.3V 500mA (labeled **3V** ). For example, if you're using this with a 5V microcontroller like an Arduino 328-compatible, you can level shift all the QT ports to have 3V power and logic level by cutting/soldering these jumpers.
- **V+ jumper** (default) - This jumper is located on the back of the board, to the right of the address jumpers. It supplies the incoming voltage on **V+** (3-5 VDC) to the attached multiplexed devices. Cut the trace to this jumper to disconnect V+ from the multiplexed devices and set the output voltage to 3.3V 500mA.
- **3V jumper** - This jumper is located on the back of the board, to the right of the address jumpers. Solder this pad to the center **Vout** pad to set the output logic level to 3.3V 500mA from the onboard 3V regulator.
## Power LED
- **Power LED -** In the upper left corner, above the STEMMA connector, on the front of the board, is the power LED, labeled **on**. It is the green LED.
# Adafruit PCA9546 4-Channel STEMMA QT Multiplexer
## CircuitPython & Python
It's easy to use the **PCA9546** with Python or CircuitPython, and the [Adafruit\_CircuitPython\_TCA9548A](https://github.com/adafruit/Adafruit_CircuitPython_TCA9548A) module. This module allows you to easily write Python code that allows you to multiplex up to 4 STEMMA boards with the **PCA9546** I2C multiplexer. You can use this multiplexer with any CircuitPython microcontroller board or with a computer that has GPIO and Python [thanks to Adafruit\_Blinka, our CircuitPython-for-Python compatibility library](https://learn.adafruit.com/circuitpython-on-raspberrypi-linux).
If you're curious why you'd need an I2C multiplexer, be sure to [check out this guide](https://learn.adafruit.com/working-with-multiple-i2c-devices) that goes in depth on working with _ **multiple** _ copies of the same I2C device, which most likely have the **same I2C address**.
[Working with Multiple Same Address I2C Devices Learn Guide](https://learn.adafruit.com/working-with-multiple-i2c-devices)
## Why the Adafruit\_CircuitPython\_TCA9548A Module?
The PCA9546 is the four output version of the PCA9548 and the PCA9548 is the 'fraternal twin sister' of the TCA9548. The PCA954x chips are easier to get during the great chip shortage of 2022-23. They work exactly the same, they just can't go down to 1.8V power which is OK because QT boards are 3V or 5V only anyways. [You can still use any example code or library for the TCA9546](https://learn.adafruit.com/adafruit-tca9548a-1-to-8-i2c-multiplexer-breakout/overview), but a **_PCA9546A class_** has been added to the library that only allows for reading up to four attached devices.
## CircuitPython Microcontroller Wiring
First, wire up a PCA9546 to your board exactly as shown below. Here's an example of wiring a Feather RP2040 to the PCA9546 with I2C using one of the handy [**STEMMA QT**](https://learn.adafruit.com/introducing-adafruit-stemma-qt) connectors. Then, plug two TSL2591 STEMMA boards into the PCA9548 via STEMMA plug 0 and STEMMA plug 1:
- **Feather 3V** to **multiplexer VIN (red wire)**
- **Feather GND** to **multiplexer**** GND (black wire)**
- **Feather SCL** to **multiplexer**** SCL (yellow wire)**
- **Feather SDA** to **multiplexer**** SDA (blue wire)**
- **TSL2591 1** to **multiplexer STEMMA port 0**
- **TSL2591 2** to **multiplexer STEMMA port 1**
## Python Computer Wiring
Since there's _dozens_ of Linux computers/boards you can use, below shows wiring for Raspberry Pi. For other platforms, [please visit the guide for CircuitPython on Linux to see whether your platform is supported](https://learn.adafruit.com/circuitpython-on-raspberrypi-linux).
Here's the Raspberry Pi wired to the I2C multiplexer using I2C and a [**STEMMA QT**](https://learn.adafruit.com/introducing-adafruit-stemma-qt) connector:
- **Pi 3V** to **multiplexer**** VIN (red wire)**
- **Pi GND** to **multiplexer**** GND (black wire)**
- **Pi SCL** to **multiplexer**** SCL (yellow wire)**
- **Pi SDA** to **multiplexer**** SDA (blue wire)**
- **TSL2591 1** to **multiplexer STEMMA port 0**
- **TSL2591 2** to **multiplexer STEMMA port 1**
## Python Installation of TCA9548A Library
You'll need to install the **Adafruit\_Blinka** library that provides the CircuitPython support in Python. This may also require enabling I2C on your platform and verifying you are running Python 3. [Since each platform is a little different, and Linux changes often, please visit the CircuitPython on Linux guide to get your computer ready](https://learn.adafruit.com/circuitpython-on-raspberrypi-linux)!
Once that's done, from your command line run the following command:
- `sudo pip3 install adafruit-circuitpython-tca9548a`
If your default Python is version 3, you may need to run `pip` instead. Make sure you aren't trying to use CircuitPython on Python 2.x, it isn't supported!
## CircuitPython Usage
To use with CircuitPython, you need to first install the TCA9548A library, and its dependencies, into the **lib** folder on your **CIRCUITPY** drive. Then you need to update **code.py** with the example script.
Thankfully, we can do this in one go. In the example below, click the **Download Project Bundle** button below to download the necessary libraries and the **code.py** file in a zip file. Extract the contents of the zip file, and copy the **entire **** lib ** ** folder ** and the ** code.py ** file to your ** CIRCUITPY** drive.
Your **CIRCUITPY/lib** folder should contain the following folders and file:
- **adafruit\_bus\_device/**
- **adafruit\_tca9548a.mpy**
- **adafruit\_tsl2591.mpy**
## Python Usage
Once you have the library `pip3` installed on your computer, copy or download the following example to your computer, and run the following, replacing **code.py** with whatever you named the file:
`python3 code.py`
## Simple Test Example Code
https://github.com/adafruit/Adafruit_CircuitPython_TCA9548A/blob/main/examples/pca9546a_simpletest.py
**If running CircuitPython:** Once everything is saved to the **CIRCUITPY** drive, [connect to the serial console](https://learn.adafruit.com/welcome-to-circuitpython/kattni-connecting-to-the-serial-console) to see the data printed out!
**If running Python: ** The console output will appear wherever you are running Python.
In this simple test for the PCA9546, an I2C scan is performed for all four of its ports. If any devices are connected, then the I2C address will be printed to the REPL next to the channel number. If no device is connected, then the port will print with empty brackets (`[]`).
## Multi-Sensor Example Code
https://github.com/adafruit/Adafruit_CircuitPython_TCA9548A/blob/main/examples/pca9546a_multisensor.py
In the multi-sensor example, the PCA9546 is used as an I2C multiplexer with two TSL2591 light sensors. When the connected sensors are instantiated over I2C, the I2C pins declared are the ports from `0` and `1` on the PCA9546.
In the example, the first TSL2591 light sensor, instantiated as `tsl1`, is plugged into STEMMA QT port 0 (`tca[0]`) and the second TSL2591 light sensor, instantiated as `tsl2`, is plugged into STEMMA QT port 1 (`tca[1]`).
```python
# Create the PCA9546A object and give it the I2C bus
mux = adafruit_tca9548a.PCA9546A(i2c)
# For each sensor, create it using the PCA9546A channel instead of the I2C object
tsl1 = adafruit_tsl2591.TSL2591(mux[0])
tsl2 = adafruit_tsl2591.TSL2591(mux[1])
```
In the loop, the readings from the two light sensors are printed to the REPL every `0.1` seconds.
```python
while True:
print(tsl1.lux, tsl2.lux)
time.sleep(0.1)
```
# Adafruit PCA9546 4-Channel STEMMA QT Multiplexer
## Python Docs
# Adafruit PCA9546 4-Channel STEMMA QT Multiplexer
## Arduino
Using the PCA9546 I2C multiplexer with Arduino involves wiring up the I2C multiplexer to your Arduino-compatible microcontroller and running the provided example code.
If you're curious why you'd need an I2C multiplexer, be sure to [check out this guide](https://learn.adafruit.com/working-with-multiple-i2c-devices) that goes in depth on working with _ **multiple** _ copies of the same I2C device, which most likely have the **same I2C address**.
[Working with Multiple Same Address I2C Devices Learn Guide](https://learn.adafruit.com/working-with-multiple-i2c-devices)
## Wiring
Wire as shown for a **5V** board like an Uno. If you are using a ** 3V** board, like an Adafruit Feather, wire the board's 3V pin to the PCA9546 VIN.
Here is an Adafruit Metro wired up to the PCA9546 using the STEMMA QT connector, along with two VL53L4CD STEMMA boards plugged into port 0 and port 1 on the PCA9546:
- **Metro 5V** to **multiplexer**** VIN (red wire)**
- **Metro GND** to **multiplexer**** GND (black wire)**
- **Metro SCL** to **multiplexer**** SCL (yellow wire)**
- **Metro SDA** to **multiplexer**** SDA (blue wire)**
- **VL53L4CD 1** to **multiplexer STEMMA port 0**
- **VL53L4CD 2** to **multiplexer STEMMA port 1**
## Library Installation
The Multi-Sensor example uses two VL53L4CD time of flight sensors. You can install the **VL53L4CD** library for Arduino using the Library Manager in the Arduino IDE.
Click the **Manage Libraries ...** menu item, search for **VL53L4CD** , and select the **STM32duino VL53L4CD** library:
## I2C Scanner Example Code
https://github.com/adafruit/Adafruit_Learning_System_Guides/blob/main/PCA9546_Demos/PCA9546_I2C_Scanner/PCA9546_I2C_Scanner.ino
Upload the sketch to your board and open up the Serial Monitor ( **Tools -\> Serial Monitor** ) at 115200 baud. You should see the 4 ports print to the Serial Monitor. If an I2C device is plugged into one of the ports, its address will be printed below the port number.
## Multi-Sensor Example Code
https://github.com/adafruit/Adafruit_Learning_System_Guides/blob/main/PCA9546_Demos/PCA9546_MultiSensors/PCA9546_MultiSensors.ino
Upload the sketch to your board and open up the Serial Monitor ( **Tools -\> Serial Monitor** ) at 115200 baud. You should see readings from the two VL53L4CD time of flight sensors print to the Serial Monitor.
# Adafruit PCA9546 4-Channel STEMMA QT Multiplexer
## Downloads
## Files
- [PCA9546 Datasheet](https://cdn-learn.adafruit.com/assets/assets/000/117/480/original/pca9546a.pdf?1673362983)
- [EagleCAD PCB files on GitHub](https://github.com/adafruit/Adafruit-PCA9546-PCB)
- [3D models on GitHub](https://github.com/adafruit/Adafruit_CAD_Parts/tree/main/5664%20PCA9546%20Stemma%20QT)
- [Fritzing object in the Adafruit Fritzing Library](https://github.com/adafruit/Fritzing-Library/blob/master/parts/Adafruit%20PCA9546%204-Channel%20STEMMA%20QT%20I2C%20Multiplexer.fzpz)
## Schematic and Fab Print
## Primary Products
### Adafruit PCA9546 4-Channel STEMMA QT / Qwiic I2C Multiplexer
[Adafruit PCA9546 4-Channel STEMMA QT / Qwiic I2C Multiplexer](https://www.adafruit.com/product/5664)
You just found the perfect I2C sensor, available in a handy chainable [**Qwiic, or STEMMA QT**](https://learn.adafruit.com/introducing-adafruit-stemma-qt) package, and you want to wire up two or three or four of them to your microcontroller when you realize...
In Stock
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[Related Guides to the Product](https://learn.adafruit.com/products/5664/guides)
## Featured Products
### 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.
Out of Stock
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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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[Related Guides to the Product](https://learn.adafruit.com/products/4399/guides)
### 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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### 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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### 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...
In Stock
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[Related Guides to the Product](https://learn.adafruit.com/products/4397/guides)
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