You can now create a dazzling display with your Raspberry Pi with the Adafruit RGB Matrix HAT or Bonnet. These boards plug into your Pi and makes it super easy to control RGB matrices such as those we stock in the shop and create a colorful scrolling display or mini LED wall with ease.

The RGB Matrix HAT works on any Raspberry Pi with a 40-pin GPIO header — Zero, Zero W/WH, Zero 2 W, Model A+, B+, Pi 2, 3, and 4. It does not work with older 26-pin boards like the original Model A or B, nor does it work with the Pi 400. Note with the Pi Zero you may need to solder a header on the Pi board; it’s normally unpopulated on that model (except the “Zero WH”).

This HAT is our finest to date, full of some really great circuitry. Let me break it down for you:

• Simple design - plug in power, plug in IDC cable, run our Python code!
• Power protection circuitry - you can plug a 5V 4A wall adapter into the HAT and it will automatically protect against negative, over or under-voltages! Yay for no accidental destruction of your setup.
• Onboard level shifters to convert the RasPi's 3.3V to 5.0V logic for clean and glitch free matrix driving
• DS1307 Real Time Clock can keep track of time for the Pi even when it is rebooted or powered down, to make for really nice time displays

Works with any of our 16x32, 32x32 or 32x64 RGB LED Matrices with HUB75 connections. The latest “Rev C” HAT also supports 64x64 matrices by soldering a small jumper on the PCB. You can even chain multiple matrices together for a longer display - we've only tested up to 32x128 but it works just fine. The bigger the display the harder it is on the Pi, so keep that in mind if you're using a lower-powered Pi Zero.

Please note: this HAT is only for use with HUB75 type RGB Matrices. Not for use with NeoPixel, DotStar, or other 'addressable' LEDs.

Each order comes with a HAT PCB with all surface mount parts assembled, a 2x20 female socket connector, a 2 pin terminal block, and a 2x8 IDC socket connector. A CR1220 coin cell is not included to make air shipping easier, please order one seperately if you do not have one and would like to use the real time clock.

RGB Matrix is not included, please check out our fine selection!

A 5V power supply is also required, not included, for power the matrix itself, the Pi cannot do it, to calculate the power, multiply the width of all the chained matrices * 0.12 Amps : A 32 pixel wide matrix can end up drawing 32*0.12 = 3.85A so pick up a 5V 4A power supply.

Raspberry Pi not included (but we have 'em in the shop so pick one up)

Some light soldering is required to attach the headers to your Pi. A soldering iron and solder are required, but it’s a simple soldering job and most beginners can do it in about 15 minutes.

This HAT uses a lot of pins to drive the RGB Matrix. You'll still have a couple left over but just be aware a majority are in use by the matrix.

Unused GPIO pins include: RX, TX, 25, MOSI, MISO, SCLK, CE0, CE1, 19.

Pin 24 is free if you are not using a 1/32 scan (i.e. 64x64) matrix.

Pin 18 is free if using the “convenience” (vs “quality”) setting during installation.

The 1-Wire interface as enabled by raspi-config will interfere with the operation of the matrix! By default it uses pin 4. If you are connecting any 1-Wire devices, specify a different pin (any of the above) in /boot/config.txt, for example:

dtoverlay=w1-gpio gpiopin=19

1

dtoverlay=w1-gpio gpiopin=19

I2C / RTC pins

The DS1307 Real Time Clock soldered onboard is connected to the I2C pins SDA and SCL - these can still be used for other I2C sensors and devices as long as they are not on address 0x68

To use the Real Time Clock, a CR1220 3V lithium battery is required.

5V protection circuitry and backpower diode

LED matrix panels require 5V power and a lot of it! 5V 2A at a minimum and you can easily need a 5V 4A or 5V 10A supply for big stretches of panels!

Because the lines are addressed, each matrix has 64 pixels (16x32 or 32x32 panels) or 128 pixels (for the 32x64 panels) lit at one time. Each pixel can draw up to 0.06 Amps each if on full white. The total max per panel is thus 64 * 0.06 = 3.95 Amps or 128 * 0.06 = 7.68 Amps

That's if all the LEDs are on at once, which is not likely - but still, its good to have at least half for the power supply in case you get bright!

5V power from a wall plug goes into the DC jack on the HAT which then goes through a fancy protection circuit that makes sure the voltage is not higher than 5.8V - this means that if you accidentally grab a 9V or 12V plug or a reverse polarity plug you will not damage the HAT, Pi and panels.  (Please note, this does not protect against extreme damage, if you plug in a 120VAC output into the DC jack or continuously try to plug in the wrong voltage you could still cause damage so please do be careful!)

We recommend powering your driving Raspberry Pi from the Pi's microUSB port but we do have a 1A diode on board that will automatically power the Pi if/when the voltage drops. So if you want, just plug in the 5V wall adapter into the HAT and it will automagically power up the Pi too!

The green LED next to the DC jack will indicate that the 5V power is good, make sure it is lit when trying to use the HAT!

Matrix Drive pins

The matrix does not work like 'smart' pixels you may have used, like NeoPixels or DotStars or LPD8806 or WS2801 or what have you. The matrix panels are very 'dumb' and have no memory or self-drawing capability.

Data must be constantly streamed to the matrix for an image to display! So all of these pins are always used when drawing to the display

All these pins go thru a 74AHCT145 level shifter to convert the 3.3V logic from the Pi to the 5V logic required by the panels

Matrix Color Pins

• Pi GPIO #5 - Matrix R1 (Red row 1) pin
  This pin controls the red LEDs on the top half of the display
• Pi GPIO #13 - Matrix G1 (Green row 1) pin
  This pin controls the green LEDs on the top half of the display
• Pi GPIO #6 - Matrix B1 (Blue row 1) pin
  This pin controls the blue LEDs on the top half of the display
• Pi GPIO #12 - Matrix R2 (Red row 2) pin
  This pin controls the red LEDs on the bottom half of the display
• Pi GPIO #16 - Matrix G2 (Green row2) pin
  This pin controls the green LEDs on the bottom half of the display
• Pi GPIO #23 - Matrix B2 (Blue row 2) pin
  This pin controls the blue LEDs on the bottom half of the display

Matrix Control pins

• Pi GPIO #4 - Matrix OE (output enable) pin
  This pin controls whether the LEDs are lit at all
• Pi GPIO #17 - Matrix CLK (clock) pin
  This pin is the high speed clock pin for clocking RGB data to the matrix
• Pi GPIO #21 - Matrix LAT (latch) pin
  This pin is the data latching pin for clocking RGB data to the matrix

RGB Matrix Address pins

• Pi GPIO #22 - Matrix A (address A) pin
  This pin is part of the 1->16 or 1->8 multiplexing circuitry.
• Pi GPIO #26 - Matrix B (address B) pin
  This pin is part of the 1->16 or 1->8 multiplexing circuitry.
• Pi GPIO #27 - Matrix C (address C) pin
  This pin is part of the 1->16 or 1->8 multiplexing circuitry.
• Pi GPIO #20 - Matrix D (address D) pin
  This pin is part of the 1->32, 1->16 multiplexing circuitry. Used for 32-pixel and 64-pixel tall displays only
• Pi GPIO #24 - Matrix E (address E) pin
  This pin is part of the 1->32 multiplexing circuitry. Used for 64-pixel tall displays only. Present on newer “Rev C” HATs only. Requires minor soldering, explained on next page.

Solder on Headers and Terminal Block

Before we can a-blinkin' there's a little soldering to be done. This step will attach the 2x20 socket header so that we can plug this HAT into a Raspberry Pi, the 2x8 header so we can plug the RGB matrix into the HAT, and a terminal block so you can power the matrix through the HAT.

64x64 Matrices: Solder “E” Jumper

64x64 matrices are supported on the latest “Rev C” HATs only.

Configure for 64x64 Matrix

Additional soldering is needed if using a 64x64 RGB Matrix.

Configure for Quality/Convenience

This an option picked when running the script to install the software. No additional work is needed if the "convenience" option is chosen. For the "quality" option, a connection is needed between GPIO4 and GPIO18. 

Additionally, normal audio output needs to be disabled if "quality" is chosen. Specifically, it is the snd_bcm2835 kernel module that needs to be disabled. The installer script will take care of that if the "quality" option is chosen. USB audio adapters should still work. But audio over HDMI or from the 1/8" audio jack will not be present. 

Step 1. Plug HAT/Bonnet into Raspberry Pi

Step 2. Connect Matrix Power cable to terminal block

Your RGB matrix came with a red & black power cable. One end has a 4-pin MOLEX connector that goes into the matrix. The other end probably has a spade connector. If you didn't get a spade connector, you may have to cut off the connector and tin the wires to plug them into the terminal block

Step 3. Connect RGB Matrix Data cable to IDC

Step 4. Power up your Pi via MicroUSB (optional but suggested)

Connect your Raspberry Pi to power via the microUSB cable, just like you normally would to power it up.

You can power the Pi via the 5V wall plug that is also used for the Matrix but its best to have it powered seperately

Step 5. Plug in the 5V DC power for the Matrix

Check that the Matrix plugs are installed and in the right location

Step 6. Log into your Pi to install and run software

OK now you are ready to install the RGB matrix driver software. You will need to get into a command line via the HDMI monitor, ssh or console cable. You will also need to make sure your Pi is on the Internet via a WiFi or Ethernet connection.

For using Raspberry Pi 5s with Python, see the following guide for software setup:

Continue with this guide to install software. There is an automated script that can be run. For people more comfortable with cloning repos and running make files, a manual install process is also shown. Pick whichever one seems best suited for your setup.

Setup Virtual Environment

If you are installing on the Bookworm version of Raspberry Pi OS or later, you will need to install your python modules in a virtual environment. You can find more information in the Python Virtual Environment Usage on Raspberry Pi guide. To Install and activate the virtual environment, use the following commands:

sudo apt install python3-venv
python -m venv env --system-site-packages

sudo apt install python3-venv
python -m venv env --system-site-packages

To activate the virtual environment:

source env/bin/activate

source env/bin/activate

Installer

You will need to get into a command line via the HDMI monitor, ssh or console cable. You will also need to make sure your Pi is on the Internet via a WiFi or Ethernet connection.

From the command line, use the following commands to run the installer script:

sudo apt install -y wget
pip3 install adafruit-python-shell
wget https://github.com/adafruit/Raspberry-Pi-Installer-Scripts/raw/main/rgb-matrix.py
sudo -E env PATH=$PATH python3 rgb-matrix.py

sudo apt install -y wget
pip3 install adafruit-python-shell
wget https://github.com/adafruit/Raspberry-Pi-Installer-Scripts/raw/main/rgb-matrix.py
sudo -E env PATH=$PATH python3 rgb-matrix.py

The LED-matrix library is (c) Henner Zeller [email protected] with GNU General Public License Version 2.0 http://www.gnu.org/licenses/gpl-2.0.txt

Earlier versions of this guide used our own fork of this library. That’s deprecated now, but still available if you have existing code built atop it. Otherwise, use this installer script and latest code.

When first run, the script will explain its plans and give you the option to cancel.

Of particular note here: any existing installation will be replaced. If there is a directory called “rpi-rgb-led-matrix” in the current working directory, its contents will be overwritten. If this is a problem, cancel and make a backup. Otherwise, sometimes reinstalling is exactly what you want.

Next the script will ask you what kind of adapter you’re using between the Pi and RGB matrix: either an Adafruit RGB Matrix Bonnet, or RGB Matrix HAT with RTC. If you select the latter, you’ll also be asked if you want to install additional drivers for the realtime clock. If you are using the Adafruit Triple LED Matrix Bonnet then select Adafruit RGB Matrix Bonnet.

Then you’re asked whether you need the absolute best image possible from the LED matrix, or can accept slightly reduced quality for the sake of simplicity.

The "quality" setting requires soldering the GPIO4 and GPIO18 pins together. See previous section for details. If you are using the Adafruit Triple LED Matrix Bonnet you should select "quality". The Adafruit Triple LED Matrix Bonnet does not require any additional soldering. The single matrix bonnet and HAT require additional soldering for the quality choice.

The “convenience” setting requires no changes and sound still works. For many casual projects this might look good enough. There’s an occasional bit of flicker from the matrix, that’s all.

If you're using a single matrix bonnet or HAT, and you’re not sure, or if you just want to get started experimenting with your new gadget, select “convenience” for now. You can make the change and reinstall the software later if needed.

The script will confirm your selections and offer one more chance to cancel without changes.

There’s a lot of software to update, download and install, so it may take up to 15 minutes or so to complete. Afterward, you’ll be asked whether you want to reboot the system. If you’ve selected to install RTC support (for the Matrix HAT + RTC) or have made a change in the “quality” vs “convenience” setting, a reboot is required.

All other settings (LED matrix size, number of “chained” matrices and so forth) are specified at run-time.

Once the Pi has rebooted, log back in and continue to the Testing Install section.

Install Prerequisites

Make sure these are installed:

sudo apt-get install -y git python3-dev python3-pillow cython3 python3-setuptools

sudo apt-get install -y git python3-dev python3-pillow cython3 python3-setuptools

Source Code

The code used to drive the matrices is found in this repo:

There is good information found there in various README's and that might be all you need. The information that follows serves more as a general example of how to get the code and build the main targets.

Clone and Build

The project is makefile based, so it is fairly easy to clone the repo and build the target(s):

git clone https://github.com/hzeller/rpi-rgb-led-matrix.git
cd rpi-rgb-led-matrix
make

git clone https://github.com/hzeller/rpi-rgb-led-matrix.git
cd rpi-rgb-led-matrix
make

The default target builds the library as well as the C examples found in the examples-api-use subdirectory. It should be possible to run those examples after the build completes:

cd examples-api-use
sudo ./demo -D 0

cd examples-api-use
sudo ./demo -D 0

Dealing with "quality" vs. "convenience"

The default build uses a hardware subsystem on the Pi that is also used for audio on HDMI and the 1/8" jack. This is the "quality" option referred to by the installer script and it also requires connecting GPIO 4 to 18 on the HAT/Bonnet. So there is a hardware resource conflict that must be resolved. The demo programs will report this with the following message:

=== snd_bcm2835: found that the Pi sound module is loaded. ===
Don't use the built-in sound of the Pi together with this lib; it is known to be
incompatible and cause trouble and hangs (you can still use external USB sound adapters).

See Troubleshooting section in README how to disable the sound module.
You can also run with --led-no-hardware-pulse to avoid the incompatibility,
but you will have more flicker.
Exiting; fix the above first or use --led-no-hardware-pulse

=== snd_bcm2835: found that the Pi sound module is loaded. ===
Don't use the built-in sound of the Pi together with this lib; it is known to be
incompatible and cause trouble and hangs (you can still use external USB sound adapters).

See Troubleshooting section in README how to disable the sound module.
You can also run with --led-no-hardware-pulse to avoid the incompatibility,
but you will have more flicker.
Exiting; fix the above first or use --led-no-hardware-pulse

The other option is to disable the hardware pulsing feature of the RGB matrix driver software. This is the "convenience" option referred to by the installer script.

More info on these two options:

Option 1: Disable Sound for Hardware Pulsing ("quality")

To disable the Pi audio, blacklist it. Create a file named /etc/modprobe.d/blacklist-rgb-matrix.conf with the contents:

blacklist snd_bcm2835

blacklist snd_bcm2835

and then reboot the Pi.

Option 2: Disable Hardware Pulsing ("convenience")

The command line parameter --led-no-hardware-pulse can be used to turn off this feature in the RGB matrix driver software at run time:

sudo ./demo --led-no-hardware-pulse -D 0

sudo ./demo --led-no-hardware-pulse -D 0

It can also be disabled at build time using the DISABLE_HARDWARE_PULSES preprocessor directive: 

make USER_DEFINES="-DDISABLE_HARDWARE_PULSES"

make USER_DEFINES="-DDISABLE_HARDWARE_PULSES"

Python Build

There are two targets for this: build-python and install-python. The install target uses an older (setup.py) approach. However, it seems to generally work OK to create and activate a Python virtual environment and then use the install-python target:

python3 -m venv test
source test/bin/activate
cd rpi-rgb-led-matrix
make install-python

1
2
3
4

python3 -m venv test
source test/bin/activate
cd rpi-rgb-led-matrix
make install-python

It also works to use the build-python target and then manually run setup.py with a virtual environment active. The build-python and install-python targets are dependent on the main library target, so if the goal is to have Python bindings, either of those can be used as the build target, i.e. just build everything in one make execution.

The installer creates a directory called rpi-rgb-led-matrix, and inside this is a subdirectory examples-api-use with a few programs we can use to experiment with the matrix and confirm everything’s working.

To run these examples, first change to the directory:

cd ~/rpi-rgb-led-matrix/examples-api-use/

cd ~/rpi-rgb-led-matrix/examples-api-use/

We'll use the demo program to test the setup. Here is an example for a 32x32 LED matrix. Note the program must be run with sudo.

sudo ./demo --led-rows=32 --led-cols=32 --led-gpio-mapping=adafruit-hat -D 0

sudo ./demo --led-rows=32 --led-cols=32 --led-gpio-mapping=adafruit-hat -D 0

Change the following parameters as needed for your setup:

• --led-row= set this to the number of LEDs in each matrix row
• --led-cols= set this to the number of LEDs in each matrix column
• --led-gpio-mapping= set this to adafruit-hat or adafruit-hat-pwm for single matrix bonnet/HAT. For triple matrix bonnet use regular
• --led-parallel= set this to 3 if you are using the triple matrix bonnet or other active3 compatible hardware. Otherwise it can be omitted.

Running the demo program:

should result in a rotating square on the matrix:

The -D parameter picks the specific demo to run. There are several to choose from, some with additional parameters:

Demos, choosen with -D
	0  - some rotating square
	1  - forward scrolling an image (-m <scroll-ms>)
	2  - backward scrolling an image (-m <scroll-ms>)
	3  - test image: a square
	4  - Pulsing color
	5  - Grayscale Block
	6  - Abelian sandpile model (-m <time-step-ms>)
	7  - Conway's game of life (-m <time-step-ms>)
	8  - Langton's ant (-m <time-step-ms>)
	9  - Volume bars (-m <time-step-ms>)
	10 - Evolution of color (-m <time-step-ms>)
	11 - Brightness pulse generator

Demos, choosen with -D
	0  - some rotating square
	1  - forward scrolling an image (-m <scroll-ms>)
	2  - backward scrolling an image (-m <scroll-ms>)
	3  - test image: a square
	4  - Pulsing color
	5  - Grayscale Block
	6  - Abelian sandpile model (-m <time-step-ms>)
	7  - Conway's game of life (-m <time-step-ms>)
	8  - Langton's ant (-m <time-step-ms>)
	9  - Volume bars (-m <time-step-ms>)
	10 - Evolution of color (-m <time-step-ms>)
	11 - Brightness pulse generator

Tuning the Demo

Depending on your matrix type and Raspberry Pi model, some additional options may need fine-tuning:

--led-slowdown-gpio=(0…n) Sometimes needed to throttle back the speed when using a fast Pi. Default is 1.

For Raspberry Pi 3 use a slowdown of 1 to start (use higher values if image still flickers). For Raspberry Pi 4, use a slowdown of 4. Older Pi models might work with 0, try it.

--led-rgb-sequence=(RGB order) Some LED matrices may have their red, green and blue LEDs wired up in a different order…for example, if you need to swap the green and blue channels, use --led-rgb-sequence=RBG. Default is RGB.

--led-pwm-bits=(1…11) For long matrix chains you’ll probably need to use fewer PWM bits, sacrificing some color fidelity to improve refresh speed. Default is 11.

The installer script builds the Python bindings, but does not install them. We want to install things into a Python virtual environment. So the first step is to create the venv and activate it. We'll call the venv rgbmatrix and locate it in the pi user's home folder:

cd
python3 -m venv rgbmatrix
source rgbmatrix/bin/activate

cd
python3 -m venv rgbmatrix
source rgbmatrix/bin/activate

Next, cd back into the directory the repo was cloned into and run make with the install-python target:

cd rpi-rgb-led-matrix/
make install-python

cd rpi-rgb-led-matrix/
make install-python

That should install the Python support into the venv.

There are some Python examples found in the bindings/python/samples subfolder that can be used to test the setup. The examples must be run with sudo, which can be tricky when used within a venv. The Python virtual environment guide has more information on how to deal with this. 

Here is an example:

cd bindings/python/samples/
sudo -E env PATH=$PATH python3 simple-square.py --led-rows=32 --led-cols=32 --led-gpio-mapping=adafruit-hat

cd bindings/python/samples/
sudo -E env PATH=$PATH python3 simple-square.py --led-rows=32 --led-cols=32 --led-gpio-mapping=adafruit-hat

That should result in output on the RGB matrix that looks like this:

Parameters can be set via the command line. Change the following parameters as needed for your setup:

• --led-row= set this to the number of LEDs in each matrix row (default=32)
• --led-cols= set this to the number of LEDs in each matrix column (default=32)
• --led-gpio-mapping= set this to adafruit-hat or adafruit-hat-pwm (default=regular)

Another Basic Example

The examples in the library repo have a sort of object-orientated design which may make things look overly complicated. Additionally, there is a lot of code dealing with parsing the command line options. All of the command line parameters can be configured directly in code.

Here is another example to show more simply how the RGB matrix can be used in Python:

import time
from random import randrange
from rgbmatrix import RGBMatrix, RGBMatrixOptions

options = RGBMatrixOptions()

options.hardware_mapping = 'adafruit-hat'
options.rows = 32
options.cols = 32

matrix = RGBMatrix(options = options)

while True:
    matrix.Clear()
    for _ in range(1000):
        r = randrange(256)
        g = randrange(256)
        b = randrange(256)
        x = randrange(32)
        y = randrange(32)
    
        matrix.SetPixel(x, y, r, g, b)

        time.sleep(0.01)

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

import time
from random import randrange
from rgbmatrix import RGBMatrix, RGBMatrixOptions

options = RGBMatrixOptions()

options.hardware_mapping = 'adafruit-hat'
options.rows = 32
options.cols = 32

matrix = RGBMatrix(options = options)

while True:
    matrix.Clear()
    for _ in range(1000):
        r = randrange(256)
        g = randrange(256)
        b = randrange(256)
        x = randrange(32)
        y = randrange(32)
    
        matrix.SetPixel(x, y, r, g, b)

        time.sleep(0.01)

The general idea is to create an instance of the RGBMatrixOptions class and then set things as desired. Then create an instance of the RGBMatrix class and pass in the options.

The only documentation other than the examples is the source code itself, as linked from the repo readme. Here is a terse summary of the available functions and properties.

The RGBMatrixOptions class has the following properties:

brightness
chain_length
cols
daemon
disable_hardware_pulsing
drop_priv_group
drop_priv_user
drop_privileges
gpio_slowdown
hardware_mapping
inverse_colors
led_rgb_sequence
limit_refresh_rate_hz
multiplexing
panel_type
parallel
pixel_mapper_config
pwm_bits
pwm_dither_bits
pwm_lsb_nanoseconds
row_address_type
rows
scan_mode
show_refresh_rate

brightness
chain_length
cols
daemon
disable_hardware_pulsing
drop_priv_group
drop_priv_user
drop_privileges
gpio_slowdown
hardware_mapping
inverse_colors
led_rgb_sequence
limit_refresh_rate_hz
multiplexing
panel_type
parallel
pixel_mapper_config
pwm_bits
pwm_dither_bits
pwm_lsb_nanoseconds
row_address_type
rows
scan_mode
show_refresh_rate

The RGBMatrix class has the following functions and properties:

Clear()
CreateFrameCanvas()
Fill()
SetImage()
SetPixel()
SetPixelsPillow()
SwapOnVSync()
brightness
height
luminanceCorrect
pwmBits
width

Clear()
CreateFrameCanvas()
Fill()
SetImage()
SetPixel()
SetPixelsPillow()
SwapOnVSync()
brightness
height
luminanceCorrect
pwmBits
width

We had a little space and thought a real time clock would be a nice pairing for this HAT so we tossed on a DS1307 real time clock (RTC). This clock uses a 32.768KHz crystal and backup battery to let the HAT & Pi keep track of time even when power is lost and there's no network access. This makes it great for time displays!

A 12mm 3V Lithium Coin Cell (CR1220) is REQUIRED to use the RTC! It will not work without one!

The rgb-matrix.sh script already installed the necessary software to use the realtime clock…but you’ll need to set the initial time once. This is explained in the “Sync time from Pi to RTC” section of this DS1307 tutorial (just that one section…you can ignore the rest).

Datasheets

• DS1307 Real Time Clock
• MAX4866 5V protection chip
• Fritzing object in the Adafruit Fritzing Library
• EagleCAD PCB files on GitHub

Schematic

Click to embiggen

Fabrication Print

Here's the fabrication print with dimensions in inches. This HAT is compatible with the Raspberry Pi mechanical HAT specification!