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The Raspberry Pi is a series of minicomputers that have become popular with many users around the world at a dizzying pace. They are a very good tool for many everyday tasks, such as programming applications for embedded systems, browsing the Internet, playing multimedia content, and they also work perfectly as drivers for various hardware applications. Using the on-board GPIO port bus, most Raspberry Pi models can work with dedicated HATs. The article describes the features of HAT add-on modules for the Raspberry Pi, which are worth choosing especially at the beginning of the adventure with this hardware and software platform, and which offer many practical applications in projects with different levels of expansion.
Raspberry Pi PoE HAT
The powering of the Raspberry Pi using the Internet was one of the most anticipated features among the users. The ability to access the Internet through a single cable and power the Raspberry at the same time can prove to be a very practical advantage, especially when the computer is not stationary. Moreover, in Pi 3B + and 4B models, the board has four additional pins in the GPIO area, thanks to which you can take advantage of all the possibilities offered by the PoE. In its design, the PoE shield uses a small, specially designed isolation transformer that converts the Ethernet-level voltage, i.e. from 37VDC to 57VDC to 5VDC, which is safe for the Raspberry Pi. Since the isolation transformer does not take up much space, the designers have also equipped this module with a fan. This makes the PoE HAT a perfect complement to the Raspberry Pi and allows it to be used in industrial applications. The problem of a separate power supply for the Raspberry Pi is eliminated and its reliability and efficiency are increased. This is achieved by the use of a fan-operated circulating air cooling.
ModMyPi Jam HAT
Many of the projects that are most popular with beginning users of the Raspberry Pi use LEDs, buttons and buzzers. The ModMyPi Jam HAT includes all of these elements on a small board compatible with the Raspberry Pi. There are six LEDs (red, orange and green – two for each color), two monostable pushbuttons, and a piezoelectric generator (buzzer). The Jam HAT board is an excellent solution for anyone taking their first steps in the hardware and software operation of the Raspberry Pi and allows you to learn the principles of operating the pushbuttons as basic input elements and the LED and buzzer as basic output elements. Based on this board we can build e.g. a traffic light emulator controlled by buttons.
Pimoroni Breakout Garden HAT
Pimoroni’s Breakout Garden HAT is a great way to develop projects without having to solder and connect extra, unnecessary cables. Unlike modular systems that use wires and connectors to communicate with each other, with the Pimoroni Breakout Garden HAT board, all you need to do is connect small dedicated modules that work together, placed on circuit boards, to small pins and you can start using them right away. Among these modules are thermal imaging camera, small display or measurement sensors. The board has built-in reverse polarity protection. Regardless of which slot you use on the board, the software automatically detects the type of module connected to the socket via the I2C bus, even if they are connected in the opposite way. The set includes a 1×20 strip of male header that can be soldered to the GPIO ports of the board.
HiFiBerry DAC+ ADC
There are many audio-type HATs available on the market that have an integrated digital-to-analog converter and also include the HiFiBerry shields. It has a small, but at the same time big difference when compared with other audio shields – it also has an analog-to-digital converter, thanks to which it also allows input and processing of the input signal, allowing you to record or process the input audio signal. This shield is very well suited for home music production and podcast recording. The hardware configuration of the DAC + ADC shield is very simple, but requires the installation of the Linux 4.18.12 kernel to use the on-board ADC. Complete documentation with installation instructions is available on the manufacturer’s website. The Burr-Brown PCM5122 DAC has an excellent track record in other computer audio devices, providing very good quality audio file playback. The output signal from the converter is routed through the output amplifier and fed to the stereo output, which is equipped with RCA connectors. The on-board ADC is Burr-Brown PCM1861. The signal is fed to the analog 3.5mm TRS input, to which you can connect the audio signal of an MP3 player, telephone or other audio devices with line output. Thanks to this, the HiFiBerry overlay can be a useful tool for playing music at parties, recording your musical ideas, and as a platform for sound processing with the use of effects such as reverb or distortion.
Pimoroni Unicorn HAT HD
This shield allows you to create various animations, as well as display low-resolution movies and photos. The set includes a gold pin header factory-attached to the shield’s GPIO pins, so no soldering is required. The diffuser should be mounted to the LED matrix using the mounting elements included in the kit. The diffuser makes a huge difference to the final visual effect, as it selectively diffuses the light from the matrix so that you cannot see the lines separating the individual LEDs. The degree of light blur is regulated by adjusting the height of the diffuser relative to the LED matrix. The pad communicates with the Raspberry Pi via the SPI interface, for which four GPIO pins are responsible, including those responsible for the power supply. The shield uses its own ARM STM32F processor, which has high processing power necessary for the Raspberry Pi to work with a triple LED driver. As a result, there are no delays in data exchange between the shield and the Raspberry Pi. A low-resolution video file is loaded into the memory installed on the shield, showing a sample image captured with the camera module (connected to the CSI port of the Raspberry Pi) and sample demo animations with some visual effects. The Unicorn HAT HD overlay comes with a special Python library that contains functions that allow you to adjust the brightness of the matrix and its other parameters. There is also a program called Unicorn Paint, which allows you to upload your drawings to the shield using a web browser. Thanks to the use of an independent processor, it is possible to easily connect several copies of the Unicorn HAT HD to a single Raspberry Pi computer.
Pimoroni Piano HAT
The latest version of the shield, based on the Pi Piano design, uses the interface of capacitive touch buttons imitating a single octave of the piano keyboard, i.e. 13 keys – from C to C one octave higher. The shield measures 64mm x 56mm and is compatible with the highest models of Raspberry Pi computers from the Pi 2, Pi 3A +, Pi 3B + and Pi 4B series. As was the case with the HAT shields, there is a 40-pin GPIO connector on the board. On the front there are buttons next to the keyboard, with which we can control the frequency range of the keyboard sounds (“octave up” / “octave down”) and also change presets. The shield’s software – Piano HAT – was created in the Python environment and can use other existing projects of programs written for this shield. There’s a program in the shield’s memory that uses flashing LEDs to teach the user how to play simple melodies. This factory library also allows the user to write their own instructions for playing any song. The design of the overlay also supports the possibility of cooperation with musical instruments using the MIDI protocol.
4tronix RoboHAT
The RoboHAT from 4Tronix is a small, powerful robot controller and the big brother of the Picon Zero. The shield is adapted to work with all models of the Raspberry Pi minicomputer, which are equipped with a 40-pin header as standard. As with the Picon Zero, the RoboHAT is characterized by high functionality thanks to the large number of pins for inputs, outputs and control connectors for robots. All components are pre-soldered on a high-quality PCB, so we can quickly connect the shield to the Raspberry Pi right out of the box. In addition, among the connectors on the board are ARK connectors for connecting a power supply and two DC motors. The board also contains a number of pins required to connect the ultrasonic distance sensor, as well as another ten input/output ports for communication via the I2C interface. If we are not using the ARK connector to power the shield, we can also connect the power supply via the 2.5mm / 5.5mm DC connector. The required output voltage of the power supply is between 7V and 11V. The manufacturer provides a set of practical programs and scripts in Python and the corresponding instructions and examples to facilitate the programming of the shield. For example, using the dedicated robohat.forward () library, a robot equipped with the RoboHAT shield can move forward. The shield works perfectly with the Raspberry Pi and many modules and elements popular among robot builders, and allows rapid prototyping of many interesting projects. It is also an excellent proposal for those who want to start their adventure with robotics and learn its practical basics, combining business with pleasure.
Pimoroni Mote pHAT
With its 16 very bright RGB LEDs, the Mote pHAT shield makes an excellent miniature lighting fixture for a closet or as an additional, nighttime lighting fixture for a room. It will help you create truly unique atmosphere, as well as serve a source of special lighting effects. The shield has small dimensions and is compatible with the Raspberry Pi Zero. The kit comes with a female header that must be soldered to the board. Thanks to this solution, we get the possibility to connect several shields to a single Raspberry Pi base unit, creating a more extensive application project. The built-in controller allows the overlay to communicate independently with LED sticks via four USB ports. The manufacturer provides a dedicated library in the Python environment along with several sample programs for controlling LED sticks, such as the rainbow-like effect, color mixing, and the CheerLights application that lets you control LED sticks over the Internet. Dedicated libraries are easy to use and allow you to precisely adjust the light color of each channel. LED sticks and connection cables are sold separately.
Adafruit Mini Kit TB6612
With the Mini Kit, the shield from Adafruit, you can control up to four DC motors or up to two stepper motors by controlling their speed via PWM channels. The shield is compatible with the GPIO pins of the Raspberry Pi. The control system on the shield allows full control over the speed and direction of rotation of the rotors of the controlled motors. The control is done via the I2C interface. In total, we can connect up to 32 overlays in parallel mode via the GPIO ports, allowing simultaneous real-time control of up to 64 stepper motors or up to 128 “normal” DC motors. As control devices, the shield uses two TB6612 integrated circuits based on MOSFET transistors and fast flyback diodes, which show maximum continuous current efficiency of up to 1.2A per single channel and 3.0A for about 20ms. The board also features reverse polarity protection and a small area of solder pads for prototyping. The kit comes with connectors that you just need to solder to the shield.
Adafruit Capacitive Touch HAT
The Capacitive Touch shield from Adafruit allows you to build interesting interactive projects. The module has twelve inputs equipped with capacitive touch sensors. Cables with alligator clips can be used to connect various objects with good properties in terms of electrical conductivity to the shield, which can be used as a control signal source under the influence of human or animal touch, thus starting a process implemented in the program, such as turning on lights or ventilation, or – a bit more elaborate – a piano with a keyboard with fruits instead of keys! There’s an easy-to-use library that reads the inputs of the interface.
SparkFun RELAYplate
RELAYplate from SparkFun’s Pi-Plates series is the first relay module designed specifically for Raspberry Pi microcomputers. On the board there are seven electromechanical relays with the configuration of SPST-NO normally open contacts (a relay with a single-pole single-throw contact that has opened circuit state when no current is applied). Each relay can be supplied with 120V AC or 30V DC and can handle circuits with a maximum current consumption of 1A. The position of the contacts of each of the relays is indicated by on-board LEDs. A maximum of eight boards can be connected in one system, allowing 56 relays to be operated simultaneously. The overlay can also be cascaded with DAQCplate and MOTORplate to create a comprehensive control system. The GPIO bus has a pinout compatible with Raspberry Pi 2B +, Pi 3B + and Pi 4B minicomputers. The set also includes an insulating cover of the relays to protect against touching the elements of the shield that may be under voltage exceeding safe limits.
Summary
The Raspberry Pi extension shields described in this article were subjectively chosen by the author and represent only the tip of the iceberg among a multitude of available shields for various applications. Regardless of the purpose of our project and its level of expansion, we must make the right choice by looking first and foremost at the hardware requirements that the project must meet, such as the number of inputs/outputs needed to support peripheral systems. The HAT modules presented are versatile, and since the Raspberry Pi computer project is still evolving in terms of computing power, more shields are sure to come on the market in the future, allowing you to create applications for even more demanding tasks.
