A Bounty of HATs and Clones
While basically the most popular SBC among hobbyists, professional engineers are also seeing the value of Raspberry Pi’s growing ecosystem of products. Raspberry Pi HATs of all kinds have emerged, targeting everything from data acquisition to air quality measurement.
The popularity of the Raspberry Pi product line of open-spec SBCs is truly astounding. In surveys of LinuxGizmos’s readers, we’ve found that year after year Raspberry Pi SBCs are the most popular open-spec SBCs. (LinuxGizmos.com is Circuit Cellar’s sister website). Raspberry Pi’s targeted audience has traditionally been DIY builders, makers, electronics hobbyists and the like. But the open-spec nature of Raspberry Pi has led to huge interest among professional engineers for two reasons.
First, board vendors have been able to develop clones of Raspberry Pi SBCs, that either match their functionality or simply offer the same connector scheme. Second, the emergence of Raspberry Pi add-on boards, called HATs, has resulted in the development of a wide variety of add-on functions that professional engineers need for all kinds of applications. HAT stands for “hardware attached on top,” a hardware specification for add-on modules for the Raspberry Pi model B+ SBC. HATs have several advantages compared to older add-on modules for the Raspberry Pi, such as no soldering required. In other words, HATs can be plugged right onto the Raspberry Pi’s connector.
With all that in mind, the real story about Raspberry Pi can arguably said to revolve around HAT products, rather than the SBCs themselves. Every month, new HAT products have emerged targeting an impressively wide set of functions and application needs. In fact, such new products are so frequent, that you’ll notice that many of the products covered in this article were released as recently as July and August.
MACHINE CONDITIONING HAT
Exemplifying these trends, the latest Raspberry Pi offering from Measurement Computing is its MCC 172 IEPE Measurement HAT for Raspberry Pi released in May. Well suited for machine condition monitoring and edge computing applications, the MCC 172 is a two-channel, high-speed DAQ HAT for making sound and vibration measurements from IEPE sensors like accelerometers and microphones (Figure 1). It features two, simultaneous, 24 bit analog inputs, with sample rates up to 51.2KS/s per channel.
Up to eight MCC HATs can be stacked onto one Raspberry Pi. MCC offers a variety of DAQ HATs that enable users to configure multifunction, Pi-based solutions with analog input, output and digital I/O. The open-source MCC DAQ HAT Library of commands in C/C++ and Python allows users to develop applications on Linux. The library is available to download from GitHub. Comprehensive API and hardware documentation are also provided.
The MCC 172 header plugs into the 40-pin general purpose I/O (GPIO) connector on a user-supplied Raspberry Pi SBC. The MCC 172 was tested for use with all Raspberry Pi models with the 40-pin GPIO connector. Multiple MCC 172 HATs can be synchronized to a single sampling clock. The clock is programmable for sampling rates between 51.2KS/s to 200 samples/s.
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HAT configuration parameters are stored in an on-board EEPROM that allows the Raspberry Pi to automatically set up the GPIO pins when the HAT is connected. The MCC 172 is powered with 5V provided by the Raspberry Pi through the GPIO header connector. The trigger input (terminal TRIG) is used to delay an input scan until a specified condition is met at the trigger input.
AUDIO AMPLIFIER HAT
While Raspberry Pi is aimed at hobbyists and “makers,” the rich variety of HATs available has attracted professional embedded system developers that want to take advantage of what’s available. Some such HATs include products that are aimed at users and makers. In an example along those lines, in May Infineon Technologies released what it claims is the world’s first fully self-contained Raspberry Pi audio amplifier HAT board (Figure 2).
The board (KIT_40W_AMP_HAT_ZW) offers high definition audio at boom box power levels in a small form factor. The Infineon proprietary multilevel technology ensures minimum size and consumption, state of the art power efficiency and HD audio quality for Raspberry Pi users and makers. Infineon markets the product for systems such as active speakers with wireless music streaming.
The board is compatible with Raspberry Pi Zero W and Raspberry Pi 3 and 4 SBCs. It leverages the MERUS multilevel class D amplification enabled by the MERUS MA12070P amplifier, which allows for filter-free amplifier design that does not need to use a filter-coil at the output filter. This significantly reduces the BOM cost and enables PCB area reduction. The board furthermore scores high output power in small form factor up to 40W instantaneous peak power at 4Ω. The solution offers best-in-class efficiency and playback time up to 20 hours with a 6700mA-hour power bank. There is no need for additional power supplies, only a single 5V/2.5A USB power supply is required for both the Raspberry Pi and the HAT.
For a quick and easy audio system setup, the board is compatible with the main Linux distributions such as Raspbian, Volumio, moOde Audio or JustboomPlayer. Dual-channel bridge-tied load (BTL) or single-channel parallel bridge-tied load (PBTL) configurations for Multiroom, TWS, or subwoofer applications are also possible.
pHAT FOR GNSS
Once again illustrating the diverse ecosystem of Raspberry Pi add-on boards available, in July SparkFun launched ZED-F9R GPS pHAT, a high precision, sensor fusion GPS board with impressive configuration options. It embeds U-blox’s Automotive Dead Reckoning (ADR) technology. SparkFun says the ZED-F9R module provides a highly accurate and continuous position by fusing a 3D IMU sensor, wheel ticks, a vehicle dynamics model, correction data and GNSS measurements. Sparkfun follows its pHAT (for partial HAT) approach, which doesn’t support all the specs of the official Raspberry Pi HAT.
The ZED-F9R module is a 184-channel U-blox F9 engine GNSS receiver, meaning it can receive signals from the GPS, GLONASS, Galileo and BeiDou constellations with approximately 0.2-meter accuracy. Such accuracy can be achieved with an RTK navigation solution when used with a correction source. Note that the ZED-F9R can only operate as a rover, so you will need to connect to a base station. The module supports concurrent reception of four GNSS systems. The combination of GNSS and integrated 3D sensor measurements on the ZED-F9R provide accurate, real-time positioning rates of up to 30Hz.
Compared to other GPS modules, this pHAT maximizes position accuracy in dense cities or covered areas, says the company. Even under poor signal conditions, continuous positioning is provided in urban environments and is also available during complete signal loss (such as short tunnels and parking garages). The ZED-F9R is a solution for autonomous robotic applications that require accurate positioning under challenging conditions.
The U-blox receiver supports a few serial protocols. By default, SparkFun chose to use the Raspberry Pi’s serial UART to communicate with the module. With pre-soldered headers, no soldering is required to stack the pHAT on a Raspberry Pi, NVIDIA Jetson Nano, Google Coral or any SBC with the 2×20 pin connector header. The board breaks out a few 0.1″-spaced pins from the U-blox receiver. A Qwiic connector is also added in case you need to connect a Qwiic-enabled device.
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AIR QUALITY SENSOR HAT
Some Raspberry Pi HAT manufacturers have been keen to leverage the technologies of sensor vendors. In an example along those lines, in August, Avnet launched a Renesas-sensor-based Indoor Air Quality HAT for Raspberry Pi called the AES-RHSEN-ZM44-G (Figure 3). The HAT features an on-board calibrated Renesas ZMOD4410 sensor that measures the concentrations of total volatile organic compounds (TVOCs) from parts-per-billion to parts-per-million and measures estimate carbon dioxide (eCO2) levels. These are important indicators for monitoring indoor air quality. All sensors are electrically and chemically (gas) tested with lab calibration data stored in each ZMOD4410 sensor’s built-in nonvolatile memory.
In addition to the ZMOD4410 sensor, the HAT incorporates a Renesas HS3001 high-precision relative humidity and temperature sensor, along with software-controlled status LEDs. Connection points are also available to measure the ZMOD4410 active current consumption, which is useful when integrating the sensor and its software into products powered by extended life batteries.
Potential applications for the board range from air/health monitoring systems, smart home appliances, smart thermostats, smart speakers and smart fans to smoke alarms, vacuum cleaners, garage openers, security systems, HVAC controls, air purifiers and building automation. The ZMOD4410 indoor air quality platform is available in four software configurations providing various sensor behaviors targeting unique applications indoors.
Avnet provides a pre-compiled test application that runs on the Raspberry Pi operation system and can measure TVOC and eCO2 out of the box. The application is built with Renesas’ proprietary licensed algorithms. For production purposes, customers may obtain the algorithms directly from Renesas under terms of their software license agreement.
PANEL PC FOR RASPBERRY Pi
In July, Comfile introduced the ComfilePi CPi-A150WR, a Raspberry Pi-based industrial panel PC with a 15″ touch-panel display. Leveraging the compact Raspberry Pi3 SBC, the ComfilePi CPi-A150WR inherits the Raspberry Pi 3’s 1.2GHz 64 bit quad-core Arm Cortex-A53 processor, a Broadcom VideoCore IV GPU and 1GB of RAM (Figure 4). The new, larger version has the same capabilities as its predecessors with smaller screen sizes: the 7″ CPi-A070WR and the 10.2″ CPi-A102WR. All models in the series now support AdvancedHMI software, based on the .NET framework, which uses the popular Visual Studio design environment. AdvancedHMI enables the creation of HMIs that are not possible with other off-the-shelf packages. It creates a true, fast executable for the Linux-based ComfilePi.
The CPi-A150WR’s display is a 24-bit color LCD with a resistive touchscreen, and the controller itself provides 22x ESD-protected GPIO lines, 3x USB 2.0 host ports, 1x RJ-45 Ethernet port, 1x I2C port, 1x RS-485 port, a 1x RS-232C port and a battery-backed RTC. It also features stereo audio output as well as a piezo buzzer. Wi-Fi is also possible using an external USB dongle. This 15″ ComfilePi requires a 12-24VDC 21W power input. The CPi-A150WR is housed in a flame-retardant ABS enclosure with an IP65 water resistant front panel, and is specified for an operating temperature range of 0°C to 70°C.
While Raspberry Pi SBCs typically run the Linux operating system, the ComfilePi can be programmed in almost any language, including C, C++, Java, JavaFX, Javascript, python, C#, vb.net and even emerging languages such as Rust, D and Nim, as well as .Net Core 2.0 applications. (Android and Windows 10 IoT are not supported.) Due to the built-in Broadcomm VideoCore IV GPU, the ComfilePi can even render real-time 3D graphics. CODESYS can be used on the ComfilePi by installing one or more of the CODESYS Raspberry Pi Control Modules. CODESYS is a development environment for programming controller applications according to the international industrial standard IEC 61131-3. Made in South Korea by Comfile Technology, ComfilePi products are available now from the distributor Saelig.
I/O CARDS FOR RPi
For its part, Sequent Microsystems makes a variety of Raspberry Pi-compatible I/O boards serving diverse applications. In July, the company Kickstarted a stackable HAT called the Mega-RTD. Resistance Temperature Detector (RTD) sensors, which are used for highly precise temperature measurements in industrial and laboratory systems, can be found on embedded systems. Sequent Microsystems won Kickstarter funding for a Mega-RTD HAT that can be stacked to provide the Raspberry Pi with up to 64 RTD channels. Shipments are due in October.
Sequent’s next Raspberry Pi offering, listed on its website now as “coming soon,” is a Raspberry Pi stackable card for industrial automation under the product code MEGA-IND (Figure 5). The board will be the company’s second-generation industrial automation card, and is designed to bring to Raspberry Pi all the necessary inputs and outputs to implement complex industrial automation projects, says Sequent.
The MEGA-IND features four optically isolated digital inputs with status LEDs, four 0V – 10V or 0 to ±10V analog inputs and four optically isolated 4-20mA inputs. You also get four optically isolated open drain 24V/4A outputs, four 0-10V analog outputs and four 4-20mA analog outputs. The card provides TVS protection on all inputs.
Other features of the MEGA-IND include RS485 and CAN ports, 24VDC power supply, on-board hardware watchdog and on-board resettable fuse. The board provides a real time clock with battery backup, pluggable connectors, support for eight-level stacking with all mounting hardware included. Command line and Python driver support is provided.
PICO-ITX WITH RPi EXPANSION
Some embedded board vendors have taken advantage of Raspberry Pi’s open specifications to create their own SBCs that include Raspberry Pi expansion support. That opens the door to, for example, more rugged SBC offerings that can work with the same HATs as Raspberry Pi SBCs. Along exactly those lines, in August ICP (Industrial Computer Products) Germany released an i.MX8M-based Pico-ITX SBC that it’s positioning as an industrial replacement for a Raspberry Pi SBC.
The 100mm × 72mm board serves up a 1.5GHz NXP i.MX8M in either quad- or dual-core versions. Memory options include 1GB, 2GB or 4GB LPDDR4 SDRAM with 1600MHz clock rate. There’s a standard Mini-PCIe with PCIe and USB signal. A Raspberry Pi-compatible 40-pin header with GPIO signal is available as an expansion slot along with an API library.
In the basic version, ND108T comes with HDMI 2.0 with 4K resolution, GbE, 2x USB 3.0, 1x USB 2.0, 1x RS-232/422/485 and audio line-out and mic-in. A USB 2.0 OTG and a UART are available for programming and debugging. For mass storage you get an eMMC with 8GB, 16GB or 32GB storage and a microSD slot.
The basic version can be upgraded if required, says ICP. Dual GbE or other display connectors like LVDS or Display Port are optional. The ND108T operates from a 12V power supply in a temperature range of 0 to 60°C and complies with the CE/FCC Class B standard. Operating system support includes Board Support Packages (BSPs) for Yocto Sumo and Android 9 Pie, both with Linux Kernel 4.14.98.
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BOX-LEVEL RPi SYSTEM
Support for Raspberry Pi appears to have even infiltrated the box-level embedded system realm. As reported by Circuit Cellar’s sister website LinuxGizmos, in July, Advantech launched what appears to be its first Raspberry Pi-compatible system. The $90, 100mm × 70mm × 33mm Uno-220 IoT gateway is designed to be powered by a bring-your-own Raspberry Pi 4 Model B (Figure 6). The Uno-220 exposes all the ports on the RPi 4 and adds a custom HAT add-on with serial and GPIO connectivity. The system ships with an 8GB microSD card that is preconfigured with a Raspberry Pi OS based AdvRaspbian stack. AdvRaspbian is said to offer plug-and-play installation with the Raspberry Pi 4. The source code is also available on GitHub.
External access is provided for the new RS-232/485 port with auto direction control and a terminal block interface. There are also 4x GPIOs and inside the box is a real-time clock with battery installed on the HAT. TPM 2.0 is available on request. Standard options are wall- and stand mounts, while DIN-rail mounting is optional. The system ships with all necessary screws to integrate the Raspberry Pi.
The aluminum-built IoT gateway is protected per IP40 specs, supports 0 to 50°C temperatures, and provides 10-95% RH at 40°C, non-condensing humidity resistance. The enclosure’s improved heat dissipation and electrostatic discharge protection provides the optimum protection for Raspberry Pi SBCs, according to Advantech.
FPGA-BASED RPi ZERO CLONE
As discussed earlier, the open-spec nature of Raspberry Pi makes it ripe for board developers to design clones of the SBCs. Along just those lines, in August Trenz Electronic launched its open-spec ZynqBerryZero, a pseudo-clone of the Raspberry PI Zero SBC with a Zynq-7010 Arm/FPGA SoC, a microSD slot, dual micro-USB, mini-HDMI, CSI-2 and 40-pin GPIO (Figure 7).
In 2017, Trenz Electronic rolled out its ZynqBerry SBC from, which combines a Xilinx Zynq-7010 FPGA SoC with a Raspberry Pi. Now, this new ZynqBerryZero (TE0727) SBC takes a similar approach, but this time imitating the Raspberry Pi Zero. The 65mm × 30mm SBC offers a 40-pin GPIO header that can load Raspberry Pi HATs that support the Zero.
The ZynqBerryZero trades out the Zero’s 1GHz, Arm11-based Broadcom BCM2836 for the Zynq-7010, which combines dual 667MHz Cortex-A9 cores with an FPGA with 28K logic cells, compared to 85K for the Zynq-7020. The SBC comes with 512MB DDR3L DRAM, 16MB flash and a microSD slot. The SBC’s coastline ports are limited to a mini-HDMI Type-C port, dual micro-USB 2.0 ports, an OTG port and a port for JTAG/UART debugging and 5V power input. The 0 to 70°C tolerant board is also equipped with a 40-pin header with 26x GPIOs and a MIPI-CSI-2 camera connector.
IoT GATEWAY FOR RPi
IoT gateways are yet another area that has embraced the Raspberry Pi phenomenon. With that in mind, in July Hilscher released its Raspberry Pi based netPI Real-Time Ethernet gateway. The netPI series is based on an industrial-ready, customized Raspberry Pi 3 design made to run any custom applications in edge automation (Figure 8). The model RTE 3 comes with Hilscher’s multiprotocol netX SoC additionally implementing all popular Industrial Ethernet networks. With their powerful RPi 3 1.2GHz quad-core Arm CPU, the platforms are ready-made for any demanding Cloud, Industry 4.0 and Industrial IoT (IIoT) application.
The model netPI RTE 3 includes two extra Industrial Ethernet ports extra to connect to systems such as PROFINET, EtherNet/IP and others, as supported by netX. An expansion slot at the unit’s bottom accepts extension modules made for sensor/actuator level communications such as RFID, digital I/Os, others or your own custom boards.
To meet EMC standards EN 55011 and IEC 61000, netPI is housed in a robust metal chassis and uses two additional PCB layers compared to a standard Raspberry Pi 3 SBC. The radio antenna extends beyond the chassis for improved wireless coverage. A hardware Real-Time Clock with a supercapacitor as backup power source is supported. A nonvolatile auxiliary ferroelectric memory (FeRAM) guarantees high endurance for data to be rewritten billions of times (Model RTE 3).
The netPI hosts an AppArmor-secured Yocto Linux build. By design, the system software complies with the IEC 62443 cybersecurity standard for automation and control systems. User access is granted via web browsers over https-secured connections. The device boots secure and allows system updates with Hilscher integrity-checked software only. 
RESOURCES
Advantech | www.advantech.com
Avnet | www.avnet.com
Hilscher | www.hilscher.com
ICP Germany | www.icp-deutschland.de
Infineon Technologies | www.infineon.com
Measurement Computing| www.mccdaq.com
Renesas Electronics | www.renesas.com
Saelig | www.saelig.com
Sequent Microsystems | www.sequentmicrosystems.com
SparkFun | www.sparkfun.com
Trenz Electronic | www.trenz-electronic.de
PUBLISHED IN CIRCUIT CELLAR MAGAZINE • OCTOBER 2020 #363 – Get a PDF of the issue
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Jeff served as Editor-in-Chief for both LinuxGizmos.com and its sister publication, Circuit Cellar magazine 6/2017—3/2022. In nearly three decades of covering the embedded electronics and computing industry, Jeff has also held senior editorial positions at EE Times, Computer Design, Electronic Design, Embedded Systems Development, and COTS Journal. His knowledge spans a broad range of electronics and computing topics, including CPUs, MCUs, memory, storage, graphics, power supplies, software development, and real-time OSes.
