Raspberry Pi Fog Class Devices Hardware Review

Hardware boards (depending on the manufactured model) contain interfaces: Ethernet, Bluetooth, WiFi, USB, AUDIO, HDMI and GPIO ports ^[1]. The Raspberry Pi boards have evolved through several versions varying in memory capacity, System on Chips (SoC) and processor units. The first generation models of Raspberry Pi used the Broadcom BCM2835 (ARMv6 architecture) based on a 700 MHz ARM11176JZF-S processor and VideoCore IV graphics processing Unit (GPU). Models Pi 1 and B+, developed later, use the five-point USB/Ethernet hub chip, while the Pi 1 Model B only contains two. The Pi Zero USB port is connected directly to the SoC and uses the (OTG) micro USB port.

The first Raspberry Pi 2 models use the 900 MHz Broadcom BCM2836 SoC 32-bit quad-core ARM Cortex-A7 processor with a shared 256 KB L2 cache. After these earlier models, the Raspberry Pi 2 V1.2 has been upgraded to a Broadcom BCM2837 SoC equipped with a 1.2 GHz 64-bit quad-core ARM Cortex-A53 processor. Next, the Raspberry Pi 3 series uses the same SoC. They use the Broadcom BCM2837 SoC with a 1.2 GHz 64-bit quad-core ARM Cortex-A53 processor with a 512 KB shared L2 cache. The Raspberry Pi 3B+ uses the same processor (BCM2837B0) running at 1.4 GHz. The Raspberry Pi 4 is based on Broadcom BCM2711, a quad-core Cortex-A72 64-bit SoC at 1.5 GHz. Raspberry Pi 5 works with a maximum of 2.4GHz. The following Raspberry Pi generations will be increasingly powerful, but their power consumption is also rising, forcing developers to use CPU and GPU heatsinks and more robust power sources.

The initial Raspberry Pi boards were designed with 128 MB RAM, which was allocated between the GPU and CPU by default. In the newer edition (including Model B and Model A), the RAM was extended to 256 MB and split into the regions. The default split was 192 MB (RAM for CPU), which is sufficient for standalone 1080p video decoding or 3D modelling. Models B with 512 MB RAM initially, memory was split into files released (arm256_start.elf, arm384_start.elf, arm496_start.elf) for 256 MB, 384 MB and 496 MB CPU RAM (and 256 MB, 128 MB and 16 MB video RAM). The Raspberry Pi 2 and 3 are shipped with 1 GB of RAM. The Raspberry Pi 4 can have 1, 2, 4 or even 8 GB of RAM. The Raspberry Pi Zero and Zero W contains 512 MB of RAM.

The Model A, A+ and Pi Zero have no dedicated Ethernet interface and can be connected to a network using an external USB Ethernet or WiFi adapter. In Models B and B+, the Ethernet port is built-in to the USB Ethernet adapter using the SMSC LAN9514 chip. The Raspberry Pi 3 and Pi Zero W (wireless) models are equipped with 2.4 GHz WiFi 802.11n (150 Mbit/s) and Bluetooth 4.1 (24 Mbit/s) based on Broadcom BCM43438 FullMAC chip. The Raspberry Pi 3 also has a 10/100 Ethernet port. The latest Raspberry Pi 4 contains a dual band 2.4 / 5 GHz WiFi network adapter (IEEE 802.11ac), Bluetooth 5.0, and Gigabit Ethernet.

The Raspberry Pi may be controlled with any generic USB keyboard and mouse. It can also use USB storage, USB to MIDI converters, and virtually any other device/component which is USB compatible. Other peripherals can be attached through the various pins and connectors on the surface of the Raspberry Pi.

The video controller supports standard modern TV resolutions, such as HD and Full HD, and higher. It can emit 640 × 350 EGA; 640 × 480 VGA; 800 × 600 SVGA; 1024 × 768 XGA; 1280 × 720 720p HDTV; 1280 × 768 WXGA variant; 1280 × 800 WXGA variant; 1280 × 1024 SXGA; 1366 × 768 WXGA variant; 1400 × 1050 SXGA+; 1600 × 1200 UXGA; 1680 × 1050 WXGA+; 1920 × 1080 1080p HDTV; 1920 × 1200 WUXGA. Higher resolutions, such as up to 2048 × 1152, may work or even 3840 × 2160 at 15 Hz. Although the Raspberry Pi 3 does not include H.265 hardware decoders, the CPU is more powerful than its predecessors, potentially fast enough for software decoding H.265-encoded videos. The Raspberry Pi 3 GPU runs at a higher clock frequency – 300 or 400 MHz, compared to 250 MHz in previous versions. The Raspberry Pi can generate 576i and 480i composite video signals, as used on old-style (CRT) TV screens and less-expensive monitors through standard connectors – either RCA or 3.5 mm phono connector, depending on the models. The television signal standards supported are PAL-BGHID, PAL-M, PAL-N, NTSC and NTSC-J. The Raspberry Pi 4 has two micro HDMI connectors that support 4K displays with a refreshing rate of 60Hz.

None of the current Raspberry Pi models has a built-in real-time clock. Developers who need real clock time in their project can retrieve the time from a network time server (NTP) or use the external RTC module connected to the board via SPI or I²C interface. To save the file system consistency, the Raspberry Pi automatically saves time on shutdown and reloads time at boot. One of the best RTC solutions for keeping the proper board time is to use the I²C DS1307 chip containing a hardware clock with a battery power backup.

Following tables 1, 2, 3, 4 and 5 present technical details of the RPI fog class IoT devices.

As for today, on the market, a few models of Raspberry Pi boards are available, from tiny ones to more powerful ones. Users can choose the right board to fit the price and functionality of their project development needs. Figures 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10, are presenting Raspberry Pi models, starting from the simplest and finishing on the most advanced and most modern ones.

Each Raspberry Pi model is equipped with a standard 34/40-pis male connector containing universal GPIO ports, VCC 3.3/5V, GND, CLK, I2C/SPI bus pins, which developers can use to connect their external sensors, switches and other controlled devices to the Raspberry Pi board and then program their behaviour within the code loaded to the board.

• Raspberry Pi 1 Models A+ and B+, Pi 2 Model B, Pi 3 Model B and Pi Zero (and Zero W) GPIO J8 have a 40-pin pinout. Raspberry Pi 1 Models A and B have only the first 26 pins.

• Model B rev. 2 also has a pad (P5 on the board and P6 on the schematics) of 8 pins, offering access to 4 GPIO connections.

Each Raspberry Pi model is equipped with the standard, mini or micro HDMI port, which allows the user to connect the monitor or TV set to the board. The electronic schematic is shown in the picture.

Raspberry Pi boars Zero, 1, A+, 2, 3, 4 and 5 are equipped with a Camera interface (CSI) port, allowing the user to connect the CCD camera following the MIPI standard.

Raspberry Pi boards 2 to 5 have an LCD Display interface(DSI) port, allowing the user to connect the LCD touch display to the board. The official Raspberry Pi LCD touch display shown in the figure below is 800 x 480 dpi 7“ in size and can be connected to the Raspberry board using the DSI interface. Such an assembly can be used in the projects to display a controlling application view, and the ability to handle fingers and a touchscreen controls the project behaviour. The LCD can be mounted in portrait/landscape orientation, fitting the best user needs.

Raspberry PI models Zero, 1, A+, 2, 3, 4 and 5 contain USB ports (from 1 up to 4), and all but Zero also have a LAN port for TCP/IP network connections. These ports can be used for mouse/keyboard connection or if the software has the appropriate driver installed to handle other USB devices.

Since generation 4, devices are equipped with 2 USB 3.0 ports as in figure 18.

Starting with Raspberry 3B+, the Ethernet port is a gigabit one that can reach up to 1Gbps, theoretically. Prior 3B (including) it is fast Ethernet, 100Mbps.