1. The Raspberry Pi

Warren Gay¹

(1)

St. Catharine’s, Ontario, Canada

The Raspberry Pi is amazing at two levels—the advanced functionality that you get in a credit card-sized SBC (Single Board Computer) and its price. Even with today’s Pi competitors, the Raspberry Pi reigns supreme because few can beat its price. Further, it enjoys great software and community support.

Price is an important advantage of the Pi that competitors don’t always appreciate. Hobbyists and makers are applying the Pi in new and sometimes risky ways. Someone starting out doesn’t want to lose their SBC because of a rookie mistake. At the low Pi price point, the loss can be absorbed without losing heart. Imagine a student buying an Intel Joule¹ (when it was offered) for $349 USD and toasting it by accident. That would be enough to make most people give up right there! Price allows everyone to proceed fearlessly in their learning.

SBC Inventory

Before considering the details about the resources within the Raspberry Pi, it is useful to take a high-level inventory. In this chapter, let’s list what you get when you purchase a Pi.

Within this book, you’ll be examining each resource from two perspectives:

The hardware itself—what it is and how it works
The driving software and API behind it

In some cases, the hardware will have one or more kernel modules behind it, forming the device driver layer. They expose a software API that interfaces between the application and the hardware device. For example, applications communicate with the driver by using ioctl(2) calls, while the driver communicates with the I2C devices on the bus. The /sys/class file system is another way that device drivers expose themselves to applications. You’ll see this when GPIO (general purpose input/output) is examined in Chapter 12.

There are some cases where drivers don’t exist in Raspbian Linux, requiring you to use a “bare metal” approach. An example of this is creating PWM signals using software. By mapping the GPIO registers into the application memory space, the desired result can be obtained directly from the application program. Both direct access and driver access have their advantages and disadvantages.

So while the summary inventory simply lists the hardware devices, you’ll be examining each resource in greater detail in the chapters ahead.

Models

The hardware inventory is directly affected by the model of the unit being examined. Several models have been produced over the years, starting with the Model B, followed by the Model A. Since then, several other units have become available and these are summarized in Table 1-1. Much more detail can be seen online.²

Table 1-1

Summary of the Raspberry Pi Models

Model	Introduced	Price	CPU	SoC	Misc
Model A	Feb 2013	$25	ARMv6Z	BCM2835	32-bit
Model A	Nov 2014	$20	ARMv6Z	BCM2835	32-bit
Model B	April 2012	$35	ARMv6Z	BCM2835	32-bit
	July 2014	$25	ARMv6Z	BCM2835	32-bit
Model B 2	Feb 2015	$35	ARMv7-A	BCM2836	Quad 32-bit
Model B 2 (1.2)	Oct 2016	$35	ARMv8-A	BCM2837	Quad 32/64-bit
Model B 3	Feb 2016	$35	ARMv8-A	BCM2837	Quad 32/64-bit
Model B 3+	Mar 2018	$35	ARMv8-A	BCM2837B0	Quad 32/64-bit
Compute Module 1	Jan 2016	$30	ARMv6Z	BCM2835	32-bit
Compute Module 3	Jan 2017	$30	ARMv8-A	BCM2837	Quad 64-bit
Compute Module 3 Lite	Jan 2017	$25	ARMv8-A	BCM2837	Quad 64-bit
Zero (1.2)	Nov 2015	$5	ARMv6Z	BCM2834	32-bit
Zero (1.3)	May 2016	$5	ARMv6Z	BCM2834	32-bit
Zero W	Feb 2017	$10	ARMv6Z	BCM2834	Wireless 32-bit

Raspberry Pi Model B

Figure 1-1 illustrates a Raspberry Pi Model B, generation 1. This board was released around April 2012 for $35 USD. Notice that it used the large SDHC (secure digital high capacity) card, shown at left in the photo. The socket underneath is illustrated in Figure 1-2. The GPIO strip was a 26-pin header at the time, the same as the Model A that followed. There was also a 4x2 header labeled P5, which had power, ground, and four more GPIO pins.

../images/326071_2_En_1_Chapter/326071_2_En_1_Fig1_HTML.jpg — Figure 1-1
Raspberry Pi Model B (top side), generation 1

The ARM architecture used is ARMv6Z. The single 32-bit core ran at 700 MHz, using 256 MB of SDRAM. In May 2016 this was increased to 512 MB. The board includes 2 USB ports, a 15-pin MIPI camera interface, a LCD MIPI interface, HDMI and RCA composite video outputs, 3.5 mm audio jack, and GPIOs. The network interface consists of a 10/100 Mbit/s Ethernet adapter.

../images/326071_2_En_1_Chapter/326071_2_En_1_Fig2_HTML.jpg — Figure 1-2
Raspberry Pi Model B (bottom), generation 1

The power rating was approximately 700 mA (3.5 W) taken from the Micro-USB connector or header strip.

Raspberry Pi 2 Model B

The Raspberry Pi 2 Model B came out February 2015 for $35 USD. This model uses the ARMv7A 32-bit architecture. The main improvement was the support of four CPU (central processing unit) cores, running at 900 MHz. Another improvement was the 1 GB of SDRAM, allowing for larger application mixes. Figure 1-3 illustrates the top side of the pcb, while Figure 1-4 shows the bottom.

Other notable changes included the Raspberry Pi standardized 40-pin header strip for GPIO. Four USB ports were provided and the mounting holes were moved on the pcb (printed circuit board).

../images/326071_2_En_1_Chapter/326071_2_En_1_Fig3_HTML.jpg — Figure 1-3
The top side of the Raspberry Pi 2 Model B

The board also uses the Micro-SDHC slot for file storage. Figure 1-3 shows it sticking out from under the pcb at the middle left. Power consumption drops to 220 mA when idle (1.1 W) but jumps up to 820 mA (4.1 W) under stress. This required a larger power adapter to properly feed the unit.

../images/326071_2_En_1_Chapter/326071_2_En_1_Fig4_HTML.jpg — Figure 1-4
The bottom side of the Raspberry Pi 2 Model B

Raspberry Pi 3 Model B

February 2016 brought with it the arrival of the Raspberry Pi 3 Model B, again for $35 USD. This offered the ARMv8-A 64/32-bit architecture. The quad cores ran at a brisk 1.2 GHz with the provided 1 GB of SDRAM. Another gift was the addition of IEEE 802.11n-2009 wireless support and Bluetooth 4.1. Figure 1-5 illustrates the top side of the pcb while Figure 1-6 shows the bottom.

Power consumption is 300 mA (1.5 W) when idle but increases to 1.34 A (6.7 W) under stress. The figures show a heat sink added to the CPU, which is not included. Adding the heat sink prevents the core from reducing the clock speed to regulate the temperature.

../images/326071_2_En_1_Chapter/326071_2_En_1_Fig5_HTML.jpg — Figure 1-5
Top side of Raspberry Pi 3 Model B

../images/326071_2_En_1_Chapter/326071_2_En_1_Fig6_HTML.jpg — Figure 1-6
Bottom side of Raspberry Pi 3 Model B

Raspberry Pi 3 Model B+

This model arrived in March 2018, again for the great price of $35 USD. It is a 64-bit, 1.4 GHz quad core, with 1 GB of SDRAM. The network port supports 10/100/1000 Mbits/s Ethernet, although the top speed is limited to about 300 Mbit/s because of its internal use of the USB hub. The wireless support now included 802.11ac for dual band 2.4/5 GHz operation. Bluetooth was upgraded to Bluetooth 4.2 LS BLE.

Power consumption is 459 mA (2.295 W) at idle and increases to 1.13 A (5.661 W) under full stress. Notice the metal cap on the CPU chip in Figure 1-7. This helps to dissipate the heat without requiring a heat sink (although it may still be beneficial to use one). The underside of the pcb is shown in Figure 1-8.

../images/326071_2_En_1_Chapter/326071_2_En_1_Fig7_HTML.jpg — Figure 1-7
Top side of Raspberry Pi 3 Model B+

../images/326071_2_En_1_Chapter/326071_2_En_1_Fig8_HTML.jpg — Figure 1-8
Bottom side of Raspberry Pi 3 Model B+

Raspberry Pi Zero

Not every maker project requires the full resources of a 64-bit quad core and 1 GB of SDRAM. The first Raspberry Pi Zero came out in November 2015 and later upgraded in May 2016. At a unit price of $5 USD, it makes an ideal SBC for many small projects.

The Zero is an ARMv6Z architecture (32-bit) device and runs the single core at 1 GHz. SDRAM is limited at 512 MB, which is still very sufficient for most projects. The first Zeros lacked the MIPI camera interface, which was added in the 2016 revision.

To save on cost, there is no soldered header strip or connector. There are also marked points on the pcb for the composite video, should the end user need it. The HDMI output is provided through a Mini-HDMI connector and the stereo audio is provided via PWM (Pulse Width Modulation) GPIO. There is also no wired Ethernet port on the Zero. It can be provided by using the one Micro-USB port and an Ethernet adapter.

The power is provided through the other Micro-USB connecter, and the consumption at idle is 100 mA (0.5 W), and 350 mA (1.75 W) under stress. Figures 1-9 and 1-10 illustrate the Raspberry Pi Zero and the Raspberry Pi Zero W.

../images/326071_2_En_1_Chapter/326071_2_En_1_Fig9_HTML.jpg — Figure 1-9
The top side of the Raspberry Pi Zero (at bottom) and the Raspberry Pi Zero W (at top)

../images/326071_2_En_1_Chapter/326071_2_En_1_Fig10_HTML.jpg — Figure 1-10
The bottom side of the Raspberry Pi Zero (bottom) and the Raspberry Pi Zero W (at top)

Raspberry Pi Zero W

The “W” in Raspberry Pi Zero W name is a giveaway that this is enhanced by the wireless capability, over the Zero. It is priced at $10 USD. The wireless standards supported are 802.11n and Bluetooth 4.1. Like the Zero, the Zero W has no wired Ethernet connector and only one Micro-USB port (the other is used for power only). Having the WIFI (WIFI is a trademark of the Wi-Fi Alliance) access greatly increases the device’s communication versatility.

Which Model?

The question that naturally arises is “which model to buy?” The answer is much like buying a car—it depends. If you are looking for a cheap computer that you can attach keyboard, mouse, and monitor to, then buy the most powerful device, like the Raspberry Pi 3 Model B+. Another class of project involving AI (artificial intelligence) or video recognition is another case for powerful hardware.

For building something that must weather outside and take photos of birds in a nest, then the Raspberry Pi Zero W with WIFI connectivity seems appropriate. There are perhaps other projects that don’t require network access at all, where the lowest price like the Zero applies. The best news is that you have a wide range of choices at low prices.

Table of Contents for Advanced Raspberry Pi: Raspbian Linux and GPIO Integration