Although the Pi A+, B+, and Model 2-B are used for all of our projects, nothing covered in this book precludes the use of the older A and B models. The Pi you purchased might be sourced from many different suppliers. There are some critical differences that you need to be aware of if you plan to use the Pi for a hobby project or education tool:
|
Model type |
GPIO header |
SD type |
Audio / Composite video |
|---|---|---|---|
|
Raspberry Pi A and Pi B |
26 pins |
standard |
Separate TRS and RCA connections |
|
Raspberry Pi B+, A+ and Pi Model 2-B |
40 pins |
micro |
Combined into a single TTRS connector |
If you compare other revisions of the Pi with the following image, you will notice that there are some orientation and position changes for connectors and different mounting holes on the A+, B+, and Model 2-B as compared to the A and B models:
We suggest that you consider a complete kit of parts as a good starting point—if you haven't already bought your Pi. In particular, there are kits from Canakit.com for around $90. The kit includes everything needed for a new Pi project designer.
It is important to know that an insufficient power supply current capability could result in an installation that is unreliable and proves hard to diagnose when problems occur. It's OK to have a power supply capable of delivering more current than needed; the system only draws the current it requires.
The most common guidance for the Pi B is a 5-Volt power supply providing between 700 mA and 1 Amp and for the Pi B+ and Model 2-B, between 600 mA and 2 Amp. The higher power requirements for the Pi B+ and Pi 2-B (four USB connections) enable connection to a wide range of USB peripherals such as USB disks, portable printers, scanners, and so on.
Note
Note that the Pi B+ and Pi 2-B have internal current limits of 600 mA set on the USB ports; exceeding the current will power off the port momentarily. The USB 2.0 specification recommends a maximum peripheral device current specification of 500 mA. You should ensure that heavy current peripherals are supported via an externally powered USB hub for the best reliability.
We used an AmazonBasics seven-port USB hub (see the following image) which has two ports that can provide over 1.2 Amp each, and five more ports that can provide up to 500 mA per port. It has a power supply rated for 5V at 4A, which cannot support maximum power on every port simultaneously (rarely required in any realistic configuration).
Our multi-Pi development environment is shown in the following image:
Before you can decide how to power your Pi, you must determine the highest level of current required to ensure that your devices can be properly supported in the configuration. We will continue to discuss power issues as they arise throughout the projects.
Our Pi is powered by a single AmazonBasics hub. The Pi and the hub are attached to a small piece of medium-density fibreboard (MDF) board using Velcro, which is an easy way to connect peripherals while designing a project. There is a WiFi adapter, keyboard, and mouse plugged into the hub. We normally connect via an Ethernet network interface, which facilitates the testing of a broader range of networking scenarios. You will notice in our configuration that a Pi-cam is connected and that we have a Microsoft webcam at the top of the right-hand side speaker.
A development desktop power/USB configuration like the one we showed in the preceding image will provide you with a stable development platform for our project designs. Of course, most final designs may require only the four USB ports on the motherboard and consume as little as 300 mA on average. The following list is the minimum configuration required to complete the projects in this book: