VOISS - Interfaces
Written by Rich Morin.
Precis: an overview of VOISS (etc) interfaces
Note: As of early 2020, the VOISS project and F123Light were discontinued. For details, see VOISS - Status.
The “full-size” RasPi models, as used in the VOISS systems, support an amazing range of external interfaces.
Here are some quick summaries of the most popular interfaces, with the usual links for more detailed information …
Note: You may be tempted to use other external interfaces in preference to the default approaches. However, I recommend that you begin with the default interfaces. Once your system is working reliably with these, you can try swapping in devices that use alternative interfaces. If this doesn’t work, you can always get back to a working setup.
The RasPi has a single, miniature size (1/8”, 3.5 mm) stereo connector. This supplies stereo analog audio and is typically used to support headphones. Bluetooth is also commonly used for audio input and output. The HDMI “video” interface can provide high-quality digital audio output. Finally, the RasPi’s general-purpose input/output (GPIO) pins can be used to generate digital audio by means of pulse-code modulation (PCM).
Bluetooth supports short-range wireless connections, roughly 30 feet or 9 meters. It tends to be used for common peripheral devices, such as headphones, keyboards, and mice. However, it can also be used to talk to some home appliances, such as the Anova Precision Cooker. Until a computer and device are “introduced” to each other, they will generally ignore each other’s presence. This provides a modicum of security in public places.
The RasPi supports Ethernet over twisted pair. This provides wired Ethernet connectivity which is typically use to talk to other computers. Because Ethernet access is provided through a physical interface, typically controlled by a network administration staff, security is seldom much of an issue.
The RasPi’s general-purpose input/output (GPIO) interface is supplied thtough a 40-pin (2x20) set of “header” pins. Although the pins can be addressed, connected and used individually, the most convenient way to wire them up is by using a female header socket. This may be at the end of a ribbon cable (e.g., going to another board) or mounted on the bottom of a Hardware Attached on Top (HAT).
For an easy way to get started on wiring up electronic devices, consider adding a “breakout board” of some sort. I really like Seeed’s Grove System, which uses polarized, four-pin connectors and ribbon cables. Each connection provides 5 VDC power and ground leads, as well as two other signals, taken from the GPIO header. using a HAT and a set of Grove boards lets you avoid a wide range of wiring errors (and consequent difficulties).
I have the GrovePi Plus HAT, which has 15 sockets and passes through 26 pins from the GPIO header (e.g., for use with other HATs). Seeed sells more than 100 “Groves”, supporting a variety of sensor, actuator, and interface functions. They aren’t terribly expensive and work with various processor types. So, you can trade them back and forth with other aspiring hardware hackers.
The RasPi provides four USB sockets. These can support short-range wired connections, roughly 12 feet or 3 meters (but this can be extended). It tends to be used for common peripheral devices, such as headphones, keyboards, mice, and printers. However, it can also be used to talk to oddball devices such as cameras, data storage, and tire pressure gauges. In fact, it can be used to transfer data between pairs of computers.
USB is commonly used as a convenient source of 5 VDC power. Outlets are easy to find and come in many forms. Some devices (e.g., charging stations, vehicle adapters, wall warts) are explicitly designed to supply USB power. “USB Master” devices (e.g., computers) supply power as part of their duty to support “USB Slave” devices (e.g., headphones, keyboards).
Because the RasPi is powered by means of a Micro-USB socket, you may be tempted to hook it up to one of these power sources. Don’t do that! Aside from the dangers of poorly controlled and filtered power, the 3B+ needs more power than most of these sources can provide. See below for more information on this topic.
The RasPi has a pair of ribbon-cable sockets that support a directly-attached camera and/or display screen. The cable distance is very limited (about a foot), but it might serve well for screencasts and online video chat. USB can also be used to attach cameras and some display screens. The RasPi’s Type D (micro) HDMI socket is commonly used to provide high-resolution digital audio and video. Typical output devices include display screens, projectors, and television sets.
Wi-Fi supports longer-range wireless connections, roughly 100 feet or 30 meters. It tends to be used to other computers, either directly or through intervening links (e.g., routing hardware). With varying degrees of security, Wi-Fi can be used to create or join networks. For example, one RasPi might browse a website provided by another.