Hardware Reference
In-Depth Information
The pedals are connected to power (+5 V) and wired to the MCP23008s. The digital
inputs are also connected to pull-down resistors to clear out digital noise.
The Raspberry Pi is connected to the I2C series and also to a Din5 connector (the
industry standard for MIDI connections). The Din5 is mounted on a Sparkfun MIDI
shield kit, mostly chosen for availability and ease of use.
A powered USB hub is also part of the hardware installation. The hub has one device
attached, a wireless networking dongle. The powered hub is necessary because the
Raspberry Pi does not carry enough current to reliably power most wireless dongles
(see
Hack #08
).
Why Wireless TCP/IP?
The wireless networking is part of a software choice made fairly early in the
implementation cycle. Initial external control relied on the Raspberry Pi's
onboard Ethernet connection, which implies a requirement for networking
infrastructure. However, one facet of the Alcyone's potential use is stage
work, and at many theaters, networking is spotty if existent at all.
The simplest solution involves the Alcyone serving as its own wireless ac-
cess point, meaning that it provides its own networking infrastructure.
An alternative would be to avoid TCP/IP altogether. Bluetooth is another
messaging protocol, one designed for device-to-device communications,
particularly for short messages. Bluetooth devices can also be designed for
low-power usage. However, this means writing a custom Bluetooth client
for every possible client platform.
The wireless on the Raspberry Pi is configured as an access point so the Alcyone can
serve as its own networking infrastructure. It has its own network SSID and security.
The external client has to use this access point in order to control the Alcyone.
Not only does this avoid reliance on what might be inconsistent or nonexistent net-
work services, it also limits the amount of traffic that competes for the client, and it
also allows us to use a consistent IP for the Alcyone (as opposed to guessing what
valid address the Alcyone happens to receive from the network infrastructure).
