Good question. I researched about 50 existing networks
from simple diode-mixing to full-on systems like Lonworks. Not one
of them allowed the right combination of low-priced components, simplicity
and robustness with simple plug-and-play nodes, tiny hardware requirements,
open source, and suitability for any processor including interpreted
processors like the Picaxe.
Originally because it was designed for owner-built
motorhomes that are mostly constructed from old busses, but also because
a "bus" is one of the many wiring topologies usable and
of course it is a network. The other option was YABAN (Yet Another
Bloody Async Network).
BUSnet is no longer a "bus" topology but
the name will stay.
How many wires does BUSnet need?
The standard RS-485 connection between nodes requires
four wires for data, and optionally two more for the earth return
and power. Other physical layers may use fewer wires, for example
RS-232 would only need 2 data signals.
Why not use wireless?
Mostly because of the expense and party because
of perceived reliability issues. A bidirectional wireless interface
will cost maybe $15-20 or more per Node
and I've not had much luck with wireless devices over the years.
Having said that a wireless gateway is a good idea
in some cases, such as a display in a car for a network on a towed
caravan. The publish/subscribe model actually makes it easy to have
two or more wired networks all connected with wireles links
Is BUSnet just for those fancy Winnebagos?
Definitely not. Although quite capable of handling a large sophisticated
system such as may be found in a 40-foot coach, BUSnet was originally
designed for retrofitting to old busses (hence the name in part) and
very small products are being designed with just a few Points for
use in campervans and 4x4s.
BUSnet is also no longer just for RVs, it's designed for any monitoring
and control application up to light-industrial use.
Do I have to write 100s of lines of complicated
No, this has already been done and the protocol code resides in the
BUSnet PIPE chip. As a node developer you don't have to write a single
line of "network" code. It depends on the level of robustness
The spec is open though, so you can write the protocol if you want
to. The source code is open as well, so you can use that as a start
if you want to do your own thing.
You can also use a PIPE chip in stand-alone mode. This give 6 digital
IOs, 5 analogue inputs, and I2C and SPI interfaces. Therefore you
can build a node with no programming required at all.
Can I use any processor with BUSnet?
Yes, there is only one basic requirement of your processor, the ability
to talk to a peripheral chip (the PIPE) using I2C.
What size are BUSnet Nodes?
Any size you like, current nodes are designed for the MAXX system
which has IO nodules that are 41x37mm.
A node with no connectors (using flying leads) can be made as small
What is the simplest possible Node hardware?
If you write the protocol code yourself (protocol
and application code are therefore in a single chip) a fully working
node can be built with three IC's (a processor and two RS-485 transceivers),
two capacitors, and a diode bridge. If you don't write the protocol
code add another processor for the application.
How do I develop BUSnet node hardware?
The simplest way is to get a PIPE chip and add the IO and network
interface. At the next level up you add your own processor to the
board and use the PIPE as a peripheral.
I will probably produce a prototype PCB as well, this will have the
PIPE and line interface and a pad array for prototyping.
How do I write BUSnet application software?
Use the same tools you already use to develop embedded systems. You
have to be able to talk standard I2C to a PIPE interface chip.
These PIPEs sound important, do I have to buy
them from you?
No, there are three basic options. Using the published specs you
can write your own protocol handler on your own chip, if you are using
LPC1227 processors you can download the source code and program your
own chips. Finally of course you can buy pre-programmed chips from
me or anyone else selling them.
How come a Node doesn't need switches for address
At any time a node can request an address map from the network. New
nodes do this then take a free address. Once the node has an address
map it knows what addresses are free and it chooses one of those them.
Does BUSnet need any fancy cables or connectors?
No, BUSnet uses any standard 6 or 8-way cable.
What's the story
with licensing then?
BUSnet is a open source project aimed at hobbyists and small business
with a need to implement small monitoring and control networks. Everything
about BUSnet from the nonproprietary components used to the licensing
is designed to make the entry costs nil or at least minimal. For full
licensing details see the Licensing
So if everything
is free how to I make any money as a developer?
The software, documentation and hardware designs are available under
the Creative Commons license and are therefore freely available to
you and everyone else. But not so any code you write or physical product
you design or build from the specs.
But what does it do?
All this tech talk is nice, but what does BUSnet actually do?
In non-techo language BUSnet (with a suitable application such as
MAXX) can reduce
or even replace the rat's nest of wiring common in RVs, especially
old ones. It will allow you to monitor all kinds of things such as
your batteries and fridge.
BUSnet is not just for those big flash motorhomes, a simple system
is equally useful in a small camper, 4x4 or a caravan, after all they
have fridges and batteries as well.
Some examples are.
- Battery monitor — a BUSnet
system can monitor all aspects of your battery usage, from immediate
current and voltage to averages, minimums, maximums, individual
batteries in a bank, low voltage alarms, state of charge etc.
- Fridges — a BUSnet system
can monitor just about everything a fridge does including but not
limited to, door open (with alarm if driving), temperatures, compressor
duty cycle, current used, voltage at compressor and of course min/max
temps. Even data logging of all the above displayed in graphical
format on your laptop is possible.
- Water — automatically
isolate pumps while driving so a burst hose doesn't pump the tanks
dry. Stop pumps from operating at 2AM when the water pressure drops
because of the temperature.
- Solar — Shows how many
amps being produced, amp hours for the day etc.
- Cab gauges — with BUSnet
you can replace old faulty non-linear gauges with a "glass
dash" and while you're at it get a digital speedo and ten trip
meters to keep track of distances since last oil change etc.
- Bin doors — would you
like to know that all the bin doors are closed before you drive
off, or that one has sprung open while driving, or maybe that someone
is opening one in the middle of the night? BUSnet can tell you this.
All this information can be displayed on a single display, or on
as many displays as you like. There's no reason why a control unit
cannot be placed in a car to keep track of the systems in a caravan
while driving for example.
BUSnet and MAXX are also targeted at commercial and light-industrial
applications such as aquariums, control panel retro fitting etc.