Bus voltage

[mini]

Follow on from a conversation with an auto tech,

On modern cars the bus communication voltage is generally 5V, this leads to all kind of problems vis a vis poor contacts/volt drop etc.

What is the nominal bus communication voltage on aircraft?

I'm assuming that a higher voltage increases reliability.

[ukv1145]

Hi Mini,

There are of course many standards of bus protocol used in avionics, manufacturers have variations on a theme and call them their own names for copyright reasons. One of the biggest standards is Arinc 429 which has a nominal 10V difference between the Hi and Lo lines. Also remember aircraft tend to use very high quality connectors that most of the time are not as exposed as the cheap ones under the bonnet of a car.

[purgatore75]

Hi there.....I try to add more of my previous collegue :)
An ARINC 429 data bus uses two signal wires to transmit 32 bit words.
Transmission of sequential words is separated by at least 4 bit times of
NULL (zero voltage). This eliminates the need for a separate clock signal
wire. That’s why this signal is known as a self-clocking signal.
The nominal transmission voltage is 10 ±1 volts between wires (differential), with either a positive or negative polarity.
Therefore, each signal leg ranges between +5V and -5V. If one leg is +5V, the other is -5V and vice versa. One wire is called the “A” (or “+” or “HI”) side and the other is the “B” (or “-” or “LO”) side.
This is known as bipolar return-to zero (BPRZ) modulation.
The composite signal state may be one of three levels:
- HI which should measure between 7.25 and 11 volts between the two
wires (A to B)
- NULL which should be between 0.5 and -0.5 (A to B).
This is an old but common standard in avionic comm, now is overcoming the Arinc629 with optic fiber so.......better tecnology surely but completely another story!
Bye bye....
- LO which should be between -7.25 and -11 volts (A to B)