At its most simple, communication is getting information from one place to another. As we saw in the article ‘why use a communication bus’ we look at a bus to simplify the control of devices with fewer wires. Ultimately we will send instructions from one device (headlight switch) to another headlight, in a digital form. Let’s see how CANBus communication might help transfer messages.
CANBus
CANBus is currently the most broadly used vehicle communication method in automotive applications. To simplify the concept, we can break the compound word down to try to determine its purpose.
The CAN element of the word stands for “Controller Area Network” and refers to a method of sending information from one device to another anywhere within the vehicle.
The ‘bus’ is the physical media (twisted copper wires) to which all electronic devices are connected. There is often more than one single set of wires (multibus).
CANbus is one of a number of communication buses used on modern vehicles. Other examples include LINBus, FlexRay and Ethernet. While the busses can be physically different (one, two or more wires), the primary differences in the communication types relate to the amount of volume of messages and the cost of electrical hardware.
One to one Vs one to many
For us humans, communication between two people using the telephone network usually goes along the line of;
- Pick up the phone handset,
- Dialling the other person’s number,
- The switchboard connects the right wires,
- Finally, you speak to the person at the other end.
CANBus is nothing like this. There is no switchboard or master controller, for a start, and there is no privacy! It’s like a thousand voices screaming out, at the same time.
Benefits and Limitations of CANBus communication
The CANBus method of sending signals, like any communication method, has positives and negatives. It’s possibly the best automotive comms bus for cost per signal, with speeds up to 1Mbps. It’s also got an excellent transmission distance of 100m. This might seem extreme in a 5-metre long car, but loops back and forth soon add up. But it’s a unidirectional comms bus meaning only one node can talk at a time.
Who shouts the loudest on the bus?
Photo by Rob Curran on Unsplash
CANbus is closer to having an entire company worth of staff locked room and they communicate by shouting. Every member of the staff hears the person shouting the loudest at the same time. Fortunately, this is a company with a classical management structure and so there is a hierarchy, and engineers will be quiet and listen to their manager, the managers will be quiet when a director is speaking.
So CANbus isn’t the sort of communication people would use, but for computers, it works very well and boy do modern cars have a lot of computers!
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