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Did you know that the average car today has several kilometers of wires inside it? This figure is astounding and therefore car manufacturers have been looking for ways to reduce it. With the emerging technology of today's vehicles there are more and more devices with a need to communicate with each other and to share their data. As a result, in 1980s the company Bosch invented the serial bus where data can be sent with up to 1Mbit/second via a single twisted pair wire. This reduced the amount of wiring by a lot (and still there are kilometers of wires). Still, we can easily say that without it, today's cars would not be the same. |
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The CAN bus is not only related to cars. They appear in other forms of transportation like trucks, rail cars, tanks, tractors and other vehicles as well as for common measurements. There are lots of sensors readily available with CAN bus technology. They are very robust, fault tolerant and have a nice collision detection algorithm.
So, now we know what the CAN bus is. What do we need to measure the CAN bus? First, we need some hardware supported by DEWESoft.
Required hardware |
Orion, NI, Softing or Vector CAN |
Required software |
LT or higher + CAN option or EE |
Setup sample rate |
At least 1 kHz |
Then, if we measure in a car, we need to know where to connect this in the car. For "official users", this task is trivial since the wiring is known. We need be careful that the not-terminated wires are not too long since the vehicle bus can be interrupted with the connecting of the measurement instrument. If we have a sensor, or an array of sensors, there are connectors with labeled wiring. In this case, we need to make a bus, which is not that hard as it sounds, since it is only a twisted wire with 120 Ohms resistors at both ends and virtually any number of connections in between.
Only by correctly connecting to the bus can we scan all the messages sent through the CAN bus, but we will only see a message ID and raw data.
The third thing is that we have to know how to decode the messages from the CAN. For this we either need a description or a library. These libraries are defined by a Vector and are called DBC files. It has a full description of the messages with output channels. These libraries are a well hidden secret among car manufacturers and are propriety. For trucks, the messages are standardized and described in the J1939 standard.
