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Practical Wiring - Club Level: Network Communication Design

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Network Communication Design

03.17

00:00 - In recent years it has become common place for performance automotive EFI systems to include network communications, particularly CAN bus network communications in their design.
00:09 Network communications can be a great thing as they allow us to send information from one part of the vehicle to another without each different piece of data requiring its own wire.
00:20 This can reduce the size and complexity of our wiring harness substantially, while allowing us to make future changes to the data being transmitted around the vehicle without needing to make any physical changes to the wiring harness.
00:32 At the modified street car and club day track car level, the most common use of a CAN network is to transfer data from the ECU to a dash display or logger.
00:42 But it's always a good idea to place a couple of CAN network access points in the wiring harness design to make the addition of other electronics which communicate via a CAN network in the future much easier.
00:54 I will always include two spare connectors on the wiring harness design which have a power supply from our main relay, a power ground and CAN high and CAN low pins for each of the CAN channels that the ECU has.
01:07 I will put one of these in close proximity to where the ECU is mounted and another in the engine bay, usually on the firewall.
01:14 These spare plugs let us temporarily install an electronic module that communicates via CAN in the vehicle in the future and in the case of our example FD3S, this will most likely be an exhaust gas thermocouple interface, allowing us to keep an eye on the exhaust gas temperature in the manifold during the tuning process.
01:32 This is always important with a rotary engine being on the hotter end of the scale.
01:38 When wiring a CAN bus network we will use 22 AWG wire twisted into a pair.
01:44 There is very little current passed along the network wires, so the small wiring is a good choice and it does make the twisting process easier as well.
01:52 In the practical skills section of the course we will demonstrate the process we use to twist this wire tidily and evenly.
01:59 The reason we use twisted wire is that it ensures that any radiated noise which gets into one of the CAN wires will also get into the other.
02:07 The CAN protocol can handle noise that gets into both wires because there is what is known as a differential signal.
02:13 This means that within limits the absolute voltage level on the CAN wires when compared to our sensor ground level is not particularly important, it is the difference between the levels on the two CAN wires that the ECU actually looks at.
02:28 If an eight volt spike appears on both CAN lines, the difference between them will not actually change and the devices on the network will still be able to read the signal.
02:38 As outlined in the wiring fundamentals course, we need to cater for termination resistors in our CAN network design.
02:44 For our RX-7 example, this will be taken care of in the small sub harnesses that we will need to make to connect any devices to the auxiliary CAN access points on our harness.
02:56 We do it this way because it is possible the module we're adding might have an integrated termination resistor.