Help making virtual car - diagnostics on the bench !

[rugged]

Hello,

I am trying to construct a "Virtual Car".

This means having a range of ecus on the bench, connected up via K or L lines / Canbus, then powered up with 12v power supply. The idea is to then connect a diagnostic link cable ending in a female OBD2 16-pin socket.

Now it should be possible to connect a standard Inpa / GT1 / VAG cable and at the very least be able to connect and Identify the controllers from within the diagnostic software - Inpa is very good at this. My problem is that I really do not know how to wire up these ecus - should they be in parallel or in series. Also, it has proven very difficult getting the pin-outs to these different ecus, so any help is grafefully accepted.

My aim with this project is to use the ecus to test if the cables are working or faulty. I am presuming that if the cables can connect to the ecu and identify it, i.e., Coding Number, Hardware/Software Numbers, Date of Manufacture etc etc, then it can be assummed that the cable is 'fine'. At this time, I do not intend to connect any sensors to any of the ecus, but will play around with that later.

Right now, I have two sets of ecus, one for the E39 Series and another for the E90 Series.

This is what I have:-

E39.
Engine Ecu Siemens DME MS43
Gearbox Ecu Bosch GS8.32
Airbag ECU Temic R6T6M17A0N1
ABS Ecu Bosch 0265109023 / 65. 77-8374799

E90.
Engine Ecu Siemens VDO DME MSD80
ABS Ecu / Pump Unit ATE 3452 6776056 - 01
Airbag Ecu Bosch 0285 010060

So, is it possible to connect ALL the above ecus together, or do I have to seperate the E39 from the E90 ? I presume the E39 is K + Can, and the E90 is DCan. I will be very grateful for any help in this project.

Thank you

[AaronM81]

ECUs traditionally are used at the beginning and/or end of the data bus. This usually done because each bus (pair of wires) needs to have a certain resistance across it and ECUs are a great place to house resistors. When you dont have an ECU (or have one with a resistor in it) at the other end of the bus, you need to terminate both wires with a single resistor. For CANbus, the resistor value is 120ohms...not sure about other systems.


So, to recap...A dabus looks like this (dashed lines represent Hi/Lo wires of bus)


ECU=====================ECU (or terminating resistor)


The wiring of the databus is critical. (i dont know how to upload pictures or i'd show you an example) - Basically each device that is connected to a data bus is called a "drop". Each drop cannot be more than 300mm long and spacing between drops should ideally be no closer than 100mm (dont quote me on the exact values, been a while since i designed a CANbus network). Exceeding these values will potentially cause bus load errors.


Creating drops (attaching devices to the network) is done by splicing in both HI/LO can wires to the main bus. You should never have more than three wires in a CANbus splice. ( Splice 1: Main HI bus IN + Drop HI + Main HI bus OUT Splice 2: Main Lo bus IN + Drop Lo + Main LO bus OUT).


REMEMBER: you cannot make a drop off of a drop. Data buses do not operate the same as power/ground circuits. Each drop has to come from the main bus wires.

Data bus wires are usually twisted pairs 18/20 AWG...the twisting doesnt have to be very tight, one twist per inch is probably sufficient.


Since you are playing around with vehicle electronics, you will most likely have numerous buses on the system. Each bus must remain seperate. However, each ECU could terminate numerous buses, just depends on the system.


FYI - the company i work for builds virtual machines, a.k.a. Hardware in the Loop (HIL) cabinets, for some of its customers. It takes a whole lot more than just hooking up ECUs... Even if you establish databus connections, you will be faced with an unlimited number of fault codes related to the lack of sensors/actuators/etc. Even powering the ECUs properly can be tricky...any main controller would likely need to see a key switch signal that pulls a main relay coil to ground thus allowing the other power inputs (each individually fused) go live. A simple mistake such as bypassing and just hotwiring the power can cause ECU after run faults (the ecu remains active for 90 sec or so after keying off to log fault codes, data, etc).


Bottom line, im not sure what you are hoping to accomplish by doing this but to make it anything remotley diagnostic will literally cost you $50K plus in signal generators(you gotta fake in environemental variables & other signals that you cant get because you dont have an actual car)/instrumentation/devices/etc


Best of luck!

[RobertFontaine]

Take a look at the "Megasquirt stimulator"

[AaronM81]

Checked out the Megasquirt, looks like a neat device! Have some thoughts/questions tho...If you've had experience with this thing and can set me straight, please do.

This stimulator was made to work with the Mega Squirt ECU...not saying it cant be used to simulate inputs to other ECUs (if you know the pinouts and signal requirements) but at best it sends analog input signals and very basic ones at that.

Also, outside of the EFI system, what other diagnostics can this allow you to perform?