CANTEE question

[BenAmr2turbo]

Hello, I have a query regarding the CAN bus on my G4x.

I'm aware 200mm is the maximum cable legnth for adding an additional device, however;

From the canlambda controller I am adding to the CANTEE plug, is approx 200mm - BUT - there is around 100mm of loom on the CANTEE side also.

Do I need to modify the canlambda loom legnth with a new DTM plug to get the overall legnth below 200mm?

It seems a shame to cut up such a well made loom.

Is it that important/necessary?

What happens if the loom is over 200mm?

Also I am under the impression the added devices on a can bus dont need a twist?

Please correct me if I'm wrong...

 

Thanks,

Ben.

[koracing]

General practice I would make sure you have a 1" twist for all bus wiring.  I've made can-gauge looms 12 feet long for MR2s as the ecu is in the trunk and not had any issues running to AIM dash, MoTeC dash, or Link CAN gauge.  I don't think 200mm - 300mm is going to be any issue.

[Adamw]

It will be fine, the CANTEE is designed for exactly what you are doing.  

You are correct in that the main trunk should be twisted pair, but the stubs dont need to be.  The "maximum stub length" of 200mm which is in some of our documentation, im not sure where that originally came from but I've seen a few variations of that "rule".  For example the common CAN standard ISO11898 quotes 0.3M max stub for a 1Mbit bus.  Some standards instead use a calculation based on propagation delay and when you work through the calculation they often end up giving max stub length results of >1.5M for a 1Mbit bus, so I suspect in many cases it is not all that critical.  The reason for the stub length restriction is stubs are not terminated so you can get signal reflections that will bounce the voltage above/below the thresholds causing "bits" to be seen that arent actually there.  However, CAN has a very robust error checking and validation routine so these errors will not make any difference to the received data - just some devices will report the error on the bus so all devices will reject the message with the error and make the sender resend it.  I quite often end up with stubs longer than 500mm for things like curly cords to steering wheel controls etc and have never yet seen any obvious negative effect.

[BenAmr2turbo]

Great, I will give it a go and see what happens. Thanks for the info, it helps alot!

Two more questions I have about the MXG/Aim dash, then I think it's actually ready for mapping.

 

-1- Would I need a pull-up resistor in the ''fuel gauge'' wire to get fuel level to dash via analogue input? Or is the original input OK?
-I have it labelled as Pin 1 (grey Plug) from the original dash loom - but after some research I am not sure if it can be wired directly in..

-Being a '92 Mr2, I'm guessing the level isn't read by the ECU itself and doesn't show via the CAN line input either. (I assume the speed and RPM do)

-This is the best info I could find but I will need to manually verify the plug type/wire colours myself first.

https://docs.google.com/spreadsheets/d/1ZAP6F38OdxmFOPnNoAfrJ6Y5fGZUdG1HrXXHjVjAfko/edit#gid=0

https://www.aim-sportline.com/download/faqs/eng/hardware/sensors/FAQ_Sensors_Fuel_level_100_eng.pdf

One advantage I have is the tank is empty, so I have at least one known point, but it is installed so can't access the sender anymore.

 

-2- Can the other original dash inputs wires; like indicators etc. be wired directly to Analogue 1-8? and do they need a ground?

-There is only one ground listed in the original loom (except the speedo ground) I think i need to attach indicator and light tell tale wires to analogue input 1-8 on the spare plug, but do they need the ground from the original loom?

-Once I have ignition on - I will test the original loom voltage outputs - but just need some general info about what the dash will expect to see.

 

Many thanks for all the help and replies!

Ben.

[koracing]

Yes you will absolutely need to add a pullup resistor to the level sensor input.  I made up a worksheet to figure out votage ranges once for doing just this on an MR2 with a AIM MXG dash I was working on - a good resistor value is 237Ω (or two 120Ω resistors in series).  Maximum current is .02amps or less and voltage range is approximately 60mv to 1590mv using 5v reference.

[Adamw]

This doc here gives some general info about connecting and setting up the basic lamp signals:  https://www.aim-sportline.com/download/faqs/eng/hardware/sensors/mx_series/FAQ_Sensors_MXx12_StradaSpieIcone_100_eng.pdf

The lamp signals connected to dash inputs dont need a dedicated ground, they will work via chassis ground.  Fuel level sensor would benefit from a dedicated ground connected to the dash analog ground provided the sensor does actually have a ground wire - many dont.    

[koracing]

The three wires on an MR2 SW20 level sensor are Ground, Level output variable resistance to ground, and low level sensor sensor lamp/switch to ground.

[BenAmr2turbo]

That's great, Thank you!

So I have 240ohm resistor for the gauge..I have no way of moving the float - until I fill the tank - so i'll have to calibrate it afterwards and check the input is right I guess. - I may leave the pin disconnected for now and set it up once I know the full tank resistance output..

Does anyone know if the low fuel lamp needs a 40-80ohm resistor as stated in the above aim document?

 

The rest seems simple enough now I have the original cluster pinout worked out..

Thanks again for the help,

Ben.

[koracing]

If you have the fuel level sensor working, it's easy to set up a low level warning in the AIM dash, so I've not typically bothered with the low level light thing on the OEM level sensor.

[BenAmr2turbo]

I have both the MXG and CANLambda connected via the cantee to the ECU.

The dash works OK and is transmitting some data.

My question is..

Would I select "Can 1" for the Wideband Lambda on the top left of the can setup screen? Have them both with the same "CAN ID 1000"   "User defined mode"  "1 mb/s" - But, on separate channels in the bottom left box? Or do they need different ID?

Thanks, 

Ben.

[Adamw]

If you hit the help button at the bottom of the CAN setup screen it will take you to the CAN section of the help file, click on the "Device Specific CAN Information" page and you will find set up instructions for both.  The Lambda should be on ID 950.

[BenAmr2turbo]

Excellent! I got it, Thanks!

[BenAmr2turbo]

So my "fuel gauge" wire is connected to my dash - "analogue input 1"

I may have made a mistake by not connecting "ground" to the dash - analogue input 2, is this completely necessary? I have an indicator on input 2.

 

 

I have the 5v reference voltage connected to that wire - via a 240ohm resistor, wired as it should be.

I have seached forums and found the resistance values are usually 3ohms with a full tank and 110ohms with an empty tank.

What can I do to check this is right and setup the level sensor?

 

I'm guessing I can check the output as I fill the tank but struggling to find that in RS3 if anyone has any tips?

Thanks for the info on the other things - the indicators and all the other warning lights are working and the dash works great, I like how you can set the parameters for each light.

 

Thanks,

Ben.

[BenAmr2turbo]

Okay, I found the "live measures" and did some digging, found 1950mV coming from channel 1!

 

So I've setup a percentage gauge from 1950mV empty - to 0mV Full - for now, which seems to be working well using no decimal places and it's showing 0%

One last thing for the dash.....

The MAP reading on the dash is 14psi.

How do I get it to showptheamount of pressure above the barometric pressure for a boost gauge?

 

Thanks,

Ben.

 

EDIT: I'm just having a moment - When the engine starts it obviously will read a vacuum! I just thought it would say zero for some reason xD ??

 

 

[Laminar]

MAP is absolute so it will always read positive. If you want to see negative for vacuum and positive for boost, use the parameter MGP.