Dash2 setup and CAN

stevieturbo
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Joined: Sat Jul 05, 2008 3:54 pm
Location: Northern Ireland

Postby stevieturbo » Thu Aug 06, 2009 2:21 pm

Sorry, should have been more specific.

open circuit, infinite resistance.

Originally measured at my ecu plug, unplugged.

Then when I got no reading, I tried at the RS232 labelled plug off the CAN adaptor probing the pins directly, incase there was a problem with my short wiring to my ecu.

Again, open circuit ( hence I opened it up to confrim the wires are still soldered to the pins, which they appear to be )

I then tried with 12v power applied ( ie, ign on ) still the same.

stevieturbo
Posts: 55
Joined: Sat Jul 05, 2008 3:54 pm
Location: Northern Ireland

Postby stevieturbo » Mon Aug 10, 2009 8:50 am

bump.


Would this lack of any resistance reading perhaps indicate a faulty unit of some kind ?

Might also explain why I cant get any sensible info on Lite Monitor and the Dash2 ??

stevieturbo
Posts: 55
Joined: Sat Jul 05, 2008 3:54 pm
Location: Northern Ireland

Postby stevieturbo » Thu Aug 20, 2009 6:38 pm

It's like getting blood from a stone here :?:

Support

Postby Support » Wed Aug 26, 2009 12:56 pm

Could you please send an email to Martin (mhill(at)race-technology.com) he will assist you with the problem.

stevieturbo
Posts: 55
Joined: Sat Jul 05, 2008 3:54 pm
Location: Northern Ireland

Postby stevieturbo » Wed Aug 26, 2009 6:16 pm

Support wrote:Could you please send an email to Martin (mhill(at)race-technology.com) he will assist you with the problem.


I did over a week ago, although didnt follow up on it.

Will do again.

stevieturbo
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Location: Northern Ireland

Postby stevieturbo » Thu Aug 27, 2009 6:54 pm

email sent 26/08/09 evening....

GMS Racing
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Postby GMS Racing » Mon Sep 21, 2009 9:13 am

I attach a pic of what the circuit should look like. There has to be some resistance in the circuit.

Image

Generally, the ECU will be terminated with 120 Ohm and the last device on the bus should also terminate with a 120 Ohm resistor. So worst case is that you must measure 120 Ohm. Exactly where are you measuring?
Regards,

Gary...
Johannesburg
South Africa

stevieturbo
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Location: Northern Ireland

Postby stevieturbo » Mon Sep 21, 2009 9:47 am

I think my original readings were off somehow.


Last time, I did indeed read 120 ohms with everything connected up, measured on the 2 wires just before they enter my S80Pro.

I added a 120ohm resistor across this in parallel, which then brought that reading to 60ohms.

However. Channels display slow on both Dash and Lite monitor. Voltage and MAP still do not display properly, and on Lite Monitor, channels still apopear and dissappear at random.

I did make a few logs on Lite Monitor, but as yet have done nothing more. TBH, Im pissed off with and really cant be bothered. If I had thought for a second it woiuld be this much hassle, I'd never have bought it.

By MCU I assume you mean the DTA ?

What to you mean by Transceiver ? and Nodes ?

I simply have my DTA ecu, the CAN adaptor and the Dash2 ( or Lite monitor ) attached

GMS Racing
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Postby GMS Racing » Mon Sep 21, 2009 10:56 am

Sorry, I think the diagram is confusing you. This is merely a representation of a "typical" CAN bus connection in a normal road car. The point I was trying to show is that it must have 120 Ohm at both ends.

If you are now measuring 60 Ohm then the circuit connections should be correct.

Regarding the speed of data display I cannot help you there as I do not have this setup. One thing to check is the earthing of all the relevant components. If possible, run a direct earth between the S80 and the Dash 2.
Regards,

Gary...
Johannesburg
South Africa

stevieturbo
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Joined: Sat Jul 05, 2008 3:54 pm
Location: Northern Ireland

Postby stevieturbo » Mon Sep 21, 2009 5:25 pm

My DTA and Dash2 both ground to the same point on the chassis. Done deliberately to minimise any voltage offsets for the Analogue channels in use.

Update varies, but is typically less than 1Hz on Lite Monitor.

It really makes no sense. Even something as simple as TPS, engine off, is very slow to register gioiung WOT and closed again.

Peter Carroll/Toronto
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Postby Peter Carroll/Toronto » Sun Jul 25, 2010 3:08 am

I wonder if this explains why I am having so much trouble with the can adapter.

CAN is a bus (like SCSI) and each end of the bus must have a termination resistor to absorb the signal and keep it from reflecting back and forth (lots of noise) on the bus. Since my connection from the DTA was only a few inches, I thought I would skip the terminators. Maybe that was a mistake...

According to the CAN spec, each end of the bus should have a 120ohm resistor between CanH and CanL. So measuring them in parallel would be 60ohms.

Maybe all that noise is making it hard for the ECU adapter capture the messages from the DTA. This could explain why my readings are so sporadic.

I will test and let you know...
Peter Carroll, Toronto, Canada
DL1 and Dash2 - http://DriversMeeting.com/pcarroll

GMS Racing
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Postby GMS Racing » Mon Jul 26, 2010 8:25 am

Peter,

Having no termination resistors will not really be a big factor in noise (i.e. interference). If you have interference then you should use a screened cable earthed only at one end (to avoid ground loops). The 120 ohm resistor is actually to allow matching of the impedance. a matched impedance will maximise the voltage and give a stronger signal.
Regards,

Gary...
Johannesburg
South Africa

Peter Carroll/Toronto
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Postby Peter Carroll/Toronto » Tue Jul 27, 2010 10:05 pm

It can actually.

Having a high speed signal travelling down an unterminated data bus, the signal will bounce off the end of the cable and reflect back and forth on the bus. This is the same effect as a wave in a swimming pool reflecting off the wall of the pool.

In the computer world, a SCSI cable needs to have a terminator at each end of the bus for the save reason. If you don't have it, you will get unpredictable results. The CAN world is similar. Having the 120ohm resistor at each end of the CAN bus attenuates the wave and prevents if from reflecting back and interfering with the signals.

Since my CAN bus was only a two feet long, I took the shortcut of not installing the resistor. I thought I could get away with it. But it's probably a better idea to just wire it according to the CAN spec.

Also, I used a tightly twisted pair instead of a shielded pair. The theory there is that any magnetic interference would appear to come from all directions simultaneously and thus cancel out. I actually used a segment of CAN bus cabling from a new BMW. So I am not concerned about the cabling.

It also appears the DTA S100 ECU has the 120ohm termination built in. So I was just missing it at the RT end.

If you got away without one, maybe that just shows how close I was to getting away with it. Anyway, I have eliminated one more variable from my troubleshooting.

Thanks
Peter Carroll, Toronto, Canada
DL1 and Dash2 - http://DriversMeeting.com/pcarroll


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