Must shielded cable be used

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Must shielded cable be used

Postby kojab » Wed Apr 16, 2014 6:45 am

Is it necessary to run grounded shielded cables between a VR distributor (Toyota 3SGTE) and your Dual VR 2.1 board or can the factory four wire non shielded cables be used. It is understood that only two VR signals will be used from this distributor.
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Re: Must shielded cable be used

Postby jbelanger » Wed Apr 16, 2014 12:00 pm

The board will detect very small signals so it is recommended to run shielded wires. However, you could give the OEM cable a try and see if that works. But you are likely to get noise on the signal.

Jean
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Re: Must shielded cable be used

Postby kojab » Tue Aug 26, 2014 2:36 am

Hi Jean.

Have been trying now for a few months to get this dual PCB to run with a Toyota 3SGTE distributor. I have read all threads on this forum and tried all combination used by other forum members. But still no luck.
Problem seems to be, I get it to work perfectly at some rpm ranges and not at others The NE signal is always stable but G2’s content is heavily mixed with the NE signal and the 2.5 volt threshold is being falsely triggered by the unwanted NE signal.

I understand that these boards are set up for A2 mode and wonder if its possible to modify this dual board for A1 mode so the bias threshold can be adjusted to only trigger on the G2 signal.

Current configuration is;

Using 1k ohm across NE VR sensor then 33k to VR1+

500 ohm across G2 VR sensor then 33k to VR2+

- G common to NE & G2 VR sensors and is also connected to VR1- and VR2- via two of the 33k resistors mentioned below.

4 X 33 K ohm resistors used in series as input to dual board ( VR1- , VR1+ ,VR2+ , VR2-)

Appreciate any help you can give.

Richard
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Re: Must shielded cable be used

Postby jbelanger » Tue Aug 26, 2014 10:15 am

Richard,

To modify the board to run the A1 mode would require lifting some pins and reconnecting them to other places and you would also need to add the needed components. I don't think it is doable without destroying the board not to mention that doing that on such a small package and small pitch would require some very skilled with good equipment; I would never attempt this.

So short answer: no.

As for the rest, have you tried no resistor on VR-? Using larges ones, or any at all, does not seem like a good idea.

But if the signal is a slow one with more than 85ms between pulses, it is going to be very difficult to get it working if there is noise on the signal. That's the timeout for the adaptive peak threshold mechanism inside the chip and after that it will get triggered by a very small peak.

Jean
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Re: Must shielded cable be used

Postby kojab » Thu Sep 04, 2014 7:38 pm

Hi Jean.

I have tried again with no resistor on VR- on my test bench where there is no noise on the signal and it is still false triggering . In saying that it really is doing what it’s designed to do, lock on to a signal at the threshold voltage. The problem is obvious, at low cranking speed the 85ms applies which will favour the NE signal not the G2 signal which is want we want to use for our trigger. I had thoughts about designing a RC filter to reduce the amplitude of the NE signal but knowing how sensitive the MAX9926 is, it’s very unlikely to work.

My own initial thoughts were that this dual board would solve the problems over a LM324 design which ran the engine but had misfires at higher revs. Unfortunately I have not been able to even start the engine let alone run it with the dual board.
From reading here it seems others have managed to get it to work but I want something that will work perfectly (straight off, stable) and not be a fudge. It is in my opinion the dual board is not suitable in its present form for the standard 3SGTE distributor unless possibly the internal earths are separated within the distributor which is not what I wanted to do.

I am embarrassed to say I have spent many weeks trying to get this to work to no avail. My oscilloscope clearly displays where the problem is.

Jean I appreciated your help.
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