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Author: Subject: 5Vref for "6v-24" VDO pressure gauge?
ElmrPhD

posted on 22/5/17 at 03:59 PM Reply With Quote
5Vref for "6v-24" VDO pressure gauge?

Hi,
Trying to get my head around how I think others managed to do this: Use a VDO pressure gauge, which I believe are all rated "6V-24V" with a 5V reference voltage for the required pull-up circuit. Required, that is, for my Race-Technology Dash2, which requires changes in voltage rather than simply changes in resistance.
Westfield do this, I think, according to posts by the immortal "Frosty", but I'm not 100% sure.
Race-Tech tell me that it won't work, but then Summit Racing's tech guy says the VDO doesn't require any voltage to work as it merely provides resistance for a signal.
I'm so confused!

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femster87

posted on 22/5/17 at 04:19 PM Reply With Quote
there you go

http://westfield-world.com/rtdash2.html

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ElmrPhD

posted on 22/5/17 at 05:01 PM Reply With Quote
Thanks.
Indeed, that was precisely the article that I was referring to, and I've read it many times. But I see now that I wasn't clear.
What I need to know is if the VDO pressure sender they use is also stated as being "rated for 6V-24V" like mine is.
If I could confirm that, then I could assume that my VDO will also work with a mere 5Vref. And that would make me very happy as I've already installed it and the wiring is tucked away deeply in the loom/harness under the scuttle.
So...anybody know:
- which model of VDO pressure sender Westfield use, or
- if a pressure sender rated as 6v-24v will work with 5v
???

Thanks, anyway,
Steve

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lsdweb

posted on 22/5/17 at 06:58 PM Reply With Quote
A bit of help here - https://www.race-technology.com/wiki/index.php/HowDoI/Connect1Or2WireSensorToDL1

And some info on the forum from 2007 when I fitted a VDO sensor to my DL1 / Dash2

http://www.race-technology.com/forum/viewtopic.php?f=4&t=471

Wyn

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britishtrident

posted on 23/5/17 at 05:02 AM Reply With Quote
The easy way to get a 5v reference is device called a UBEC which is used by drone and model aircraft builders , very cheap clean stable 5 v output from any 9 to 28 volt DC supply.
Look on eBay or Amazon. I use one as supply for my in-cylinder pressure transducer.





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jeffw

posted on 23/5/17 at 05:47 AM Reply With Quote
The 5V reference in this instance is supplied by the Dash2. Remember you are connecting the sensor not the gauge to the Dash2 so the 6V-24V on the gauge doesn't matter. Follow the instructions on the pull up resistor size and how to connect it and it will be fine.






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peter030371

posted on 23/5/17 at 06:26 AM Reply With Quote
quote:
Originally posted by jeffw
The 5V reference in this instance is supplied by the Dash2. Remember you are connecting the sensor not the gauge to the Dash2 so the 6V-24V on the gauge doesn't matter. Follow the instructions on the pull up resistor size and how to connect it and it will be fine.


Like what he says above, I have just done the same thing with a sensor I got from Variohm and it seems to be working fine

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ElmrPhD

posted on 23/5/17 at 06:51 AM Reply With Quote
Thanks everybody!!!
I'm a happy man!

Jeffw, once again, answered my question, perfectly.

Britishtrident - that is exactly what I had already done as a consequence of an earlier question to this fantastic resource. The Dash2 has very limited 5v current supply capacity, but now I'm set with abundance. Like you said, they're dirt cheap!

And just so you know, all the links provided (thank you!) I had already memorized prior to having to ask my question.

Ok, I'm off to the garage!
Steve, in the NLs

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peter030371

posted on 23/5/17 at 08:34 AM Reply With Quote
quote:
Originally posted by ElmrPhD
The Dash2 has very limited 5v current supply capacity


The Dash2 is specified as 50mA (the Dash2Pro has 2 x 500mA which is a big improvement), with careful selection of pull-up resistor value it may be possible. What is the spec of the VDO sender? Do you have any other senders on the 5V reference?

If you can do it then getting the reference from the Dash is better as any slight variation in reference will also be 'matched' in the Dash itself that will give more accurate results i.e. a separate module might drop to 4.9V (as an example) under stress from heat etc and the Dash could go the opposite way.

However if you have to use a module its still heaps better than the old fashioned gauges running off 12V ± house brick (that's a technical term around here)

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ElmrPhD

posted on 23/5/17 at 09:07 AM Reply With Quote
Hi Peter,

Are you a Race-Technology supplier??? ;-)

The VDO pressure sender has merely 10 Ohms when engine off (184 Ohm at full chat). I have a 150 Ohm pull-up resistor in line with it.

In addition, from my 5V "box" I also have:
- a VDO dip-tube type fuel sender, again, only a few Ohms when "full", with a 150 Ohm pull-up resistor.
- the original Honda coolant temp. sensor - yet to be calibrated
- an oil temperature sender - yet to be purchased!

My Omex ecu is using its own 5V source for the TPS and an Omex-branded CTS.

I don't think I'm using the Dash2's 5v source for anything, but the Dash2 and my 5V "box" are grounded to the same point.

Would you mind elaborating on your last sentence about the problem of "old fashioned gauges running off 12V ± house brick"?

Thanks for the info'!!

Steve

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peter030371

posted on 23/5/17 at 09:33 AM Reply With Quote
quote:
Originally posted by ElmrPhD
Hi Peter,

Are you a Race-Technology supplier??? ;-)

The VDO pressure sender has merely 10 Ohms when engine off (184 Ohm at full chat). I have a 150 Ohm pull-up resistor in line with it.

In addition, from my 5V "box" I also have:
- a VDO dip-tube type fuel sender, again, only a few Ohms when "full", with a 150 Ohm pull-up resistor.
- the original Honda coolant temp. sensor - yet to be calibrated
- an oil temperature sender - yet to be purchased!

My Omex ecu is using its own 5V source for the TPS and an Omex-branded CTS.

I don't think I'm using the Dash2's 5v source for anything, but the Dash2 and my 5V "box" are grounded to the same point.

Would you mind elaborating on your last sentence about the problem of "old fashioned gauges running off 12V ± house brick"?

Thanks for the info'!!

Steve


lol, no but just been through all this myself on my build

With so much needing a 5V reference and the current sensor being so low value you are not going to be able to run them all off the Dash output

To be honest if you could just run one off that output it would be the Oil Pressure as that is the most important one though

'old fashioned gauges running off 12V ± house brick' The 12V on a car is very rarely 12V and goes up and down all the time depending on the electrical load on the system. At idle and under full electrical load at night my old fuel gauge would move ±5% in time with the indicators as the alternator struggled to keep up and the damping in the gauge tried to keep up! The Dash2 will able to filter things like this out though with the right settings


Have you thought about using the serial output of the ECU data to feed the CTS to the Dash rather than add another sensor?

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ElmrPhD

posted on 23/5/17 at 10:20 AM Reply With Quote
Hi Peter,

Yep - I bought the cheap 5Vregulated box as a means to stop worrying about frying the Dash2's limited 5V current capacity. One point of confusion largely squared away. This is important for me as I struggle to understand how to utilize this impressive, but confusing Dash2.

Agree about using the Dash2 to power the most important sensor (oil pressure), but in my previous request for help more than one guru/mentor/advisor suggested strongly that I not mix things up. I did not fully understand the issue, so I ran all I could off my abundant single source of 5V (the cheap 5V regulated "box", and grounded all I could to a single point.

Ah, of course! "12V" is never 12V, is it? Sad, cuz my (105 amp?) alternator is way overkill for such a simple kit car.

If I had to do it over again, I would indeed heed (JeffW's?) earlier advice to use the available ECU communication cable, but I had already wired things up "my way" when that advice came to me.

Now...are you going to be available to advise on the damping and filtering of the Dash2??? I only found some info' for the fuel sender, which was to set "Max rate of change" to 0.033 and the number of samples to 100. I have no idea if those are good values for my setup or even what they mean. Will have to look further into this subject...

Thanks again,
Steve

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