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Discussion Starter · #1 ·
This project is a fully designed bespoke digital boost gauge for use in high pressure turbocharged applications.

There are gauges out there with 1 Bar maximum range and 10 LEDs, but these lack resolution and cannot cope with the pressure requirements of a chipped petrol engine or a high performance diesel.

My car produces typically a peak pressure of 1.4 Bar G at the intake manifold.

My design will incorporate a Motorola MPX4250ap pressure transducer (capable of 0.2 Bar to 2.5 Bar absolute or -0.8 Bar to 1.5 Bar gauge)

The sensor is specially imported from the USA, as UK based supplies are apparently nonexistent.

At the heart of the design is the pressure sensor, supplied with a regulated 5V source.

The processing of the signal is simple and the representation will take the form of a 20-LED bargraph.

The old-skool favourite LM3914 IC holds the key to the LED driver system.

Two chips in cascade arrangement, allowing zero at the first LED and perhaps 1.4 Bar (settable) at the farthest end.

Here's where it all starts......the prototype.

Not much to look at but it's working 100% correctly on the breadboard.

Posted Image


The led bargraph displays are just for test purposes (i have 20x of these so just holler if you want one for £1 each!)

I am now designing the PCB, which will carry all the main components.

Not sure about where to locate the pressure sensor......it's possible to place under the bonnet in an IP rated box perhaps.

Am now also working on the LED arrangement - I have white and blue 3mm leds arriving from Hong Kong next week, so you can already get a flavour for the theme!?
 

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Foxy does it again [:D]

I'm especially looking foward to this mod Jon, i've been toying with the idea of a boost gauge for a while now, but really dont like the round tacho (?) gauge design.

Any idea's on sizing and possible positioning of the unit yet?
 

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Discussion Starter · #3 ·
Tabs

Glad you like the idea.

I'm just adjusting my thoughts on the pressure range.

Perhaps need to include a negative pressure with respect to atmospheric, in order to truly represent the required range.

The engine will produce a fair negaive pressure (suck) when there's no boost, and also when closing the throttle under boost.

Here's a simple idea.

Using 3mm LEDs, the LED centreline is just 30mm diameter.

Posted Image


There are, of course, other choices and the linear arrangement has certain advantages.
 

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I thought you don't get negative boost pressure on the Golf TDi's as they are drive by wire and hence have no throttle plate. I looked in to this a while ago, even got the leds and sensor but never completed it, during the time I was looking around for gauges etc everyone that I spoke to came back to me with a gauge that only showed positive pressure.

Vwdubster77
 

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Discussion Starter · #5 ·
Thanks for the info dubster.

I would appreciate any further info on this if you have it m8.

The adjustments can be made at build stage, to give whatever range is required, with or without vacuum.

Why didn't you finish off the project?
 

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Foxy..

how would you go about calibraiting something like this?

Personaly.. I would love a bar graph version.. so i can install it verticaly in the a-pillar. Can you get the same colour ranges in a bar graph?

Amit
 

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How about this for a possible position definitely different, but where would you then locate the lighting switch?

Posted Image
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- Hope this is of help.
 

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Discussion Starter · #9 ·
Cappy

For ease, the gauge would have to be calibrated using a voltage source and a DVM.

The transfer function of the pressure sensor is known, so the rest is easy.

(at Atmospheric the sensor outputs 1.75V and at 1.5Bar gauge, it outputs 4.75V)

The LED arrangement is easily rearranged, so all you need is a vivid imagination!

As to the bargraph style LED stacks - I bought 20x red recently as a job-lot for a good deal, just for messing bout with.

Have seen multi-coloured but extensively in the USA market.

They get used for air/fuel meters..........another simple project - you just use the signal from your lambda sensor and away you go.

There are several simple 10-led designs for this a/f meter on the web.

GTi Jazz

With 20 leds, it hink we may struggle in getting them into the switch cap, but i haven't given up yet!

The area above the steering column sounds good, but for some drivers who like the steering wheel set high, it may be a problem.

I had a look today for alternatives, and there is an area to the bottom right and bottom left of the clocks (instruments) which would accept a slim, small pod with 20 leds mounted on it.

Sputnik

Would you adam & eve it!

I was thinking along similar lines at the weekend!!!

An array of leds arranged AROUND the switch........technically i think it would be impractical tho!

Keep up the good work guys - i need your ideas....
 

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Discussion Starter · #11 ·
Yes, Dubster, that's an article i had already read and used a couple of the ideas.

That design uses the same sensor as mine, but has just 10 leds.

No criticism, that guy put alot of work into getting that one produced.

His pcb and schematic are inaccessible to me as i don't have the Eagle software.

I wanted to do my design from scratch and have happily achieved it already.

Anyways, here are some more images of ideas for you to guys to 'chew on'.....

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some possible ideas for locations (3x here by the way!!)

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3mm leds versus bargraph led stacks.
 

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I like the one up the side of the instrument binnacle the most, also like the one in the switch. The bargraph stack LED's look like they belong in KITT from Knight Rider - cool!! [:p]
 

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foxy.. can you get the bar graph stack in the same colours as they regular LED bar?

The LED bar is a little long for my a-pillar mounting plan.

Amit
 

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very nice but is the one which goes up with the revs the boost one which you are trying to make or is it the one underneath which is above the clock?
 

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Discussion Starter · #16 ·
The one which appears to rise with the revs is the boost level

The one below is air/fluel ratio (petrol engines), which is a breeze of a mod and runs off the lambda probe in your exhaust system.

0-1v output.

Not much use IMHO unless you want to fine tune your fuel or air system
 

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Discussion Starter · #19 ·
Cheers for the leads Johnny

The problem with a digital numeric readout is that it's basically great for static pressures but you start to use it for dynamic stuff and it'll just be a blur - looking like 8's all the while.

Damping the reading will just give you latency which is OK if you like 'driving thru the rearview mirror'

Personally, i think the analogue-esque bar display does the job well and you can even see it thru your peripheral vision, so ne need to even glance away from the road.
 

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what about the "dead" area above the computer in the dash, It could be put to good use and its in the drivers live of vision too.
 
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