Boost Gauge for VW Golf 3

Hello gentlemen,
I would like to install a boost gauge in my AFN Golf 3. Does anyone know a shop or online store where I can find these things cheaply? It's mostly for fun; those who know my history know that I actually don't need one anymore !
Or is someone selling theirs?

Hi.

... although the suction area only makes sense on the AFN engine to detect clogged intake passages/air filter, but otherwise, the device is quite usable - it's been running in my wife's Ibiza for over half a year *ggg*

I recently bought an LDA (Lambda Probe Adapter) from Conrad for about 40 EUR, but it doesn't come with anything else, so you'll have to buy the necessary T-piece and hose yourself. However, VW sells the original vacuum hose as a meter of material, and it's not even expensive.
But if you have a good tip on how to attach this thing to the A-pillar trim without too much hassle, that would definitely be worth thanking you for!
Bye, Matze.

Hi!
KW-Systems offers a bracket for VDO devices that can be mounted on the A-pillar.
Just send me an email.

Best regards.
Ventoman.

p.s.: Also also the Vento GLX with the 1Z engine as well.

))

Thanks for the replies. What pressure range does the LDA from Conrad cover? 0-1.5 bar? I just looked at KW-Systems, and while the A-pillar mount looks good, it's black (so it needs to be painted) and costs a quick 49?! They also have an LDA for 45? in their range. Hmm, I'm really considering it! It looks so funny!
@ Ulf: Are you selling those, or what?

Hello,

Unfortunately, I can only temporarily connect my pressure gauge to my A3 at the moment.
A small advertisement, for example, placed in a blank switch cover in the center console, would be great. Has anyone ever seen anything like that for sale, or knows of an advertisement that would fit?
I've been wanting to build a digital display using 3-7 segment displays and a voltmeter connected to the turbocharger pressure sensor... I have the parts lying around, but I haven't had the time yet. It's a lot of work. Connecting a hose is, of course, much faster.

Best regards, Rainer.

MarkusAFN wrote:

Thank you for the answers. What is the pressure range for the LDA at Conrad? Is it 0-1.5 bar? Bitte gib mir den deutschen Text, den du übersetzt haben möchtest. @ Ulf: did you get the ones I sent, or what?

No, it stays in the Ibiza. It took me quite a bit of work to shorten the connector at the back and convert the lighting from bulbs to LED (that beautiful Ibiza red with a hint of purple).

The Connrad LDA measures from -1 to ,5 bar.

@Rainer:

So, you wanted to directly use the boost pressure signal that the original sensor provides for this circuit, right?

Do you know how high or low of a voltage/current you can apply to this component without compromising the measurement? Because I see that as the main potential hazard.

Alternatively, if it's affordable, you could also install the exact same sensor again and only use that one - or were you planning to do exactly that?

Best regards,

Jan, who would much prefer an electrical cable to a pressure hose running across the car, and is still considering his options.

Hi Jan and Rainer,

Quote:

Do you know how high/low the voltage can be applied to this component without compromising the measurement?

Because I would consider that to be the main risk.

On the other hand, electronics offers proven solutions: an operational amplifier or emitter follower, powered by the (smoothed) supply voltage, can be used as a buffer or impedance converter between the sensor and the display.
The input impedance is in the megaohm range and should not significantly affect the sensor voltage.

Jan6K wrote:

@Rainer: So, you wanted to directly use the boost pressure signal that the original sensor provides for this circuit, right? Do you know how high or low of a voltage/current you can apply to this component without compromising the measurement? Because I see that as the main potential hazard. Alternatively, if it's affordable, you could also install the exact same sensor again and only use that one - or were you planning to do exactly that? Best regards, Jan, who would much prefer an electrical cable to a pressure hose running across the car, and is therefore still considering

Hello Jan, Unfortunately, I don't know the initial resistance of the sensor.
My approach was based on a voltmeter kit from Conrad; I need to review the circuit again, but the input resistance should not be a critical factor.
The circuit requires +5V, so I'll have to somehow solder a 7805 voltage regulator onto the board.
The calibration process also presents some challenges; it should display '0.00' at 1.8V and '1.50' at 4.65V.
The most challenging aspect is likely the "mechanically clean" integration of the three 7-segment displays into the switch blind cover.

Best regards, Rainer.

Hi Rainer,

Sounds good!

Of course, the question is how quickly a digital display can keep up, because especially during acceleration, there are short overshoots that could potentially be a problem. If the display really shows every change, it will jump quickly back and forth between the numbers.

I was thinking about combining this with an analog display, which would also make calibration quite simple. You could just create the appropriate scale while generating the pressure with a syringe or something similar, and then check the pressure with a conventional pressure gauge.

Of course, the question arises: how much does such a pressure sensor cost? Because I really don't want to tap into the one from the car. The issue of overloading could be solved, but as Ulf mentioned in the last discussion on the topic: Unlike a faulty pressure sensor, where the engine control unit is aiming for a specific pressure, you would see exactly that same pressure value with the same error (i.e., the expected pressure).

Best regards,

Jan.

Hello Jan,

"The circuit uses a clever IC where the sampling rate can be switched between 4 and 96 samples per second. Since it's also possible to read data using a diagnostic tool like VAG-COM at 3 samples per second, I don't think the fluctuating values will be such a big problem. Furthermore, the component also has a 'hold' function to 'freeze' the last measured value."
The input impedance of the IC is 100 MΩ . Therefore, a measurement circuit with minimal loading should be possible.
Unfortunately, the included 7-segment displays are green and too large, and they definitely don't match the other (red) displays in the car. That's why I got some smaller ones in red, so that the display fits into a free switch opening in the center console.
The part number for the panel meter at Conrad is 19 25 46.
I'll try to tackle the project this weekend. The panel meter is already soldered and tested; I still need to add the +5V power supply, design the appropriate input circuitry, and install the display in a switch housing.
I'm currently considering tapping the +5V directly from the power supply of the boost pressure sensor, let's see if it provides enough power .

Best regards, Rainer.

Hi Rainer,

Write about how it turns out; that sounds really interesting!

I would be cautious about using the 5V from the control unit, as those 7-segment displays require a significant amount of current, much more than the sensor itself consumes.

Furthermore, I suspect that the power levels within the control unit do not operate at 5V, but directly at 12V, which means the power supply may be inadequately designed.

I think I would use the 7805 for that.

Regarding the adjustment... maybe a few diodes to drop the voltage to 1.8V, and then a precise voltage divider for the rest.

Best regards,

Jan.

Jan6K wrote:

I would be cautious about using the 5V from the control unit (because that's ultimately where it comes from), because those 7-segment displays require quite a bit of current, much more than the sensor in question consumes.

Hello,

"That's a valid point! If the +5V power supply in the control unit fails, I'll have a problem... in that case, it's better to use the 2 additional components."

Best regards, Rainer.

Hello,

The circuit draws approximately 130mA, so I've added a 7805 voltage regulator and am sourcing power from the vehicle's comfort electronics system (e.g., infotainment, climate control). For safety, I've attached a small heatsink to it, as the power dissipation of about 1W noticeably heats up the voltage regulator.
I successfully neutralized the approximately 1.86V output of the boost pressure sensor at atmospheric pressure using 4 diodes (2x 1N4148 + 2x of an unknown type) from my parts bin, and then connected it to the panel meter using a voltage divider (10kΩ to 180kΩ).
The 190kΩ resistor and the diodes connected upstream do not represent a significant load on the output voltage of the boost pressure sensor.
It was quite a hassle to extend the 36 connection pins of the 7-segment displays using a flat ribbon cable and adapt them to a different pin arrangement (smaller, but super-bright, red 7-segment displays instead of the green ones that were suitable for the circuit).
The readability is excellent at 4 implementations per second and not too jittery.

Overall, the circuit actually works quite well, but there's a minor drawback that I only noticed later:
With weak/noisy radio stations above 102MHz, a slight humming sound is now audible. I might try adding a choke to the power supply line of the 7-segment displays, let's see where the broadband interference is coming from. I suspect it's caused by the steep voltage transitions when switching the individual segments of the displays.

Here are some pictures of how it looks when it's finished (I'll send you a better picture sometime, yesterday it was a little too dark for the camera).



Best regards, Rainer.

Hi Rainer,

Congratulations on this brilliant variation!

Do you also see the fluctuations in the engine speed when accelerating, which are clearly visible on the analog gauges?

Did you calculate the voltage divider based on intuition or calculation alone, or did you also compare it with VAG-COM for calibration purposes?

Best regards,

Jan.