Ladedruckanzeige Golf3 | Posts 16+

Hello Jan,

Yes, you can see the overshoots, of course not as well as with an analog device, but still quite well.
Regarding the voltage divider:
At a boost pressure of 1.5 bar, the panel meter input should read 150 mV.
The characteristic curve of the boost pressure sensor is known: 4.65V corresponds to 250kPa, and 0.4V corresponds to 20kPa. Between these values, the curve is linear (according to information from a source I trust).
That is, 4.65V - 1.86V (atmospheric pressure) = 2.79V, which is what remains after passing through the diodes. A variation of 0.2V up or down is not critical; this can be adjusted using the panel meter (which allows adjustment of the slope and zero point).
Therefore, 2.79V needs to be reduced to 150mV, which is a factor of approximately 19 (from 10kΩ to 180kΩ).
I calibrated it while it was disconnected by applying defined voltages. For example, +5V would correspond to approximately 1.70 bar (~170mV on the panel meter) with the sensor installed.
The current pressure readings on my pressure gauge correspond perfectly to those of the electronic display.

Best regards, Rainer.

Hi Rainer,

"That sounds really good! I'm seriously considering building one myself, because the design would be much easier to integrate into my Ibiza than any analog setup, which would require significantly more space for installation."

My only concern is that tapping into the sensor could create a problem from a warranty perspective, because how many average mechanics understand things like input impedance and the like?

Therefore, the idea is to install a second pressure sensor (somewhere within the pressure range) and use it. Does anyone happen to know how much this part costs at LLK?

My second thought (which I need to check in the Conrad catalog tonight) is to use a backlit LCD instead of LEDs. This would solve the color problem (Ibiza also has red), and it would also reduce power consumption.

Best regards,

Jan.

Hi,

As a "reference number" for a suitable pressure sensor for my Audi, I had the number 150 in mind, but I no longer remember whether it was in Euros or Marks. It was too expensive for me at the time to use the part as a blind plug for my coolant system.
Possibly, Conrad also offers a cheaper pressure sensor that you can attach directly to the circuit board, and then you would just need to connect a pressure hose to the internal chamber as usual.
Background: The former blind plug was fitted with a hose connection for a pressure gauge (for measuring boost pressure) some time ago. For durability reasons, I wanted to replace it with an original blind plug. However, I was unable to order it because the part number was missing.
However, the blind plug with hose connection holds better than I thought, and it has been leak-proof for months.

Best regards, Rainer.

I'll do some research to see what's possible... Sensors from Conrad are also quite expensive, in my opinion.

I think I might still have a blind plug lying around that I could use for experiments. I have my old, broken LLK (likely referring to a liquid cooling system) that I'm not using anymore, and something like that might be attached to it.

I would rather not have the hose running inside; instead, I would prefer to divide the system into two or three parts (pressure measurement, evaluation, and display).

But I'll tell you more about that later, when I have time; I'll browse the catalog later. The problem is that crafting here on the street is absolutely terrible; a solution that can almost entirely be created inside the apartment is the best .

Best regards,

Jan.

Hi Rainer,

I just checked the 2002 Conrad catalog, and your kit wasn't listed there (at least not yet?). However, there was another one: 19 28 21 on page 979. It would have had the red color (although not the user-friendly size yet), and you could have saved the 7805 because it operates on 9...15 volts.

Best regards,

Jan, who will continue browsing the catalog.

Hello Jan,

Well... shit happens... I could have saved myself a little work, but it works great now.
I had the model kit lying around at home for over a year, already assembled and soldered, but I just couldn't motivate myself to finish it.

Could you please write down the VAG part number of the blind plug located at the top of your engine cooling system? The part number is printed on the plug itself.
To be able to read the values on it, I would have to remove the splash water reservoir and other components, which would be quite a hassle to access in my case.

Best regards, Rainer.

Hi Rainer,

That also explains why the kit isn't available like that anymore. I can definitely tell you the part number, but it might take a few days. I actually had the part moved to my parents' place (there's really no room for that kind of thing in our small two-room apartment), so I can only check it out the next time I'm there.

Best regards,

Jan.

No problem, there's no rush.

Best regards, Rainer.

@ Ulf:

The idea of using operational amplifiers as impedance converters also has the additional advantage that operational amplifiers often have an offset adjustment feature. This should allow the display to be calibrated to zero at normal pressure, without the need to connect a series of diodes.

Regards,

Eike.

Hi everyone,
I've been thinking about a simple and inexpensive way to implement a digital pressure display, and I've come up with the following solution:
A 3 1/2-digit LCD voltmeter module could be used as an indicator. Such modules are available for approximately 8-14 euros (depending on the model, some may also include a backlight).
The device has a measurement range of +/- 199.9 mV with an adjustable decimal point. The input impedance is greater than 100 MΩ, which eliminates the need for a buffer circuit.
The module should ideally be powered by a 9V battery (which may optionally be switched off via a relay connected to the ignition).
A virtual ground is connected to the ground terminal. This is created using a 100 kΩ potentiometer, which is connected between the 5V terminal and the ground terminal of the pressure sensor. The wiper of the potentiometer represents the virtual ground (for adjusting the zero point).
Another 100 kΩ potentiometer is connected between the sensor output and ground. This potentiometer can be used to adjust the display so that, with a charging pressure of one bar, a voltage of 100 mV is present between the virtual ground and the signal tap of the second potentiometer.
Since the voltmeter has a very high input impedance, the impedance of the two voltage dividers becomes irrelevant. This circuit should only minimally load the signal from the pressure sensor, so that no adverse effects are to be expected.
The signal potentiometer only needs to be adjusted once. The ground potentiometer may need to be installed in a way that allows for later adjustment, as the pressure sensor appears to be an absolute pressure sensor and therefore reacts to fluctuations in air pressure, potentially displaying a high-pressure area.
The gauge would have a theoretical measurement range of -1.999 bar to .999 bar.

What is your opinion on that?

'I drive a Golf 4 with a 90 HP ALH engine. Does anyone know what color coding the wires of the pressure sensor on the intercooler have? I don't want to have to remove the water tank from the car wash to access it, and I'd rather tap into the signal somewhere in the wiring harness leading to the engine control unit.'

Well then. Doesn't work, doesn't poison!

Regards,
Eike.

Hi,

'Sorry for interrupting the electronics discussion for just a moment:'

I recently installed a (very ordinary, analog) LDA in my Golf as well.

Does something like that actually affect the vehicle's operating license?
Or also a mobility guarantee that I receive from VW for all those many, expensive inspections???

I really don't want to start a new topic for these questions...
I would appreciate any assessments or opinions.

Hi everyone,

@Markus: You probably don't need a new ABE (approval) for that. Regarding the warranty, I'm afraid I can't say anything about it, as I'm also interested in that myself.

@Everyone:

Following Eike's suggestion, I did some research. These display modules are available in a much wider selection than at Conrad, and they are also backlit, which is definitely a plus for use in a car.

Then I continued searching, and I found the pressure sensor MXP4250A for 24.30 euros. The datasheet for it is available at http://e-www.motorola.com/brdata/PDFDB/docs/MPX4250.pdf, and it explicitly states that the part is suitable for automotive applications, with turbo pressure measurements specifically listed. It measures up to 2.5 bar absolute, so it is completely sufficient.

For approximately 40 euros (because you'll also need some small additional components), you should be able to easily install a digital pressure display that is independent of the car's internal pressure sensor, and you don't need to connect anything to the existing electronics.

Best regards,

Jan.

Hi everyone,

It would probably be really ingenious if we could somehow repurpose the digital display of the clock for the LDA. However, it would be quite a significant undertaking...

@ Rainer: Do you happen to remember the color coding of the cable that carries the boost pressure signal, and possibly also the color of the 5-volt cable? My Golf 4 ALH is so tightly packed that I can't access the pressure sensor without doing some major disassembly work.

Thank you and best regards.

Eike.

Hello Eike,

I think your idea with the digital display is great; it's an elegant solution!
Regarding the cable color: I'm afraid I don't remember anymore, and it's well sealed with electrical tape, so I don't want to take everything apart to check.
Tip:
- You can find the pinout information here.
/viewtopic.php?t=562&highlight=pin+assignment+charging+pressure
- Slide the rubber cover back on the connector to reveal the pin numbers and cable colors.

Best regards, Rainer.