Ambient Pressure Sensor: Build a Replacement Circuit

Hello everyone,

Since it has proven quite difficult to obtain a replacement sensor, I would now like to try building a replacement circuit. As I have read in this forum, this can be achieved using resistors or a potentiometer. Personally, I would prefer to use a potentiometer.
Can someone explain to me what kind of potentiometer I need and how it should be installed?


Greetings.
Reuselkopp.

Hello everyone,

Does anyone have any ideas? Where are the electronics specialists?

Greetings.
Reuselkopp.

I have a faulty MSA15 pressure sensor lying around at home, and the sensor itself is still working. When I have time, I'll desolder it and measure the resistance values for approximately 1005 mbar (which is the standard value used here).

Here's the translation:

"Tip: It's best to solder flexible wires into the solder pads on the circuit board, and then connect the replacement resistor to those wires. These components don't like it when you experiment with them, and the same solder joint is heated repeatedly."

Hello VW enthusiasts,

"Glad to hear from you. I'd also be interested in buying the working sensor from you. However, I'm sure we can also find a suitable potentiometer based on the measured values."

Regards,
Reuselkopp.

Let's see if I can get this done. I mean, I used up my last desoldering wick. This will be interesting .

Quote:

and measure the resistance values for approximately 1005 mbar (which is common for us).

You can stop now, because something exciting is about to happen.

It has a DMS (presumably a Digital Multimeter System) built in, and it's powered by +5V and 0V through the external pins. Depending on the resistor value, a higher or lower voltage appears at the middle pin, but it's always below 5V.

EDIT: The middle connector is only the signal output for the boost pressure sensor, not for the ambient pressure sensor .

Does anyone know the pin assignments for pins 30, 31, and 15 on an EDC15VM+? I have a working one in the office, and it should be similar; unfortunately, I can't find my documentation for it (yes, it's my fault ).
Then I could quickly measure that. Hopefully, the power supply cable from the EVC will fit .

EDIT: I was mistaken - the EDC15 already has a sensor with internal logic.

A faulty MSA15 (with bad solder joints on the EEPROMs) was eventually found.

I'm measuring something right now...

@vwschrauber

Hooray!

Thank you for your effort.

Regards,
Reuselkopp.

Okay, I've got it now.

Starting from the connector side of the MSA15, the first pin of the ambient pressure sensor is ground.
The second pin is +5V, and the last pin is the signal output.

WARNING: The charging pressure sensor behaves differently:
1. +5V
2. Signal.
3. Mass.

At an ambient pressure of 948 millibars, the signal output of the pressure sensor reads 3.71 volts.


The voltage reading on the load cell sensor is 1.67V, and it increases to 1.85V when air is blown into it.


One could design a voltage divider for the 3.7 volts, or simply try connecting two silicon diodes in series in the forward direction and powering them with +5V.

Voltage divider: The voltages will be proportional to the resistances. I would choose relatively high resistance values to avoid interfering with the 5V voltage level of the control unit or damaging the voltage regulator.

That would look something like this:
Resistance from signal output to ground: 740 ohms, or the nearest value in the E12 or E24 standard series.
Output signal resistance to ground: 260 Ohms.

Alternatively, a 1k potentiometer can also be used, but it cannot be directly soldered in because the signal output is not centered.

Attention: The 3.7 volts correspond to 948 millibars. In some software versions, the boost pressure limit may already be activated at this value! Ideally, this value should be adjusted using a potentiometer to approximately 1010 millibars.

"For those who don't want to work directly on the car, it's also possible to connect the k-line to a Hex-USB or Hex-RS232 interface, connect the control unit to the interface, supply the interface with power, and adjust the value directly at the desk."
To power the sensors, simply connect the ground wire to the wider pin at the boost pressure connection, and connect +12V to the wider pin on the opposite side.

The error memory will obviously be full, since the car is missing.

The "power supply cable for all control units except Bosch" from EVC, along with its corresponding power adapter, provides excellent service.

Hello Reuselkopp,

Use a simple, high-impedance potentiometer with a linear taper (this is standard, although logarithmic tapers are also available). A potentiometer in the 10kOhm range should work well.

Connect the two outer terminals to the 0V and 5V pins of the former altitude sensor, and connect the potentiometer terminal to the former altitude sensor output. Before powering on the MSA, ensure the potentiometer is in the middle position.

Then:
- Connect the MSA.
- Read ambient pressure using VCDS.
- If necessary, adjust the potentiometer until the desired ambient pressure is displayed.

Edit: Oops, someone was faster than me...

Regards,
Sure, here's the translation:

"Guste" is a German word that means "gust" or "gust of wind." It can also be used to describe a sudden burst of something, such as laughter or anger.

@guste: I think 10k is a bit too high.

With a current of 1k, you have a leakage current of 5mA, which results in a power loss of 25mW.

@vwSchrauber: You're probably right that 10k was a relatively high resistance value, and I'm also aware that the voltage at the potentiometer's output will be different without the following circuit compared to when the circuit is connected.

But: None of this matters, because even if the evaluation electronics, for example, had a pull-down resistor of only 1k, Reuselkopp, with a connected 10k potentiometer, could still adjust to any desired voltage . Of course, it would be a different potentiometer position than with a 1k potentiometer, but any desired voltage would still be adjustable.

I suspect that the original sensor will only be able to provide a maximum of a few milliamperes, and therefore the evaluation electronics will have a very high impedance.

Okay, Reuselkopp: Just grab any potentiometer with a value of 1k or 10k, it will work. Just don't go any higher or lower in terms of powers of ten.

Regards,
Sure, here's the translation:

"Guste" is a German word that means "gust" or "gust of wind." It can also be used to describe a sudden burst of something, such as laughter or anger.

Hi Moshe,

That sounds quite easy to implement. If I understand guste100 correctly, it doesn't matter which potentiometer I use, as long as it's between 1k and 10k ohms.

Could I get the "SPINDELTRIMMER-1-W-1K" in the 5K version (the "goldene Mitte" - golden mean)?

Greetings.
Reuselkopp.

Yep, with that, you can adjust the ambient pressure or altitude with an accuracy of approximately +/- 1 meter .

Regards,
Sure, here's the translation:

"Guste" is a German word that means "gust" or "gust of wind." It can also be used to describe a sudden burst of something, such as laughter or anger.

Quote:

But: None of this matters, because even if the evaluation electronics, for example, had a pull-down resistor of only 1k, Reuselkopp with the connected 10k potentiometer could still adjust to any desired voltage icon_wink.gif.

It would, of course, be a different potentiometer position than with a 1k potentiometer, but any desired voltage would still be adjustable.

Yes, you are right, the resistance track itself is actually irrelevant. 10k resistors just require a steadier hand for adjustment }.