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Discussion Starter · #1 · (Edited)
I haven't put this in the DIY section with the other videos as it's just a request for help.

Background:
The sensor that fails most in the PDK is the distance sensor, which is the one that senses the position of each of the shift rods. I'm trying to gather the required information so it's possible to fix the sensor yourself.

Information below regarding aftermarket sensors is current as of Dec 22.

The only replacements that seem to be available are aftermarket. Of the two I'm aware of, only one lists the price of the replacement sensor. It's made by a Canadian company XemodeX, and the list price is US$2199. It's a company that seems to specialise in aftermarket automotive products. The sensor they provide comes with a new plug, but you will need to splice your existing speed sensor into the new wiring harness they provide. I have no information regarding this sensor's performance.
Porsche PDK Shift Fork Position Sensor New | XeMODeX Inc.

The other aftermarket option, T-design, has a price of US$1890. You will need to contact the company for the pricing, as it's not listed online. Later in this thread T-design give this as the sensor price. Unlike the XemodeX sensor it doesn't come with a new plug, and requires you splice the six wires of the distance sensor onto your existing harness. I have heard good reports on the sensor's performance elsewhere online.
PDK dispacement distance gear position sensor for Porsche 7DT45 7DT70 transmission

From the research I've done it seems the required sensors to fix it would cost a few dollars only.

The OEM sensor from what I understand uses old school technology (apparently an inductive coil), and the aftermarket option uses hall sensors.

The sensor detects the position of a magnet that is attached to the shift rod. Maximum distance detected is 12.7 mm either side of a central position. Movement of the shift rod to select a gear seems to be about 9 mm either side of the central position. PIWIS shows a 7.5mm movement when a gear is selected, but it's actually about 9mm, which is easily measured via numerous other means.

The sensor gets a common 5V supply and ground with a single output from each sensor that gives the position.

EDIT: Response from the sensor is a PWM signal either apprx 1000 Hz or 860 Hz. Alternating sensors have either a 1000 or 860 Hz response. The TCM seems to measure duty cycle of the return, and is frequency agnostic. The TCM will perceive a valid and correct distance regardless of if that channel receives a 1000 or 860 Hz response.

1st video below shows my initial testing, where I thought the output was a simple DC voltage. That has consequently been found to be incorrect. It's definitely a PWM signal. Also, the TCM won't respond to a simple DC voltage. It needs to be PWM within certain parameters.

2nd video shows consequent testing and the PWM response.
3rd video shows how to test sensor outputs at the TCM
4th video shows replacement of the sensor.




 

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Great info in the video... good explanations throughout (as always with your videos!). I'm pretty good with electrical and I also have friends who are EEs that I can consult with if needed.

I guess the question is, what are you looking for? I presume you're looking for a way to replace/fix this unit? Since it's potted, I don't think fixing an existing one is in the cards for most people (though you may have the skills to do this, from what I've seen). You mentioned that the factory one uses coils... do you have detail on what those look like?

Hall sensors are certainly a better way to go, as they are off-the-shelf, usually far more durable. What you'd need is a linear hall sensor, which is designed to measure distances. Here's a quick description of how they work: https://www.electronics-tutorials.ws/electromagnetism/hall-effect.html
 

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Discussion Starter · #3 · (Edited)
I guess the question is, what are you looking for? I presume you're looking for a way to replace/fix this unit? Since it's potted, I don't think fixing an existing one is in the cards for most people (though you may have the skills to do this, from what I've seen). You mentioned that the factory one uses coils... do you have detail on what those look like?

Hall sensors are certainly a better way to go, as they are off-the-shelf, usually far more durable. What you'd need is a linear hall sensor, which is designed to measure distances.
I'm only really interested in getting out as much information as possible, and hopefully a solution or two might spring out of it. Whether that's enough information for others to fix their own sensors, someone creates a kit so you can fix your own, or someone says 'send me your sensor' and I'll fix it.

If there is something in this transmission that will fail the most likely thing is this sensor from all reports. Whilst it's good to at least have aftermarket options rather than replace the transmission completely, this seems to be priced far higher than what it would cost to do it another way.

There is a good thread on Rennlist that has been running for a number of years about how to fix the PDK. It seems to be based on information been provided from a number of sources, including workshops that work on the transmissions. Workshops are pretty cagey about giving a lot of hard earned information away, so a lot of it is speculative.

Using a linear hall sensor looks like a a very simple option. It's just finding the correct specification so the sensor response from the movement from the shift rod magnet is correct. It also needs deal with the temperatures normally seen in the transmission.

I've done a bunch of searching to find a sensor that might fit the bill, but for someone who has no experience in the field I have very little idea what I'm looking for. I don't know how to test the shift rod magnets effectively for strength so I can then find a sensor that gives a correct response over the range that is needed.

Link here to a few sensors that to my eyes look might be suitable. No idea if they are or not.
https://www.digikey.com.au/en/products/detail/allegro-microsystems-llc/ALS31000LLHALX/6624074

This one looks like the SOT 23 version mounted in the center of the sensor movement range might be what is required.
https://www.ti.com/lit/ds/sbas639c/sbas639c.pdf?ts=1668980295818&ref_url=https%3A%2F%2Fwww.google.com.au%2F
 

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Got it... makes sense.

Again, I think the temperature is attainable. I think the potting is the bigger task, but also doable.

Since you have the skills, tools, and transmission, you're certainly in a great place to perform the testing and work. I'm happy to help as best I can, and I think we can certainly put something together that could work. But you'll be the one doing all the heavy lifting, so it's totally up to you. I'm happy to help in whatever way I can. We can do this here or take it offline over email or something as well. And, like I said, one of my best friends is an EE, so I can pull in that resource... we often tackle crazy topics like this, so it's not out of the ordinary for us.
 

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Discussion Starter · #5 ·
More than happy to do the heavy lifting.

I'd like to keep the discussion here so others can contribute if able.

Below is a snip from the texas instruments sensor. Any idea which of the 5V varieties might be suitable regarding sensitivity? The shift rod magnet is a cylinder sitting on its side and running parallel to the sensor. Its 10mm diameter and 6mm long. I suspect it's either N50 or N52. It seems to be slightly less magnetic than the other N52 magnets I had on hand that I was using to test. They were N52, 12 x 14 x 3 mm. Closest the magnet will get to the sensor is about 3mm directly above. Furthest away about 12mm.


Font Material property Parallel Pattern Number
 

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I would try very hard to dig out one of the original sensor components from a defective module. It will likely have markings that can be used to identify the exact part they used, possibly through reference to an SMD marking code guide. At that point the job becomes a lot easier -- look around for a part with compatible specifications and a higher temperature rating.

Without knowing the original part number, it's going to be challenging to find a suitable replacement. You might find that a lot of different parts "seem to work," but not for long and/or not very well.
 

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I would try very hard to dig out one of the original sensor components from a defective module. It will likely have markings that can be used to identify the exact part they used, possibly through reference to an SMD marking code guide. At that point the job becomes a lot easier -- look around for a part with compatible specifications and a higher temperature rating.

Without knowing the original part number, it's going to be challenging to find a suitable replacement. You might find that a lot of different parts "seem to work," but not for long and/or not very well.
The original sensor is reported to be a coil, not a hall sensor. We're trying to make it a hall, as there is an aftermarket company who has done this. Our effort is simply to see if we can get there, publicly, so others can do this work themselves as well.

@jjrichar As for the spec. First step, are you sure you're getting 5V from the car-harness for these coils? If so, then yes we can run a 5V sensor... otherwise we may have to put in some voltage regulators or something. Can you confirm what voltage the car delivers?

As for actual components, I would get a few of them (they are low cost) and see if anything gets us close to start with. I think the key spec to watch is the temperature, to find something that is well tolerant. I don't think we can guess at the specs otherwise, since we're coming from non-hall to hall-sensors anyway... but after testing a few you may find one that works, or something that gives us guidance as to what is most important. For example, you mentioned the magnet feels weaker, so a "longer range" one may be needed, so that it's more sensitive to the weaker magnetic field. That's why it's best to grab a few and try them, I think. Be sure they're "linear" hall sensors, of course.

If you still want to dive into specs, then we can consider trying that... I'd need to know what distance we're dealing with between where the magnet is and where the sensor "would be" inside the potting.

It might be good to get a bad assembly, and clear out the epoxy so you can see what space you have to work with inside. This would also give you a way to build test assemblies and double-stick-tape sensors at varying heights or something, so you can try various distances as well.

I think this needs to be an iterative exercise, as we are going off-script for what the original part did... but I can dive into math if we really have to go that way.
 

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Discussion Starter · #8 ·
The original sensor is reported to be a coil, not a hall sensor. We're trying to make it a hall, as there is an aftermarket company who has done this. Our effort is simply to see if we can get there, publicly, so others can do this work themselves as well.

@jjrichar As for the spec. First step, are you sure you're getting 5V from the car-harness for these coils? If so, then yes we can run a 5V sensor... otherwise we may have to put in some voltage regulators or something. Can you confirm what voltage the car delivers?

As for actual components, I would get a few of them (they are low cost) and see if anything gets us close to start with. I think the key spec to watch is the temperature, to find something that is well tolerant. I don't think we can guess at the specs otherwise, since we're coming from non-hall to hall-sensors anyway... but after testing a few you may find one that works, or something that gives us guidance as to what is most important. For example, you mentioned the magnet feels weaker, so a "longer range" one may be needed, so that it's more sensitive to the weaker magnetic field. That's why it's best to grab a few and try them, I think. Be sure they're "linear" hall sensors, of course.

If you still want to dive into specs, then we can consider trying that... I'd need to know what distance we're dealing with between where the magnet is and where the sensor "would be" inside the potting.

It might be good to get a bad assembly, and clear out the epoxy so you can see what space you have to work with inside. This would also give you a way to build test assemblies and double-stick-tape sensors at varying heights or something, so you can try various distances as well.

I think this needs to be an iterative exercise, as we are going off-script for what the original part did... but I can dive into math if we really have to go that way.
Definitely 5V. It has this on the wiring diagram and it also gives the voltage value in PIWIS.

The texas instuments sensors are designed for automotive applications, with a rated temp or -40 to 150 C. I haven't been able to find anything better than this so I assume this would be fine. It's definitely a linear sensor. So it might be just a case as you say of getting some and having a play to see the response.
 

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-40 to 150C is great... yeah, I'd say get a couple of those and run with it.

As you noted, initially speaking, it may not operate in the "direction" you want, and we can fix that. The first test would be to see if you can get it to have a similar "span" for voltage (regardless of direction/polarity) when at an appropriate distance (hence digging out space in an old part so you can space it as necessary).

Keep in mind that you may be able to change the direction by orienting the sensor in different directions - ie flipping it over or spinning it 180-degrees may fix that as well... but if not, it's easy enough to fix that with circuitry.
 

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Discussion Starter · #10 · (Edited)
-40 to 150C is great... yeah, I'd say get a couple of those and run with it.

As you noted, initially speaking, it may not operate in the "direction" you want, and we can fix that. The first test would be to see if you can get it to have a similar "span" for voltage (regardless of direction/polarity) when at an appropriate distance (hence digging out space in an old part so you can space it as necessary).

Keep in mind that you may be able to change the direction by orienting the sensor in different directions - ie flipping it over or spinning it 180-degrees may fix that as well... but if not, it's easy enough to fix that with circuitry.
Ordered some sensors from mouser. Can you have a look at the doc in the link below. Stuff I don't really have a full understanding of is the specifics of the circuitry. It seems a capacitor (1 microfarad) needs to be placed in parallel with Vcc and ground and it also talks about an additional resistor. I'll be using 4 sensors in parallel. Do I need a single capacitor of the same capacity or do I need something larger/smaller. From my understanding the capacitor is to control the initial buildup of current when it's turned on. Correct? Can you give me a basic description of what is required and why. Thanks

https://www.ti.com/lit/ds/symlink/drv5055-q1.pdf?ts=1669240411148&ref_url=https%3A%2F%2Fwww.ti.com%2Fproduct%2FDRV5055-Q1%3FCMP%3Dconv-poasamples
 

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For now, I wouldn't worry about the "optional noise filter"... chances are, there is filtering present in the car already, and if there isn't we can visit that later. The resistor is for "fault detection" which we don't need either.

The cap at the voltage input is just to provide some basic filtering from noise on the input voltage. On a bench, you won't likely have much of this anyway, but it doesn't hurt to have a cap to start out with. Note that it says minimum of 0.01uF. Since you're using multiple sensors, you can certainly go higher and use a single to cover them all. Whatever you have above 0.04uF would be fine, I'm sure... don't overthink it, haha.

Be sure the sensors are all wired parallel to the Vcc and ground... don't wire the sensors in series. (You said you were doing this, but I just want to make sure you keep doing it, haha.)

A few other comments from the manual:
1) Note that the device "switches" internally between two different operating voltages... and that changeover happens right at 4.5V. For this reason, I'd recommend getting a true 5V power supply instead of the 3x 1.5V batteries you've been using so far. A typical USB charger should be able to get you this (get a USB cable and cut the end, if needed)... you may have other options, of course. Ideally, if you can get a true benchtop power supply, that might be ideal... because the USB chargers can be VERY noisy.
2) Note there are 5 different versions of these sensors (A1-A5)... not sure which one you are getting, but be aware of this.
3) Section 8 in the manual is worth a quick read... they give you some guidance on how these sensors are intended to be used, orientations to the field, etc... something we should keep in mind as we work forward.

Our first step goal is to get the proper voltage range for the car's expectations. This is where spacing and orientation is important, so that's the first challenge - can we voltage movement at the ranges we have with the existing magnets. Once we get movement, we can adjust the voltage to meet what the OEM delivers via external circuits... so let's focus on the first thing - getting voltage movement.

One thing that might help is to test with the OEM part and see what the range is for the voltage. So, while you're waiting for sensors to arrive, put the OEM part back in, and see what you get for voltage ranges at varying shift positions. I don't recall if PIWIS will tell you this, but you can also probe this with a volt-meter if that's easier for you. See if you can record the min/max in actual operation for each sensor (remember, we want actual shift positions, not the full range of the sensor... so maybe you just do this with your working trans in the working car setup?) If you can't get them all, that may be ok... get what you can.
 

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Discussion Starter · #12 ·
For now, I wouldn't worry about the "optional noise filter"... chances are, there is filtering present in the car already, and if there isn't we can visit that later. The resistor is for "fault detection" which we don't need either.

The cap at the voltage input is just to provide some basic filtering from noise on the input voltage. On a bench, you won't likely have much of this anyway, but it doesn't hurt to have a cap to start out with. Note that it says minimum of 0.01uF. Since you're using multiple sensors, you can certainly go higher and use a single to cover them all. Whatever you have above 0.04uF would be fine, I'm sure... don't overthink it, haha.

Be sure the sensors are all wired parallel to the Vcc and ground... don't wire the sensors in series. (You said you were doing this, but I just want to make sure you keep doing it, haha.)

A few other comments from the manual:
1) Note that the device "switches" internally between two different operating voltages... and that changeover happens right at 4.5V. For this reason, I'd recommend getting a true 5V power supply instead of the 3x 1.5V batteries you've been using so far. A typical USB charger should be able to get you this (get a USB cable and cut the end, if needed)... you may have other options, of course. Ideally, if you can get a true benchtop power supply, that might be ideal... because the USB chargers can be VERY noisy.
2) Note there are 5 different versions of these sensors (A1-A5)... not sure which one you are getting, but be aware of this.
3) Section 8 in the manual is worth a quick read... they give you some guidance on how these sensors are intended to be used, orientations to the field, etc... something we should keep in mind as we work forward.

Our first step goal is to get the proper voltage range for the car's expectations. This is where spacing and orientation is important, so that's the first challenge - can we voltage movement at the ranges we have with the existing magnets. Once we get movement, we can adjust the voltage to meet what the OEM delivers via external circuits... so let's focus on the first thing - getting voltage movement.

One thing that might help is to test with the OEM part and see what the range is for the voltage. So, while you're waiting for sensors to arrive, put the OEM part back in, and see what you get for voltage ranges at varying shift positions. I don't recall if PIWIS will tell you this, but you can also probe this with a volt-meter if that's easier for you. See if you can record the min/max in actual operation for each sensor (remember, we want actual shift positions, not the full range of the sensor... so maybe you just do this with your working trans in the working car setup?) If you can't get them all, that may be ok... get what you can.
Lots of good stuff for me to think about while the sensors are in the mail.

I ordered a few of each of them. A5 is just a reverse version of A1, so I didn't bother with it.

You don't get the voltages for each of the sensors in PIWIS, just the position. You do get the input voltage, which was a little over 4.8V from TCM in the project car. I'll see what I can get.

Figure 21 in section 8 is exactly the way it will be installed. It seems that it's just a case correct orientation reference the magnet and then finding the correct sensitivity to get the correct voltage response.
 

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Lots of good stuff for me to think about while the sensors are in the mail.

I ordered a few of each of them. A5 is just a reverse version of A1, so I didn't bother with it.

You don't get the voltages for each of the sensors in PIWIS, just the position. You do get the input voltage, which was a little over 4.8V from TCM in the project car. I'll see what I can get.

Figure 21 in section 8 is exactly the way it will be installed. It seems that it's just a case correct orientation reference the magnet and then finding the correct sensitivity to get the correct voltage response.
Hi jjrichar,

The ZF distance sensor output is pulse width modulation whereas that TI sensor (DRV5055) has an analog output. You could use it but then you need another chip to convert it to PWM. (PWM outputs a modulated signal with the pulse width proportionate to the signal level).

The TI DRV5057 sensor has a PWM output but unfortunately it's locked at 2 KHz. The ZF distance sensor output is 1 kHz (I measured it) so that TI part won't work. I have not found a simple Hall Effect sensor that outputs PWM at 1 kHz.

The other option is to use a programmable Hall Effect sensor like those available from Melaxis. The nice thing about these is you can set their PWM output frequency and sensitivity using the programmable interface. You can also set things like temperature compensation to correct for temp variation. Plus it's all in one package.

So there are two options:
1) Use a simple HE sensor (like the TI DRV5055) with an additional analog to PWM convertor (like an Analog Devices LTC6992)
2) Use a programmable Hall Effect output sensor with PWM like the Melaxis MLX90364

The issue with all of this is parts have to be selected that properly scale the magnetic flux to the output signal, so you'll probably have to play with different HE sensors in the DRV5055 family to find the right one. On a programmable part you can set this directly on the component and experiment.

I sent you an email with some additional info and will post more here. I'll probably mirror it over on my Rennlist PDK thread as things progress.

Edit: Just watched your video, good stuff as I didn't realize you had one out of the car already. You need to measure it with an oscilloscope so you can see the pulse, a multimeter isn't sufficient and will give confusing results. Take a look at the video I posted in the next comment.
 

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Discussion Starter · #16 ·
Apologies for the poor initial information. After testing using different modes on my multimeter, this is what I found it's clearly a PWM signal. Making a quick video to show all that I found. It's a bit wacky how it's all setup.
 

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Exactly, that's why I was suggesting taking one apart and trying to identify the actual component, if possible. Guesswork isn't what's called for here.

FWIW, if the outer shell is aluminum, I can X-ray it if someone wants to send one up here (Pacific NW). That could potentially identify the part, or at least narrow it down.
 

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Exactly, that's why I was suggesting taking one apart and trying to identify the actual component, if possible. Guesswork isn't what's called for here.

FWIW, if the outer shell is aluminum, I can X-ray it if someone wants to send one up here (Pacific NW). That could potentially identify the part, or at least narrow it down.
Appreciate the input but we aware of the internal components of the OEM sensor. Go to the link below and then click on the 'detailed failure information' tab. It has an X ray of what is in the OEM sensor as well as what's in the aftermarket version.

The OEM is from what I understand seriously old school, with sensors superseding it since that are vastly cheaper and more reliable. Hence why the aftermarket solutions use these and why we are investigating this route.

Porsche PDK Shift Fork Position Sensor New | XeMODeX Inc.
 
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