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Where to put a brake pressure sensor?

Old 01-26-2019, 10:36 AM
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Where to put a brake pressure sensor?

Hi,

I want to add a brake pressure sensor to my datalogger. Now is the time to do it, in between seasons and with the car up on stands. Since the RX-8's ABS has control over front to rear braking force, where should I put that thing?

Thanks,
Nick
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Old 01-26-2019, 10:55 AM
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What data are you wanting? How hard you are pushing on the brake pedal, how hard the braking system as a whole is working, something else?
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Old 01-26-2019, 04:07 PM
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I put it in the line from MC to front brake input at ABS controller. If you have a DSC controller I can hook you up with the entire setup.

AC
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Old 01-26-2019, 10:16 PM
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Originally Posted by NotAPreppie View Post
What data are you wanting? How hard you are pushing on the brake pedal, how hard the braking system as a whole is working, something else?
The former. I want to log my input.
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Old 01-26-2019, 10:17 PM
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Originally Posted by Adax View Post
I put it in the line from MC to front brake input at ABS controller. If you have a DSC controller I can hook you up with the entire setup.

AC
This was what I thought Iíd just do. But Iíd be real interested to see specifically how you did yours.
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Old 01-28-2019, 10:33 AM
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Originally Posted by Mr. Pockets View Post


This was what I thought Iíd just do. But Iíd be real interested to see specifically how you did yours.
I'll take a pic tonight
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Old 01-29-2019, 08:45 AM
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Originally Posted by Adax View Post
I'll take a pic tonight
Thank you very much. I'd appreciate that.
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Old 01-29-2019, 11:52 AM
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Old 01-29-2019, 02:15 PM
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Oh that's very interesting. Is that flexible line a single part you bought?
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Old 01-29-2019, 07:45 PM
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Originally Posted by Mr. Pockets View Post
Oh that's very interesting. Is that flexible line a single part you bought?
Yes, you want it? Switched to a non DSC ABS unit which it does not work with.

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Old 01-30-2019, 08:21 AM
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Originally Posted by Adax View Post
Yes, you want it? Switched to a non DSC ABS unit which it does not work with.
I totally do. Iíll send you a PM.

Why did you seitch ABS units, and did the ECU care?
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Old 01-30-2019, 08:18 PM
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Originally Posted by Mr. Pockets View Post


I totally do. Iíll send you a PM.

Why did you seitch ABS units, and did the ECU care?
Long story but I can't get my non DSC ecu or my Adaptronic ECU to be happy with a DSC unit unless the entire DSC setup is retained (yaw sensor, steering angle sensor, switch, etc). Also some CAN Bus problems I'm trying to sort out.
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Old 01-31-2019, 02:17 PM
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Do you have any CAN dumps from your car? I'm playing with CAN on mine... but the car doesnt run yet and I don't have any CAN from a running car
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Old 01-31-2019, 06:01 PM
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I'd love to have a better understanding of the CAN and an ability to interpret a CAN dump. PM me and I can send you something if you walk me through it.
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Old 01-31-2019, 08:59 PM
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Originally Posted by Adax View Post
I'd love to have a better understanding of the CAN and an ability to interpret a CAN dump. PM me and I can send you something if you walk me through it.
You would need hardware and software that would allow you to receive the data from the bus. It's basically a lot of hex data strings that the various CAN modules send out on the bus. The signal is a 500hz one... I have figured out some of them... and I think I have enough to get the PS and dash to work for most things. I will have to find someone local time borrow the data from I guess
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Old 02-01-2019, 07:48 AM
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I may still have a CAN log somewhere...the vendor for my datalogger used it to find throttle, rpm and wheel speed.
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Old 02-05-2019, 10:13 AM
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does S2 cars have brake pressure or bake switch signal through CAN? I have AIM DL 2 and been trying to get brake signal but none of the protocol i tried worked.
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Old 02-05-2019, 05:58 PM
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Originally Posted by trackjunkie View Post
does S2 cars have brake pressure or bake switch signal through CAN? I have AIM DL 2 and been trying to get brake signal but none of the protocol i tried worked.
All DSC cars have a brake line pressure sensor but I don't know if it is accessible via CAN. You'd probably have to convert it to some usable units which would require your own sensor for calibration but I'm just guessing.
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Old 02-05-2019, 06:48 PM
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Originally Posted by Adax View Post
All DSC cars have a brake line pressure sensor but I don't know if it is accessible via CAN. You'd probably have to convert it to some usable units which would require your own sensor for calibration but I'm just guessing.
I mean, if you're just wanting to know relative number between 0 and 100%, you just have to figure out what that range is.

According to OBD Fusion with the $10 Mazda add-on pack, the ABS/TC module is on "Network B" (with the Restraint Control Module) and there is a PID for Master Cylinder Pressure. The unit options given are kPa, inHg, and psi. OBD Fusion only lets you connect two one of the two networks at a time. Apparently, the RX-8 has two CAN networks; ISO 9141 and ISO 11898 (MS/HS CAN). I guess both are made available via the plug but my hardware/software combo can only address one at a time.

FWIW, network A includes EPS, instrument cluster, ECU, remote keyleses entry and TPMS modules.
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Old 02-06-2019, 06:24 AM
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Well, ****. If we could find the PID and decode it, then None of us would need a pressure sensor.

Iíll try to find a CAN log. My car is not currently running. I wonder if I could dump one out anyway, with just the ignition on...
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Old 02-06-2019, 06:39 AM
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The catch being that you'd have to be monitoring both CAN networks simultaneously if you wanted both ECU data and ABS/DSC data at the same time. Theoretically, if your data logger doesn't support interfacing with more than one CAN bus at the same time, you could bridge the two with an Arduino and a pair of CAN shields. Just have the Arduino poll the brake pressure PID periodically via one shield and store the data. Then have it respond to polling requests for that data via the other shield.

But yah, finding the PID should be as easy as connecting your CAN logger and ELM327 to the ABS/DSC network and logging the desired PID from both devices. Then just cross reference the data to get the module ID and PID.
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Old 02-06-2019, 11:48 AM
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Originally Posted by Adax View Post
All DSC cars have a brake line pressure sensor but I don't know if it is accessible via CAN. You'd probably have to convert it to some usable units which would require your own sensor for calibration but I'm just guessing.
well that's good to know. now just have to keep bugging AIM to get it working with the DL. they have several protocol for rx8. one works with AFR and water temp but the RPM is jacked up. the other one rpm works fine but AFR and water temp doesnt work.
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Old 02-06-2019, 05:16 PM
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Originally Posted by trackjunkie View Post
well that's good to know. now just have to keep bugging AIM to get it working with the DL. they have several protocol for rx8. one works with AFR and water temp but the RPM is jacked up. the other one rpm works fine but AFR and water temp doesnt work.
Wait, I'm having the same RPM problem with my AiM, and that's all I need from it. How to you get the RPM to work? Mine only works if I disconnect the ABS unit.
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Old 02-07-2019, 07:07 AM
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That's kind of odd since the ABS/TC module is on a different CAN bus from the ECU.
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Old 02-07-2019, 07:43 AM
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Originally Posted by NotAPreppie View Post
The catch being that you'd have to be monitoring both CAN networks simultaneously if you wanted both ECU data and ABS/DSC data at the same time.
Mine can, in theory, monitor two CAN networks at once.

Granted, it hasnít event been able to read CAN and OBDII without messing with the car. So I think going the simpler route of an analog pressure sensor is the way to go.
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