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Thread: Feeler: Open Source OBC Firmware

  1. #551
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    Quote Originally Posted by m2pc View Post
    ... Next is the vehicle speed signal, does anyone have any info on that?
    On an E36, it's an active low pulse with a K-Zahl [K-count] of 4712 pulses per kilometer.
    Last edited by johnf; 09-11-2010 at 03:10 AM.

  2. #552
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    Johnf -- perfect, thank you very much!

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  3. #553
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    Quote Originally Posted by johnf View Post
    On an E36, it's an active low pulse with a K-Zahl [K-count] of 4712 pulses per kilometer.
    Is this a square wave signal? I noticed on the stock OBC logic board, this signal goes through a diode, is pulled to +12V with a 10K resistor, then fed into the input of a 7414 Schmitt trigger IC via a 100k series resistor. I wonder if we need this with the openOBC, or if I can simply route it to one of the counter inputs, skipping the 7414?

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  4. #554
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    It's a narrow pulse which I filter in my designs. One design uses a 75 µs hardware, single-pole, RC filter feeding a falling edge triggered interrupt (the e-folding time could be longer: I'm using the same design to measure ABS wheel speeds); the other counts multiple, unfiltered samples with a software up/down counter filtering each pulse. I'll see if I can find the numbers for the latter because I only used it for the cluster vehicle speed signal, and have verified it to at least 210 km/h (on the same Autobahn Mercedes uses ).
    Last edited by johnf; 09-14-2010 at 09:13 AM.

  5. #555
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    Quote Originally Posted by johnf View Post
    It's a narrow pulse which I filter in my designs. One design uses a 75 µs hardware, single-pole, RC filter feeding a falling edge triggered interrupt (the e-folding time could be longer: I'm using the same design to measure ABS wheel speeds); the other counts multiple, unfiltered samples with a software up/down counter filtering each pulse. I'll see if I can find the numbers for the latter because I only used it for the cluster vehicle speed signal, and have verified it to at least 210 km/h (on the same Autobahn Mercedes uses ).
    With the 74HC14 that was used, only 2 of the 7 elements were actually used, with 5 wasted inverters just left disconnected. A simple RC filter would be low cost and perfect to feed into one of the counter trigger pins on my PIC chip.

    Care to share any design tips? It's for a good cause

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  6. #556
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    Which ones? I could probably spend days writing down tips and suggestions.

  7. #557
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    Quote Originally Posted by johnf View Post
    Which ones? I could probably spend days writing down tips and suggestions.
    On how you converted the vehicle speed signal into something suitable for a microcontroller. I was just going to use a 74HC14 as the OEM design used, but I'm curious how others have done it.

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  8. #558
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    A 74HC14 is probably more rugged and tolerant, but nothing stops you from feeding your outside signals to a microcontroller's inputs without the buffering, if you respect the inputs' limitations.

    I apply 12V signals through a 100K + 100K voltage divider, with a filter capacitor on each edge-sensitive inputs between the input and ground. (The microcontrollers I use have schmitt trigger inputs.) The divider may force a small continuous current into an input, but it's comfortably below the 0.5-1 mA currents that might cause ion-migration failure.

    The divider's resistance may also be high enough that, say, an 80V surge into the input(s) won't excessively raise the logic supply voltage. Whether it does depends on your chip's operating current during the surge. If it's less than the current from the surge, the chip will just draw some of its operating current through the input(s) rather than from the voltage regulator.

    Once you get your signal to the micrcontroller input, you have many ways to count its pulses and convert them to speeds, but I assume you've already sorted that out?

    For the controller I verified to 210+ km/h, I sample the unfiltered vehicle speed signal 9600 times a second, and flip the filtered input state to active when the raw signal's been low for four more samples than it's been high, and to inactive when it's been high for four more samples than it's been low.

    [Writing the above prompted me to check some rate pulse counting code and to discover a long standing overflow problem in its simulation which disappeared when I substituted the actual code from the target.]
    Last edited by johnf; 09-15-2010 at 03:43 PM.

  9. #559
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    Quote Originally Posted by benemorius View Post
    Does anyone have precise measurements for the board dimensions and the cutout positioning?
    Hi All!

    Yes, I did measured the stock board. Actually I have an update, I am done with my first version of the PCB.

    I will give it a couple of touchups before ordering on expressPCB. Mostly I have to replace the GPS antenna connector to an MMCX and i think that is it. I printed a cardboard and cut it out to compare to the stock and I think I am in the money.

    I think i will go with the package of 4 boards and no silkscreen to start. This means there will (may) be 4 prototypes.

    Also i'll start by ordering all semiconductors (MCU, pheripheral ICs) and hold off on the purchase of the modules which are more expensive until I am at a point where the thing is alive and responding thorugh the serial port on the expansion connector (the expansion connector doubles as a development COM port access).

    Let me know your comments.

  10. #560
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    Update from my neck of the woods:

    I've spent considerable time tracing out all of the connections on the OEM board, so I can be 100% sure my interface is compatible with all E36 model years that this OBC fits in. Where I work there is a very good EE that I've been collaborating with and bouncing ideas off of -- he's had some very valuable insights that I'm incorporating into what will become the openOBC reference design.

    Earlier this week I took a few test drives with an oscilloscope riding shotgun, to visualize and capture exactly what the ambient light signal, fuel consumption, and road speed signals looked like. These have been added to the openOBC Wiki.

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  11. #561
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    At the moment, all I can find of the wiki is the software functions and fuel level signal.

    I am curious just how bright it has to get before the ambient light level signal starts pulsing.

  12. #562
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    Quote Originally Posted by johnf View Post
    At the moment, all I can find of the wiki is the software functions and fuel level signal.
    This Wiki software is a bit strange... anyhow, I added a link on the home page to the "File Galleries" which should allow you to drill down and see the scope captures. Look under "Wiring Diagrams" and the appropriate sub-folder.

    Quote Originally Posted by johnf View Post
    I am curious just how bright it has to get before the ambient light level signal starts pulsing.
    On the contrary, it seems that the signal pulses only when the light level diminishes; at full sun it appeared to have no pulsing at all.

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  13. #563
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    That's funny. Maybe I had my scopemeter hooked up backwards. With the ignition on (position 1), I measured a constant 12V in the dark and then had to shine light on the sensor to get active low pulses.

    I'll point Firefox and Safari at the Wiki and see if they can drill.

    EDIT: I was able to access the figures through the File Gallery link. Thanks for adding that!
    Last edited by johnf; 09-24-2010 at 03:50 PM.

  14. #564
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    Quote Originally Posted by johnf View Post
    That's funny. Maybe I had my scopemeter hooked up backwards. With the ignition on (position 1), I measured a constant 12V in the dark and then had to shine light on the sensor to get active low pulses.

    I'll point Firefox and Safari at the Wiki and see if they can drill.

    EDIT: I was able to access the figures through the File Gallery link. Thanks for adding that!
    Strange... I also noticed the Interior Light Switch (X1070/Pin 16) was a 100Hz signal with ~4% duty cycle at full bright and ~80% duty cycle at full dim. I'm assuming this signal is used to "gate" the backlight driver such that it has a constant 'on' time but varying 'off' PWM, is this what you've found?

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  15. #565
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    X1070 pin 16 is the ca. 20-100% duty cycle dimmed illumination power (58g) that is set and supplied by the dimmer control. It powers, among other things, the bulbs and LEDs that illuminate the console switches and controls. I have always assumed it goes straight to the twist-in incandescent bulbs that illuminate the various MIDs, including the OBC.

    I was measuring the instrument cluster light sensor signal the cluster feeds to X0170 pin 15. It was 12V (100% on) in the dark and PWM modulated down to 0V (0% on) when I shined the BMW glovebox flashlight on the sensor. That brightened the LCD text.
    Last edited by johnf; 09-24-2010 at 04:53 PM.

  16. #566
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    Quote Originally Posted by johnf View Post
    X1070 pin 16 is the ca. 20-100% duty cycle dimmed illumination power (58g) that is set and supplied by the dimmer control. It powers, among other things, the bulbs and LEDs that illuminate the console switches and controls. I have always assumed it goes straight to the incandescent bulbs that illuminate the various MIDs, including the OBC.
    On the stock OBC, this line goes through a diode, then through a 120 Ohm resistor and then directly to the anode of the keypad backlight, which is 4 SMD LEDs in series to ground. The backlights for the OBC main and clock displays are both driven through power MOSFETs from the MCU and possibly tied into X1070 pin 15 as well.

    Quote Originally Posted by johnf View Post
    I was measuring the instrument cluster light sensor signal the cluster feeds to X0170 pin 15. It was 12V (100% on) in the dark and PWM modulated down to 0V (0% on) in bright light.
    I will check this again. The MIDs and OBC displays are supposed to track ambient light (get brighter with higher ambient, and dim themselves in the dark). So the signal may be a normally-high, active-low PWM signal.

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  17. #567
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    All I can say is...wow....just WOW. You guys are my heroes. I'd love to have an OBC that could actually do useful stuff. Didn't get to read through all 20+ pages of this thread, but it would be sweet if you could have some kind of audio interface as well. One where you would you be able to display audio info (track name, artist, etc.) on the OBC display. Or, how about display of the radar detector info from a Valentine 1 (like the StealthOne)?
    I wish I could help or contribute in some way, but this kinda work is WAY over my head. My brain thinks in gears and moving parts...not in 0's and 1's...
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  18. #568
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    If you guys could get boost, egt, afr, water temp etc then I would love to have this.

  19. #569
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    Little update from me: This project is back on my "active" list again!
    I had to take care of some maintenance items on my M3, then got busy with other projects. Good thing is, some of those other projects will port directly into my openOBC efforts.

    Regarding comments above: yes, it's very possible to interface with an iPod/iPhone/mp3 player to show track names. V1 integration is also planned and we have a unique approach for this as well. Stay tuned!

    Spoiler alert: The openOBC project has spawned a few other side projects for me: 1) Touchscreen Linux OBC, and 2) LCD digital E36 cluster! Stay tuned!

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  20. #570
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    Quote Originally Posted by m2pc View Post
    Little update from me: This project is back on my "active" list again!
    I had to take care of some maintenance items on my M3, then got busy with other projects. Good thing is, some of those other projects will port directly into my openOBC efforts.

    Regarding comments above: yes, it's very possible to interface with an iPod/iPhone/mp3 player to show track names. V1 integration is also planned and we have a unique approach for this as well. Stay tuned!

    Spoiler alert: The openOBC project has spawned a few other side projects for me: 1) Touchscreen Linux OBC, and 2) LCD digital E36 cluster! Stay tuned!
    Its frustrating being a second year electrical engineering student and I cannot contribute to this at all

  21. #571
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    Quote Originally Posted by Dricebrug View Post
    It's frustrating being a second year electrical engineering student and I cannot contribute to this at all
    I was being paid to do electronic design and firmware before I started university. I think you are being unduly pessimistic about your talents. Either that or that you may find they are better applied in other fields, for example, in finance or management. (Both can certainly be much better supported and more lucrative.)

    If I were in your shoes, I'd find a piece of the project that looks like fun and needs work, read up on how it's done and just start doing it! You won't know that you can until you do. Just my two cents worth of pep talk.
    Last edited by johnf; 10-30-2010 at 07:23 AM.

  22. #572
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    Quote Originally Posted by Dricebrug View Post
    Its frustrating being a second year electrical engineering student and I cannot contribute to this at all
    Why not pick yourself up a used 18-button OBC and go to town? I'm sure you have some resources available at the university you can tap into, like an electronics lab with decent oscilloscopes!

    Keep in mind, what I'm building here is a "reference design". It's designed to allow others to either a) build what I've built, or b) build their own designs, based on their own skills and goals.

    There's already at least 3 versions of this being developed, one by myself, one by benemorious, and one by mefis. We certainly have room for more!

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  23. #573
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    Major Update!

    I quickly realized it would be a huge task to prototype the openOBC by hand using a solder breadboard, so I have completed drawing the PCB for the v1.0 reference design:


    Features:
    - All through-hole design (no surface mount parts)
    - Basic OBC functions plus interface to vehicle diagnostic bus
    - Expansion via 2 connectors
    - High-efficiency switching DC-DC power supply for +5V
    - Low-dropout voltage regulator for +3.3V and +5V standby

    The expansion board (not drawn yet) mounts on top of the main PCB to expand the openOBC functionality:

    - Power (+12V, +5V, +3.3V) and GND connections
    - SPI bus
    - 3 SPI address pins (up to 8 SPI devices)
    - Serial-to-parallel driver expansion bus (for driving relays, etc.)
    - 4 10-bit A/D channels for external sensors
    - Dual CAN bus for even further expansion

    The expansion board reference design I've designed includes:

    - Bosch BMA180 3-axis accelerometer
    - Sparkfun 66-channel GPS receiver
    - 8 relay outputs
    - Prototyping space (plated through hole breadboard area)

    Once I finish verification of my main board, I will be ordering a sample run from the PCB manufacturer and building the first real prototype.

    Things are about to get very exciting!
    Last edited by m2pc; 12-27-2010 at 07:23 PM.

    1999 ///M3 TiAg | Heated Power Vaders | DDM Projector36 5000K 55W HIDs | DDM 3000K 35W HID Fogs
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    E36 OBC is now open! Join the effort: BF.C Thread | openOBC Wiki

  24. #574
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    That looks fantastic!

    Great to see progress!

  25. #575
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    Nice! Looks great! Anxiously awaiting the outcome of this! Keep up the great work!
    Alvin Caragay
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    '96 AC Schnitzer S3 Sport CLS Replica (https://www.facebook.com/ACSS3SportCLSR)
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