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  • Digital Dash Controller / Power Supply replacement effort

    Greetings all,

    As a part of my continuing effort to make my own life more difficult, I've spent the past few months reverse engineering the (early) digital cluster and it's power supply.

    You may have seen the previous links to Reddit. Now, Reddit is particularly bad about storing information (only two sites are worse, I think) so this thread will serve as a continuing documentation of my progress, while my Github will document the finished product at each stage when I'm satisfied with the result.

    As mentioned on reddit, I received the finished PCBs last weekend and then spent some time assembling them. I also received a few more filament driver demo boards, which will allow me to power and test integration with all the VFD packages (there are five) before designing the actual replacement power supply.

    About the filament driver demo boards:
    • Each one has a linear regulator and a TI push-pull driver driving a center-tapped transformer. A negative "bias" voltage is supplied at the center tap, and the result is ~2V AC heating voltage set at -18.5VDC compared to the grids and anodes. A trim pot allows the output to be precisely tuned.
    • The demo boards are actually grossly oversized due to an oversight early on. I anticipated between 800mA and 1600mA filament current (depending on the package) based on supply voltage and cold resistance. However, the filaments have a very strong positive temperature coefficient. Thus, actual current is ~100mA. As such, several components aren't needed, and the push-pull transformer can (probably) be downsized to a less expensive part than the $6 Wuerth one I had selected.
    About the compute module:
    • Teensy 3.5/3.6
    • Level-shifting bus drivers translate the 3.3V to the 5V logic expected by the display's HV shift registers
    • Parallel-in serial-out shift registers take in the 4 buttons on the front of the cluster, and the discrete inputs from the car
    • Separate ADC reads in the 7 analog signals from the car:
      • Supply voltage
      • Fuel Level 1
      • Fuel Level 2
      • Oil Pressure
      • Water Temperature
      • Manifold Pressure
      • Illumination Brightness
      • (Bonus! Power supply board temperature [planned])
    • Protected inputs for the 3 frequency signals from the car:
      • Tachometer
      • Speedometer
      • Fuel Injection Pulse Width
    • CANbus transciever available
    • SPI EEPROM/flash available for storing misc data, including replacing the odometer with a small display.
    • Supply voltages broken up in such a way that should allow powering off everything except the uC itself, which can then enter sleep mode.
    • Warning light pass through, or replacement with Neopixels
    Currently I'm working on the proof-of-life code for the compute module, which is to demonstrate successful communication with all 11 display shift registers, as well as the illumination and odometer display. From there I will progress to actually processing inputs and updating the display in a timely manner. Then comes in-car intregration, and thus dash removal. Again. Hopefully I'll have an indoor work space by that time; it's soon to be hot and muggy down here. I don't have a timeline for any of this. Eventually, yes, they will be available to the public. Not until they're good and damn ready, though.


    Ultimately, this is part of my much larger effort to develop replacements for most of the electronics in the car. As they come up they'll also be documented in the same way. Currently in queue are:
    • Time Control Unit
    • Center Gauge Pod
    • Fuel Level Conversion Unit (being developed as a General Module; I'll probably use two or three of them throughout the car)
    My lock-up control unit has already been gutted and turned into a fan controller. As everyone knows, it's best to have things spread out as far a possible from their controlled load. That makes it more interesting. That's why I also have a RasPi car computer living in that same quarter panel for AA, monitoring, and diagnostics. I also intend to either use either a Nistune'd M30 ECU, or go standalone when the turbo goes in.

  • #2
    Impressive work, I don't understand 90% of what you said, but I do want to ask, any thoughts on completely bypassing the converter for the digital fuel sender unit and allowing for the analog fuel level sender to be compatible with the digital dash? Is it possible?
    '85 2+0 Turbo

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    • #3
      That will be possible, and is actually what I intend to do for personal use.

      Note the four empty footprints under the grey connector -- these are the resistors at the top of the voltage dividers for the passive analog sensors (water temperature, oil pressure, 2x fuel level). Conventional wisdom holds that they should be equal to the value of the sensor at it's measurement midpoint (for linear curves). I elected to make these through-hole components for ease of substitution, though they do also need the higher power handling ability I think.

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      • #4
        At that point it also shouldn't be hard to use a different fuel level sender, maybe something more generic. Never know how long the stocks last for the OEM ones.

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        • #5
          Yup -- Z_Karma tabulated tank capacity vs fluid height for me, which means the only action required to retrofit a completely different sender is to mechanically adapt it.

          The same goes for all the other sensors such as GM MAP, Honeywell Oil Pressure, speed pickup, etc. The stock temperature thermistors are probably OK, but are also eligible for replacement. Just a matter of mechanically adapting (and providing the sensor supply & ground for active gauges).

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          • #6
            here a workaround for the sending unit, this works generic
            https://www.ebay.com/itm/14370981704...cad031gm700004

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            • #7
              Sorry for the radio silence. Got myself stuck into some other projects & maintenance.

              I have the power supply & data interface working for the "core 4" VFD panels. The trip meter panel, however, keeps exploding the diode used bias the filament. Even two months on I haven't found the short that *has* to be there somewhere.

              Additionally, my testing arrangement for the power supply isn't robust enough to survive going in the actual car. Too little headroom for the knockoff buck converters. Throwing together a "production" supply with real components is, unfortunately, a no-go at the moment due to the ongoing supply problems. Shoot, I can't even build a duplicate control board at the moment because I can't get any additional Teensys for the right price.

              Someday it'll work out.

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              • #8
                Due to exceptionally heavy rains last week, my basement flooded to a depth of 4.5'. This destroyed all my spinning disks and the power supplies in my server(s). The working copies of the PCB design, as well some of my notes, were stored one of those servers. Data recovery is prohibitively expensive for the spinning rust, but I'm holding out some hope that the solid states in my old desktop have previous versions that are still intact. Technically I can still reorder from OSH, but I don't think I can pull the kicad_pcb files back from them.

                This has been a brutal reminder that any backup of data stored in the same location is not a backup at all. I should have been pushing to Github, but was instead only committing to the local copy of the repository and saving to a network location.

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                • #9
                  Oh shit man, that's fucking brutal. Best of luck in your recovery efforts, not just the project files but the flooding damage in general.
                  For my home/work projects i started to share the files on Google Drive across 3 accounts, not so much for redundancy but storage limits.


                  84 AE/Shiro #683/Shiro #820/84 Turbo

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                  • #10
                    Holy cow didn't see your post! I keep everything in OneDrive or Google Drive now, nothing really local for me anymore.

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