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Thread: Fusion Brain CarPC LT1 dash gauges project

  1. #11
    Constant Bitrate ACCLR8N's Avatar
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    Frequency boards are in. RPM is connected to port 0, port 1 is set aside for speed. Virtual screen is showing 0 to 0.01V with key on engine off. There seems to be a lot of interference when the engine is running and ports 0 & 1 parallel each other. I shorted port 1 AIN to the ground as suggested and that lowered the read out but they still both bounce the same 0.2V with engine running. The tach multi-image is slow to rev, and the port spikes over 3 volts when I let off the gas. Moving the USB around seems to alter the tach. Open to suggestions.

  2. #12
    Fusion Brain Creator
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    Quote Originally Posted by ACCLR8N View Post
    Frequency boards are in. RPM is connected to port 0, port 1 is set aside for speed. Virtual screen is showing 0 to 0.01V with key on engine off. There seems to be a lot of interference when the engine is running and ports 0 & 1 parallel each other. I shorted port 1 AIN to the ground as suggested and that lowered the read out but they still both bounce the same 0.2V with engine running. The tach multi-image is slow to rev, and the port spikes over 3 volts when I let off the gas. Moving the USB around seems to alter the tach. Open to suggestions.
    Multi image slow to react: you probably have averaging turned on.

    It sounds like there's insufficient filtering for your tach signal. Where are you grabbing it from? What's its peak to peak voltage like? Have you put an o-scope on it?

  3. #13
    Constant Bitrate ACCLR8N's Avatar
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    Nope, averaging is false and history is set to zero. I'm hooked to the feed from the PCM to the gauge cluster. No gauge cluster of course. Don't own an ocilloscope.

  4. #14
    Fusion Brain Creator
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    Quote Originally Posted by ACCLR8N View Post
    Nope, averaging is false and history is set to zero. I'm hooked to the feed from the PCM to the gauge cluster. No gauge cluster of course. Don't own an ocilloscope.
    Are the unmodified boards any better?

    0.2v is 5% of full scale, which should be what, 250rpm? it's far from ideal, but might be the best that can be done at this (hobbyist) level.

  5. #15
    Variable Bitrate
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    I have a 95 LT1 and I get all kinds of data out of the OBD port. I use Datamaster.

  6. #16
    Constant Bitrate ACCLR8N's Avatar
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    I don't have an unmodified board, I'm running the Tach off 900K ohms. I want to try cranking up the sample rate. Looking at the timer page, are those values Hz? What is the max value, 180? This is global, can I adjust the rate just for port 0?

    I've not found any documentation on the board except the one post showing an engineering layout. I have my Tach signal from PCM connected to the post below the "IN", the other is chassis grounded. My 3-pin 5V is connected below "OUT", my add on resistor is grounded to the middle pin and the lowest pin is FB AIN.

    Edit: Found PCM operates the coil through a 5V squarewave on the negative side of the coil, but nothing on the tach output other than it is "clean" and 4 pulses per revolution. So my tach should be reading 4x's higher. Thinking I need to hook FB 5V to + in and tach signal to in ground.

  7. #17
    Constant Bitrate ACCLR8N's Avatar
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    Quote Originally Posted by turbochris View Post
    I have a 95 LT1 and I get all kinds of data out of the OBD port. I use Datamaster.
    I don't think you can do pretty pictures with that. The OBD port doesn't provide oil pressure, fuel level, fuel pressure or idiot lights that I'm looking for. When my scanner is connected, the check engine light is on and the fans run. Does Datamaster do that?

  8. #18
    Constant Bitrate ACCLR8N's Avatar
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    Tachometer and speedometer problem: After some fiddling, I'm convinced they are hooked up correctly. Same problem with speedometer. Likes to read 140 MPH, but fluctuates rapidly down into the 'teens. They both read zero when they should so I don't think the FB is the noise problem. I cranked the timers up to 150 and 250 where I noticed a vague improvement. Sample rates incompatible? Help...

    Oil pressure, water temp, volts, alt. light, check engine light, air temp all working nicely.

  9. #19
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    I would recommend a different value for your series resister (500 ohms) for your pressure instrument. The larger the series resister, the lower the voltage out but the more accurate you become until you reach the accuracy limits of the fusion brain. If you use a 51 ohm series resister, you will have massive errors. For the sake of argument, I will use units of percent. If you calibrate your readings to be correct at 0 percent and 100 percent then here is the actual vrs readout you will get:

    Actual Variable Value Displayed Variable Value
    100 100.00
    95 98.13
    90 96.14
    85 94.00
    80 91.71
    75 89.24
    70 86.58
    65 83.70
    60 80.57
    55 77.16
    50 73.44
    45 69.34
    40 64.83
    35 59.82
    30 54.23
    25 47.96
    20 40.87
    15 32.79
    10 23.50
    5 12.70
    0 0.00

  10. #20
    Constant Bitrate ACCLR8N's Avatar
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    That would give me a total output voltage range less than 0.75V at the bottom of the scale where all the noise is.
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