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  1. #1
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    Interfacing a Basic ASI Gauge

    Hello everyone,

    I have managed to pick up today 7 real-world aircraft instruments for an outstanding price.

    One of the items picked up was an altimeter. It is an altimeter ranging from 0-450, presumed ex-military.

    Anyway, I was wondering how this could be interfaced. Maybe through using the USBServos Card from Opencockpits? I'm getting the hang of SIOC (having just sucessfully implemented the USBKeys Card) but am pretty much lost on how to get the "output information" from the SIm to reference in SIOC, and then from then on onto the actual servo motor.

    Even then, how do I define how mcuh the motor turns? Obviously,different gauges have different scales, so how do I tell the USBServos Motor this?

    Maybe someone how has interfaced something like an analogue ASI could give me some tips.

    Thanks very much,

    Jack

  2. #2
    500+ This must be a daytime job 737NUT's Avatar
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    Re: Interfacing a Basic ASI Gauge

    It is kind of a complicated process but once you get the hang of it, it is easy. First off you need to determine what drives the gauge. A dc motor with a pot as feedback, (easy to interface) Synchro resolver's and transmitters, or simple air pressure or differential air. If you have to add a servo to drive a gauge, they are limited to 180deg movement. So if you have a gauge that has more than that, which 99% do, you will need to add some kind of gearing. Again, easy once you get the hang of it. You could even drive an altimeter with a simple dc motor and 10turn pot. Using gearing and programming. Once you have the mechanical set-up done, you test it by using IOCP console and commanding the servo to position 1-1022 to determine the range that matches your gauge. Example, my VSI gauge -5000 = servo position 450 and +5000 = servo position 925 Once you know that, you apply a little math and a small program in sioc and it functions perfect! Here is an example of some of my gauge scripts,

    Var 0001, name VSI, Link USB_SERVOS, Output 1, PosL 170, PosC 612, PosR 1023, Type 1 // vsiservo

    Var 0002, name EngN1servo, Link USB_SERVOS, Output 2, PosL 345, PosC 647, PosR 950, Type 1 // N1 Servo

    Var 0003, name egt1servo, Link USB_SERVOS, Output 3, PosL 1, PosC 550, PosR 1023, Type 1 // EGT Gauge

    Var 0004, name eng3N2servo, Link USB_SERVOS, Output 4, PosL 345, PosC 647, PosR 950, Type 1

    Var 0005, name Eng3N1servo, Link USB_SERVOS, Output 5, PosL 345, PosC 647, PosR 950, Type 1

    Var 0006, name Eng2N2servo, Link USB_SERVOS, Output 6, PosL 345, PosC 647, PosR 950, Type 1

    Var 0007, name eng3N2, Link FSUIPC_INOUT, Offset $09C6, Length 2 // N2 rpm for eng 3
    {
    L0 = &eng3N2 * 0.00606
    L1 = L0 * 5.5
    L2 = 345 + L1
    &eng3N2servo = L2
    }

    Var 0011, name eng1N1, Link FSUIPC_IN, Offset $0898, Length 2
    {
    L0 = &eng1N1 * 0.00606
    L1 = L0 * 5.5
    L2 = 345 + L1
    &EngN1servo = L2
    CALL &ConfigWarn1
    }

    Var 0012, name Eng1Egt, Link FSUIPC_IN, Offset $08BE, Length 2 // Eng 1 EGT
    {
    L0 = &Eng1Egt * 0.05249023 // 16384=860C
    L1 = L0 * 0.522727
    L2 = L1 + 335
    &egt1servo = L2
    }

    Var 0013, name relay1, Link USB_RELAYS, Output 1 // AP Power

    Var 0014, name APMaster, Link FSUIPC_INOUT, Offset $0278, Length 2 // Status of AP master switch
    {
    IF &APMaster = 1
    {
    &relay1 = 1
    }
    ELSE
    {
    &relay1 = 0
    }
    }

    Var 0015, name Eng1N2, Link FSUIPC_INOUT, Offset $0896, Length 2
    {
    L0 = &Eng1N2 * 0.00606
    L1 = L0 * 5.5
    L2 = 345 + L1
    &Eng2N2servo = L2
    }

    Var 0016, name No2N1, Link FSUIPC_INOUT, Offset $0930, Length 2
    {
    L0 = &No2N1 * 0.00606
    L1 = L0 * 5.5
    L2 = 345 + L1
    }

    Var 0017, name eng3N1, Link FSUIPC_INOUT, Offset $09C8, Length 2
    {
    L0 = &eng3N1 * 0.00606
    L1 = L0 * 5.5
    L2 = 345 + L1
    &Eng3N1servo = L2

  3. #3
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    Re: Interfacing a Basic ASI Gauge

    Okay that's fanastic. So for an ASI gauge that runs through about 500 degrees, I would use a pot with a mechenical mechanism? Would I use the USBServos to interface?

    Thanks,

    Jack

  4. #4
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    Re: Interfacing a Basic ASI Gauge

    The gauge runs off differential air pressures. "Sucking" on the input increase the ASI, whilst "Blowing" on the input decreases the speed. Can this be interfaced?

  5. #5
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    Re: Interfacing a Basic ASI Gauge

    Right, I'm a little bit confused here. The gauge works off air pressures, can this still be interfaced?

    Also ,does anyone have a circuit diagram for something like an ASI that moves about 500 degrees?

    Thanks,

    Jack

  6. #6
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    Re: Interfacing a Basic ASI Gauge

    Okay, I think I need to sort out the mechanical system first.

    As I said, the gauge works off've ir pressures. If needs be, could I scrap this system and simply attacth a DC Motor with a Pot, and interface it that way?

    Are there any circuit diagrams available for anything like this?

    I think I can figure out the programming side of things later, I just need to know the actual mechanical connections between the USBServos Card and my Air-Pressured ASI Gauge, which moves through 500 degrees of movement.

    Thanks alot,

    Jack

  7. #7
    500+ This must be a daytime job 737NUT's Avatar
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    Re: Interfacing a Basic ASI Gauge

    Take out the air diaphram and associated parts. By using some gearing, you turn the shaft witha servoor a dc motor Servocity.com as all the stuff you need.

  8. #8
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    Re: Interfacing a Basic ASI Gauge

    Hi there,

    Yes I'm taking out the air diaphram, it is a very strange system which cannot be interfaced in any way. I will just connect the needle to a servo. Also, what's interesting is the fact that there is a "U/C" flap which pops up and down when connected to a 5V power supply.

    Anyway, lets say I purchased the USBServos Card. What else will I need to purchase? What will I need to buy from Servocity.com? What else should I know?

    Also, will connecting a Servo and DC Motor direct to the Card work? I thought you mentioned something about limited 180 degree movement, etc.

    Thanks very much,

    Jack =)

  9. #9
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    Re: Interfacing a Basic ASI Gauge

    Okay, I think as I'm understanding this more and more I've boiled it down to some important questions...

    - What EXACTLY do I connect to the USBServos Card, and, what attatched to what, etc?

    - What motor/servo do I need to connect? There are thousands on Servocity, which one(s)?

    Thanks,

    Jack

  10. #10
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    Re: Interfacing a Basic ASI Gauge

    Jack

    You need a servo not a motor.
    You will need a servo that can either fit in the housing or easily be mounted to it, probably something like a Hitec HS-55
    Check the full scale deflection of the needle against the servo movement range, it is likely that you will need to use gearing
    Read the OC USBservos card manual as to how to hook up the servo, do not just plug it in as it is very likely that you will need to change over the servo leads and if you do not do this then it will blow up
    Preferably only try the servo out by using a sioc programme first, else be very careful that the servo does not move under power to the full extent of its range as it could easily stall and burn out if it is not getting a position signal

    David

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