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  1. #1
    25+ Posting Member hca's Avatar
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    Question Synchro transmitter circuit

    Anyone using original 400hz sychro instruments?

    I have hunted about the net without luck for a synchro transmitter circuit suitable to drive gyro or adf and other instruments.

    Is there a cheap way out here, maybe one of the sim companies have a solution but I have not seen one yet.

    Or has any one got a circuit of an ADF or similar which provides the signals?

    Its a pity to replace the syncros with steppers for the sake of some electronics.

  2. #2
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    You can drive synchro instruments with a commercial digital-to-synchro converter module, or with a synchro transmitter connected to servo.

    There have been a few who have made digital-to-synchro circuitry. A general approach is to use a sample of the 400 Hz power as input to two channels. One channel scales by the sine of the synchro angle. The second channel scales by -sine of (the synchro angle + 120). The scale function can be done with a multiplying DAC or a digital potentiometer. The MDAC approach offers more resolution. Both channels will need power amplifiers, but many audio power amp chips can do this.

    There will be just such a circuit in an upcoming book. I'd like to say that the book's coming out "real soon", but sadly my ability forecast completion dates must rank among the worst in the industry, so I'll meerly alude by saying it's closer than it's ever been.

    A picture of the project is here http://www.mikesflightdeck.com/upcoming_book.htm about halfway down under "Using Real Instruments".

  3. #3
    25+ Posting Member hca's Avatar
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    Thanks Mike,

    Its a waste to modify working indicators when its avoidable, and I figure its as easy to drive a synchro as a stepper, at least the software side.

    I was looking at a Max532 from Maxim for an mdac, partly because its easy to order from Bali but also its driven from SPI which suits my pic based approach to controlling the sim.

    Out of interest what Audio chip did you used as a driver? Here the electronic shops are full of Sanken hybrids and small stero audio modules for the price of a box of smokes.

    As I don't have much here at home in the way of test gear, I am trying to skip the R&D stage. Also no point reinventing the wheel and its good to use bits any one else can obtain to copy the design.


    Good luck with your book, that's quite an undertaking!

    Cheers Harry

  4. #4
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    I used an LM1875 audio amp. IIRC the version built by ST went for about a dollar. The Maxim MDAC should do the trick. I worked with them initially but prices were going up and availability of through-hole versions was dropping. I switched to an LTC1590.

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