Circuit Design help needed

Discussion in 'Homebrew and Kit Projects' started by EI2GLB, Jul 31, 2019.

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  1. EI2GLB

    EI2GLB Ham Member QRZ Page

  2. SM0AOM

    SM0AOM Ham Member QRZ Page

    Yes, it is very "doable".

    I would suggest a differential or summing DC amplifier feeding an "off-the-shelf" Digital Voltmeter Module.

    The gain factor would have to be chosen from what maximum deflection the chosen sensor has and its scale factor.

    If you only intend to measure the angle in one quadrant, 0 - +90 degrees, then a sensor with a scale factor of 50 mV/degree fed into a summing amplifier with a gain of 0.02 where an offset voltage of -5 V is added to balance the sensor null offset would provide the desired result.

    This gives an output of 0 to 0.09 V for 0 to 90 degrees, and if the full scale of the DVM is chosen to be 90.0 mV
    the number of degrees can be read directly.

    A better solution with respect to temperature stability
    is however to use a larger DVM full scale with a corresponding higher gain in the summing amplifier, and shift the decimal point to show the correct value.

    73/
    Karl-Arne
    SM0AOM
     
    KB0MNM, AC0OB and WA7PRC like this.
  3. EI2GLB

    EI2GLB Ham Member QRZ Page

    Thank you for the reply, I will do some research and see how to achieve all that you mention,

    73
    Trevor
    EI2GLB
     
  4. VK4HAT

    VK4HAT Ham Member QRZ Page

    The sensor outputs a voltage. You can sample that voltage with the ADC on a cheap micro controller with you can also use to drive the LED/LCD display. Code wise its rather trivial to do.
     
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  5. AF7XT

    AF7XT Ham Member QRZ Page

    Karl-Arne will do that to you , often , like on a regular basis ...

    ;)
     
  6. VK2TIL

    VK2TIL Ham Member QRZ Page

    There are other sensors that present a similar problem of scaling and offset; the AD8307 RF power sensor is one such. Whilst the "numbers" are different, the principle may be understood by studying the solutions reached by different designers.

    The schematic and an explanation of one design, by Lou VK3AQZ, is here;

    http://vk3aqzkits.com/wp-content/uploads/2018/08/VK3AQZ-RFPM1-power-meter-kit-V1.pdf

    Bob Kopski K3NHI was probably the first to publish a similar design, in QEX for May/June 2002; it doesn't seem to be available for download but perhaps you can find QEX through a library.

    I built an audio voltmeter using the AD636 log-amp, with both digital and analogue meters, that required similar signal processing; here are the schematics;

    https://i.postimg.cc/8CfM5XHx/Circuit-Diagram-1.jpg

    https://i.postimg.cc/Wb4DzfpS/Circuit-Diagram-2.jpg

    One "trick" to home-made instruments is to incorporate a lot of "adjustability".

    If you study op-amp design (there are lots of papers available, particularly from Texas Instruments) and designs like these you will see how scaling and offsetting can be done.

    .
     
    KB0MNM likes this.
  7. WA9SVD

    WA9SVD Ham Member QRZ Page

    Me thinks the OP is WAY over his head. This is NOT a site to ask members to design s0methinhg FOR:(:mad: him, much less make it at least half "idiot proof." After all, there are so many ways fools can exist, and we can't count them all:(:rolleyes:.
     
  8. AF7XT

    AF7XT Ham Member QRZ Page

    Not when he's asking the right questions.

    Well in a word , no , no it isn't but it is the right place to ask.

    A modicum of "suicide prevention" is usually sufficient.

    Pontificate less , experiment more. ;)
     
    NQ1B and N2EY like this.
  9. WA9SVD

    WA9SVD Ham Member QRZ Page



    I experimentation PLENTY. What YOU see as "pontification" is just common sense to many of us. If someone can't simply read a PDF file with a spec sheet, perhaps they are FAR in over their head, and should NOT try to modify a published circuit.
    There was NO "pontification," real or implied at THIS end, but (misunderstand,) it may be on your end, You have my sympathy, in which case, YMMV.
     
  10. AG5WC

    AG5WC Ham Member QRZ Page

    I can count at least one.
     

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