Winscope, my PC, and 12V?

Discussion in 'Electronics Resources' started by pntrbl, Aug 2, 2008.

  1. pntrbl

    Thread Starter Active Member

    Apr 21, 2008
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    Not owning an oscilloscope and needing to check out the hall-effect switching on my anemometer project, I'm looking at some freeware called Winscope for a possible solution. Obviously this is not a "real" oscilloscope. It uses the sound card on a PC to produce a visible waveform, but that should be good enough to set hall-effect proximity I would think.

    I'm also hoping I can use it for calibration. With a borrowed anemometer I should be able to get a frequency for a given windspeed.

    Reading thru the help section on the Winscope freeware I see a precaution that sound card inputs are typically not more than 2VAC. Since I'm planning on running an AH175 hall-effect on 12V it's a good thing I ran into that! :eek:

    My sound card is an ADI 198x and I've googled myself silly looking for some info on something besides drivers .... but no joy. Probably not a good idea to put 12v in there anyway .... :rolleyes:

    So that's where I'm at. Any thoughts, help, advice, etc. are always welcome ...

    SP
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    You must make a voltage divider at the input of your Winscope to reduce the level to less than 2V. The voltage divider will be very inaccurate if you don't calculate the values for the voltage divider including the input impedance of the sound card. Maybe you don't know what is the input impedance.

    A line level input has a max of 2V. A microphone input might have a max allowed input voltage that is much less than 2V and might have a low input impedance.

    The sound card has an AC input so DC levels will not be seen like on a real 'scope.
     
  3. pntrbl

    Thread Starter Active Member

    Apr 21, 2008
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    You called that one right Guru. I haven't got a clue!:D

    Thank you for pointing out I'll need to consider the impedance tho. I guess I knew DC resistance alone wasn't the answer, but the words input impedance didn't float up from the recesses of my mind until you mentioned them.

    SP
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    I'm working on a project to use WinScope, it's posted in the projects forum. When I get it done I'll run some tests and post the results.
     
  5. pntrbl

    Thread Starter Active Member

    Apr 21, 2008
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    Thanx for the info Bill. From your opening post I got the link to AAC's Vol.6 PC Oscope chapter where I found some encouragement. Frequency precision was noted as being surprisingly good so my hopes of using WinScope for calibration are looking up. :)

    Would a step down Xfmr be a crazy idea? Could I de-couple with a cap to get 12VAC switching back and forth in the primary from the DC out of the hall-effect? After a 10-1 step down I'd see a 1.2VAC out.

    Who knows? :D Not me!

    SP
     
  6. pntrbl

    Thread Starter Active Member

    Apr 21, 2008
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  7. SgtWookie

    Expert

    Jul 17, 2007
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    Here ya go ;) Have a look at the attached.

    V1, R3, and Q1 are a rough simulation of your Hall-effect sensor. Q1 is the open-collector output transistor thingie we'd kicked around before.

    R1 is the pull-up resistor I'd previously mentioned that you'd need to use to get an output from the sensor.

    D1 is a new twist - it's used to clamp the maximum output voltage to the Vf of the diode. The type of diode to use doesn't matter a lot. You could use a 1N4001 through 1N4007, a 1N4148, a 1N941, and many other silicon diodes. The whole point of using a diode there is that when it's forward-biased at low current, it'll drop less than a volt across it. This will keep it at a level safe enough for your sound card.

    From there, just connect it to a stereo mini plug.

    You don't really care about the amplitude - you already know that's going to vary between 12v and some low voltage when the output transistor is conducting. This is just clipping it to a safe level so you can see what the frequency of your output signal is.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    Oh, and you really don't want to try using a transformer. The output of the Hall-effect sensor may switch on and off quite quickly. The inductance of the transformer could cause very high peak voltages due to the reverse EMF when the magnetic field starts collapsing.
     
  9. pntrbl

    Thread Starter Active Member

    Apr 21, 2008
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    Elegantly simple once again Sarge and what's even more surprising is ... I understand it!

    Lest you guys think I'm not using all of the information and knowledge you so kindly provide me, here's some pics of the GM pointy thing shafted up with miniature Class 5 bearings.

    [​IMG]

    [​IMG]

    Somehow my son-in-law can carefully pinch that little Class 5 between his fingers, and without any rubbing, blow on the pointy. Ya oughta see it spin! :)

    SP
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    Pretty spiffy - what are you going to hold those bearings with?
     
  11. pntrbl

    Thread Starter Active Member

    Apr 21, 2008
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    An Alu housing/body is next. It's currently hiding in a 3" cylinder, but I'll find it. ;)

    SP
     
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