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Sweat monitor using electrodes.

Discussion in 'General Electronics Discussion' started by JPU, Sep 12, 2012.

  1. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Yes. (non-inverting)
     
  2. JPU

    JPU

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    May 19, 2012
    I'm just wondering, how feasible would it be to use a motion chip or accelerometer chip to achieve the elusive goal of measuring a horses pulse.

    Just
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Have you investigated placing an IR led/phototransistor clamp on the horse's ear?

    This is similar in theory to placing a clamp on a person's finger.

    Not being around horses much, I can't think of another location that is fairly thin and fleshy.
     
  4. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    There's not much point in having a differential amp for the second stage.

    Chris
     
  5. JPU

    JPU

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    May 19, 2012
    Thanks Steve.

    I have considered the ear method, however horses don't tolerate things about their ears which may lead to the device being "flicked" off.

    Chris, would you be willing to explain, via Tina how I can use a capacitor to eliminate noise. I have read up on bias voltages,,I think I get that!!!ish!

    Thanks

    Just
     
  6. JPU

    JPU

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    May 19, 2012
    Hi

    Please can you explain why the results from this circuit are not as expected. I would have expected output from the second op amp "VF2" to have been 20 X the output at VF1.

    I thought Id learned something, now I'm confused!

    Here is the tina file:

    http://dl.dropbox.com/u/7717360/diff opa and non invert opa.TSC

    Thanks JPU
     

    Attached Files:

  7. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Justin, I just wrote a 5 paragraph explanation but then deleted it in exchange for this.

    You're clipping!

    Chris
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    The resistors in the feedback loop of the second stage are way too small.

    I'm not sure that it will affect much in the simulation, but in real life you'll have a far higher power consumption that you might want.
     
  9. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Yes, I saw that also but it's not why he's not getting a voltage gain of 20 in his sim.

    Chris
     
  10. JPU

    JPU

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    May 19, 2012
    Chris

    The two words you used were more than enough.

    Now, I am being careless!

    I only used the resistors as I had tried every thing else I could think off and the last thing I did was quickly try two small resistors.

    Thanks
     
  11. JPU

    JPU

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    May 19, 2012
    Hi Chris

    I have added some more to the signal and introduced "Extra Noise" at 1k 70m.

    I am trying to achieve (purely to gain an understanding) a signal at V3 with extra noise on which will be equivalent to V3 with the extra noise off by using a high pass filter to eliminate the extra noise.

    I have tried to play around with what I think is a high pass filter to try and eliminate the 1k hz. However as usual I am not getting the results I expected. Should I use a low pass and a high pass filter together, should I give up?

    I have added V3 so that I can compare the results to V2 which has no filter.

    I have also included a second output with Extra noise turned off.


    Circuit:

    http://dl.dropbox.com/u/7717360/diff opa and non invert opa.TSC

    Hope you can help before going down the well tonight?

    Thanks

    Justin
     

    Attached Files:

    Last edited: Sep 28, 2012
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    VF1 looks like a nice swing of 2V peak to peak centred on 0V. So that's a gain of 10.

    Not sure why the output at VF2 is not symmetric though, or why the frequency doubling is happening.
     
  13. BobK

    BobK

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    VF2 is clipping. +-2V in, gain of 5 = +-10V out with a +- 5V supply, not going to work.

    Also, you want a low pass filter, not a high pass filter to cut out high frequency noise.

    Bob
     
  14. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    By this reply I thought you understood. You obviously don't.

    In the first circuit you were clipping, so your cure for that is to add more OpAmps, more VGs, more complexity?? WTF!? :rolleyes:

    Justin this is what I was going to post yesterday but snipped it because it sounded nasty. Sorry, but I can't avoid it and it must be said, though I have already told you this before, apparently not forcefully enough though. So here's the whole unvarnished truth...

    This science is not learned from the top down. If I explain why your not getting the results you expect you will not fully grasp it and tomorrow will be just be another question and the next day another. This is not a criticism it's just a statement of reality. Electronics is a science that must be studied from the ground up. By the time a student is studying OpAmps he or she knows and recognizes clipping when they see it. However, I would fully expect you to respond with "What's clipping?" but you didn't. You simply can not cut ahead of the line in this science.

    Justin, you have a DMM, new 100MHz digital scope, Tina Spice and electronic calculators. You have power in your hands that didn't exist and would have given me wet dreams when I was young. You also have a wealth of knowledge at your fingertips via the Internet. I didn't have this either. I've said it before but I'll say it again. Use our tutorial section, starting at the beginning with the Electron and work your way up.

    I was foolish to think I could tutor you through your projects. This could only work if you had the basic foundation to build upon. Throughout your threads you post a question, I answer, you veer off into left field. I'm burned out and dizzy from it all.

    This thread has triking similarities to another recent topic, where the OP found a valve schematic on the Internet and wanted to build it. There was nothing non typical about that but as the thread progressed he wanted to know how it worked. When myself and other members replied to a question his responses were just more questions about the answers he was given. You see, it's futile to tell someone that,... "You can't drive a speaker directly from that amplifier because valves are high impedance devices.", ...when the OP is going to respond with, ... "What's Impedance?".

    There are basically 5 categories of posters here.

    (1) The person who has no burning interest in electronics but wants to build a circuit to get a particular job done. They're not interested in the theory of operation, just getting it done.

    (2) Students and electronics enthusiasts that are 'progressively' educating themselves.

    (3) Includes members in category 1 and 2.

    (4) The members that assist 1, 2 and 3.

    (5) This is your category. You fit into category 3 but the term "progressively" is frustratingly absent.

    Before I hit the 'Submit Reply' button I want to reiterate that all of the aforementioned is not intended to demean you in any way. You have admirable and insatiable drive. You just need to structure and focus it. I'm just pleading with you to pour the foundation before you build the house! While you're pouring the concrete I'll be more than happy to help you do it in a structured way. :D

    Your friend,

    Chris
     
  15. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    I was hoping Justin would ascertain that on his own. As for the filter requirements, I'm not as sure as you are. The human body picks up copious amounts of mains frequency hum. Maybe a notch filter would be apropos?

    Chris
     
  16. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    That doesn't surprise me at all. It's far easier to generate harmonics from a distorted signal or when mixing a signal or signals that are distorted prior to being mixed.

    Chris
     
  17. BobK

    BobK

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    Agree. I was only referring to the test circuit he was using. The noise was higher frequency than the signal in that case, though only by 2X so it would have to be a sharp cutoff filter to do much.

    Bob
     
  18. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Oh, I see what you're saying. I was so frustrated from all the bouncing around that I hadn't read Justin's post completely. ;). I don't imagine that the Oxicodone and Roboxin is making me any sharper either. Last week I would have begged someone to shoot the Elephant on my shoulders. I'm nearing the point of just having someone shoot me!:eek:

    Chris
     
  19. JPU

    JPU

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    May 19, 2012
    Hi

    I did get the "clipping" bit, the 5V+ 5V- in, the operational levels of the OPA134, but that is not my problem!

    Sorry, I was in a rush to get off to work this morning and I didn't put my thoughts over as intended/clearly as I would have liked. My fault!

    Thanks

    Justin
     
    Last edited: Sep 29, 2012
  20. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    I'm not sure what "FM" is. Frequency Modulation? Maybe a better question would be,,Do I really want to know?

    Anyway, Based on the 5V supply rails, minus about a volt and knowing your total expected gain, calculate what VG output levels you need to eliminate the clipping.

    Chris
     
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