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Sweat monitor using electrodes.

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

  1. JPU

    JPU

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    1
    May 19, 2012
    Chris

    I have used the view - separate curves option. I can split the curves up to see vf1, noise1 and vsig but there is no noise2?

    Justin
     
  2. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    You're still not getting the point of this exercise. At this point you shouldn't see Noise2 because it's set to OFF in its properties. The purpose of this simulation is to show how unwanted noise can modulate a wanted signal that we're amplifying. Before we move on do you understand this?

    Chris
     
  3. JPU

    JPU

    281
    1
    May 19, 2012
    Chris

    I think I get it. I did post a message with my interpretation. I was unsure how to get the wave to show. I have now.

    I'm ready for the next bit.

    Thanks

    Just
     
  4. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    OK, "next bit". Since you now have Vnoise2 turned on, what does your signal to noise ratio look like on the OpAmp's (VF1) Output? In other words, do you see any noise there?

    Chris
     
  5. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Justin, I forgot to mention that my wife and I are having a few drinks and dinner with my buddy Ron today. When I first started contracting at the hospital Ron was the Bio-Med Electronics supervisor. I will be picking his brain regarding ECG's/EKG's. I do know that our EKG's were tested and calibrated by Bio-Med using a simulator that mimics the human body's electrical impulses and presumably noise.

    Chris
     
  6. JPU

    JPU

    281
    1
    May 19, 2012
    Hi Chris

    I have taken a look at the new output when I switch on the noise2. The results, I don't quite understand.

    I would have thought that as the two noise waves are of the same type then they would combine together (constructive interference) to create a larger wave which would be the sum of the two waves combined. However, from the results VF1, seams to be unaffected now by the noise??

    Please can you explain..

    Great news regarding your friend from Bio-Med, I'm sure he will have a wealth of knowledge..

    I have read most of the information on this site,http://www.acoustics.salford.ac.uk/feschools/waves/super.htm

    I read through it last night, very interesting. That's where I found the phrase, constructive interference.

    Thanks

    Justin
     
    Last edited: Sep 25, 2012
  7. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Yes, we've finally arrived at the purpose of this exercise. OpAmps have two inputs. Inverting and Non-Inverting, which is why they're differential amplifiers. Your noise generators are hooked up in Differential Mode. If two input signals, noise in our case, are of the same amplitude, frequency and phase the OpAmp will attempt to amplify both. However, since the Inverting and Non-Inverting inputs produce an output 180° out of phase with each other the noise output will be canceled. Think of it this way. .. What's the sum of +1V and -1V?

    Do you see the connection between this exercise In regards to the heart beat signal and mains noise found on the body? My guess is that some of the multiple electrode leads that you see on an EKG are used as intentional noise inputs. I will verify this today.

    Did you know that the differential characteristic of OpAmps make them suitable to perform simple math? Assume an OpAmp with a gain of (1) unity. If we apply +2VDC to each input the output will be zero . If we increase the Non-Inverting (+) input to +3VDC the output will be ((-2) + (+3) = +1V. Conversely, if we had increased the Inverting (-) input to +3VDC the output will be ((+2) + (-3)) -1VDC.

    You can sim this in Tina. If you do I would recommend using Interactive Mode. First save your current .TSC. under a different name, replace all the voltage generators with two batteries and click the DC button on the tool bar.

    Chris
     
  8. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
  9. JPU

    JPU

    281
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    May 19, 2012
    Chris

    I get it. Is that why ECG machines have three electrodes. 2 grounds(1 ground being placed away from the heart so as to have no signal from the heart) and a signal. The 2 grounds are fed into the non inverting and inverting side of the amp. The signal will be only sent in one side.

    I understand the concept of the noise being cancelled out now I think.

    So we don't need caps at all ????:confused:

    Where now?

    Justin.
     
  10. JPU

    JPU

    281
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    May 19, 2012
    Chris

    I have just seen your post,, I have emailed Plessey. That unit looks exactly like what I need. However, I do think that we are not that far off building our own pulse counter, would you agree???

    Justin
     
  11. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Unfortunately I can't confirm that EKGs work as you describe, only that OpAmps can be operated as I described. Whether any of the EKG leads are actually earth ground, circuit ground or ground at all, I don't know. For certain, when connected to the body, things get extremely messy. One thing I can be certain of is that filtering will still be quite necessary. How any of this relates to the Plessey module is unknown because I haven't read the details.

    Chris
     
  12. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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  13. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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  14. JPU

    JPU

    281
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    May 19, 2012
    Hi Chris

    I emailed Plessey last night and got a reply today. They sent me some PDFs regarding their products. They also supplied a contact name and mobile number which I phoned immediately (impulsive as ever) and I spoke to a chap for about 45 minutes. Very interesting!

    He has also sent me some literature which I will read later which includes a break down on costs. I am not sure if the sensors are what I need or if they can do much more than what we are already trying to build. There seams to be a need for software to interpret the signal from the sensor and for this I would need to incorporate their chips into the overall design. If your interested then PM me your email address and I will forward the email to you.

    If you have the time and patience can you continue with your demonstrations as I would very interested to know how the capacitor can be used to also filter noise and how we chose the correct capacitor to filter specific noise.

    In the meantime, do you think it is worth me trying to build a differential circuit with the OPAs I have bought.

    Regards

    Justin
     
  15. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Justin, I just emailed my niece, who's been raising horses since she was knee high to a grasshopper. If there is any way possible to duplicate the finger tip Optocoupler concept on a horse, I want to know about it. It would solve the noise issue.

    Yes, I'll continue to tutor you. We'll talk passive and active filters next.
    Chris
     
  16. JPU

    JPU

    281
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    May 19, 2012
    Hi Chris

    Thanks for your help as always. I am ready for the next step!

    Would you also be so kind asto explain what this means please :-

    " I would probably start with an inverting gain of about 100 in the first stage, with output biassed at about Vcc/2 and a gain of 20 - 50 in the second stage, possibly with the output biassed a few hundred mV above ground."

    This is a section of a post by Allycat in the picaxe forum. Its in response to my question regarding counting pulses using a picaxe for which I provided the link earlier. Here it is again:
    http://www.picaxeforum.co.uk/showthread.php?22185-ADC-electric-input-pulse-counter-help-please/page4

    I don't understand what he means by the words I have converted to italics and red! Unfortunately for me the guys in the picaxe forum are not aware of my limited understanding of electronics and phrases.

    Cheers

    Justin
     
  17. BobK

    BobK

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    Jan 5, 2010
    Horses got fingers? I knew chickens do, becuase they are tasty when deep fried, but horses?

    bob
     
  18. JPU

    JPU

    281
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    May 19, 2012
    Hi Bob

    I think your knowledge of horses is as broad as mine is of electronics! ;)

    Seriously though, I did consider using the optocoupler Chris mentions. I thought about putting it on the horses ear. It's ears have a good blood supply and are thin. However horses in general hate anything messing with their ears and the attachment of a sensor is likely to make his heart rate race!

    I am starting to realise why at present there is no cheep and simple method of measuring a horses heart rate electronically.

    JPU
     
  19. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    So I guess attaching the sensor the genitalia is out too?:rolleyes:

    FYI, paleontologists believe horses once had toes.

    Chris
     
  20. JPU

    JPU

    281
    1
    May 19, 2012
    Hi Chris

    I had a go last night of building the differential op amp. My aim was to have two connected and to use a gain of 100 in the first and 20 in the second. However I immediately (well, 1hr into the build) came across a problem. I have 2 inputs into the initial amp,,,but then only one output. The second differential amp requires 2 inputs again, so where do I get the second input for the second amp????

    I studied some websites but it all got a bit confusing...

    At first I thought I had bitten off more than I can chew with this project,,now I know I have!!


    Would it be feasible to use a differential for the first stage followed by a none inverting for the second??

    please, help

    Justin
     
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