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Sweat monitor using electrodes.

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

  1. JPU

    JPU

    281
    1
    May 19, 2012
    Hi all

    I have an idea. I would like to build a device that monitors a horses state of health. The device will use a small electrode to measure if a horse is sweating. I don't need to know how much he is sweating just is he or isn't he.

    My idea was to create a simple circuit that would power an electrode. If the horse is sweating then the supply will flow across the sweat (damp skin) to the receiving electrode. This voltage would then be measured using a picaxe. If he readadc is above a certain level then a LED lights.

    I have been told this circuit will result in damage to the electrodes over time. I was also wondering, won't this circuit also consume a lot of battery power?

    My questions are

    Is there an easy and more efficient way todo this.

    How could I improve the reliability of such a device.

    How could I increase or decrease the sensitivity.

    Thanks for reading and any help you might give.

    JPU

    Ps I'll upload schematics and code in the morning. I cant do it on an iPad!!!!!
     
  2. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    An Ohmmeter will work. You just need some kind of sticky pads that will stick to a hairy horse. I wouldn't worry about electrolysis at these very low currents. ;)

    Chris
     
  3. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    If the object is to light an LED then nix the picaxe. Use low-power opamps to conserve battery power. I would not try to put more than a few tens of microamps through the horse. Corrosion of the electrodes will depend upon the material used. Gold would be good. Doesn't a horse have hair over its skin? Will you need contact with the skin, or will wet hair be conductive? My first thought was to use gold-filled military insignia for a 2nd lieutenant (butter bars) as flat paddle contacts, but not appropriate if you need pins to get through the hair.
     
  4. JPU

    JPU

    281
    1
    May 19, 2012
    Hi Chris

    I know what an ohmmeter is and does, but I have no idea how to build one or how it works. I have included my schematic and code and I wonder is this fundamentally an Ohmmeter?

    Hi Laplace

    Sorry I have not provided all the facts. I intend to link this sweat monitor, a heart rate monitor and a respiration monitor to a Picaxe controlling circuit that will then send the data serially via my EMF boards to a LCD display.

    So Chris, did you just sit back in your chair , roll your eyes and think "I am out of here!", I hope not, as I would really appreciated your expert help on this one.:eek:


    Code:
    	symbol ADCval = b5			
    	symbol    Vin = w3   	
    	B9=0 B10=0 B11=0
    
    
       #com 6									
       #picaxe 08M2						
       #terminal 2400					
    
    ' =================== Begin Main Program ====================
    
    do
    	
    												
    	readadc c.1,ADCval					
    
    	IF ADCVAL>100 then low c.2: end if
    	
    	
    	IF ADCVAL<90 THEN high c.2:end if
    	
    		
    	Vin = ADCval * 100 / 51		
    
    
    
    	bintoascii Vin,b4, b3, b2, b1, b0	
    	;sertxd (b2,".", b1, b0," volts",cr,lf)
    	
    	
    	serout c.0,n2400,(254,1)
    	serout c.0,n2400,(254,128) 
    	serout c.0,n2400,(b4,b3,b2,".", b1, b0," volts")
    	serout c.0,n2400,(254,192)
    	serout c.0,n2400,(#ADCval, " adc val")
    	
    	
    			
    loop
    
    Regards

    JPU
     

    Attached Files:

  5. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
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    May 8, 2012
    Ah, you love your Picaxe, don't you? At a glance it all looks OK but you may have to play with the value of R2. My guess is that it will need to by higher. You can do preliminary tests on yourself.

    Chris
     
  6. JPU

    JPU

    281
    1
    May 19, 2012
    Chris

    Love it? its taken over my life!!

    I'm going to take over the world with Picaxe!!:D

    Do you think I will have many problems using this type of setup .ie corrosion of the electrodes?

    Also, how would I work out how much power this setup would consume. Not the Picaxe, but the sensor?

    Also,,,,,,,

    I built a heart rate monitor the other day following another thread I started. The unit works from an infra red led. The light is bounced back from the capillaries onto a photocell. The voltage is sent through an op amp and the result is a flashing LED in time with your heart beat. It works well, however, not so good on furry horses!!! Someone mentioned using a ceramic microphone instead. Do you think Chris it would be possible to detect a heart beat and then filter the beat from all other noise so as to count the beats per minute or is this going to be way beyond my scope?:p

    Regards

    Justin
     
  7. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    648
    May 8, 2012
    Justin, your wife must LOATH me. :rolleyes:

    Even if the Horse's skin resistance is 0 Ohms, which won't happen, the max the contacts could pass is 500uA with R2 = 10K. (5V/10K= 500uA)

    Regarding the contact pads: Something gold plated would be best. The pad current is going to be a very minor factor as far electrolysis is concerned because the current will be very low. Corrosion from salty sweat will be more prevalent. Wipe them down with a damp cloth after each use.

    Heart rate: IMHO the best way to make an acoustic pickup is to start with a stethoscope design that couples to the Mic.

    Chris
     
  8. JPU

    JPU

    281
    1
    May 19, 2012
    Chris

    If I can ever afford to buy her a BMW she will love you then!!

    How complex would you guess the electronic circuit would be to listen to the heart using a stethoscope design, isolate the beat from back ground noise and then count the beats. :confused:

    I suppose I am really asking "do you think I would be way out of my depth"?:eek:
    JPU
     
  9. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    648
    May 8, 2012
    Stethoscope to Mic pickup - Mic pickup to OpAmp - OpAmp to Picaxe ADC - Program to LCD.


    Not from what you've demonstrated thus far but sooner or later you will be needing a Scope. This project in particular would certainly benefit by having one. Don't tell the wife I said this but get the scope and have her wait on the BMW. :D

    Chris
     
  10. JPU

    JPU

    281
    1
    May 19, 2012
    Brilliant! I have always wanted an excuse to buy one. :D

    However, Why? This is a serious question, what does a scope do and how could it help?

    Would I need one with specific features?:confused:

    Which type would I need, 10Mhz 20mhz etc. I have had a look on ebay and at maplin.co.uk These babies aren't cheap..


    Thanks.

    JPU
     
    Last edited: Sep 13, 2012
  11. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    648
    May 8, 2012
    A scope has multiple functions but it's primarily used to plot voltage vs time. It can see things that a multimeter can't. A scope is the most valuable instrument found on any test bench. When hospital staff are looking at a heart monitor they're actually looking at a scope that's dedicated and tailored just for this purpose.

    Which scope to buy will be dependent upon how deep your pockets are. Generally speaking, the higher the bandwidth the higher the price. There are also USB based scopes that use your PC as the display. Many people feel that when the cost differential between a decent scope and a USB of equal bandwidth converge the USB isn't worth the cost when you can have a real scope for near that price.

    I've not kept current with today's very large scope market. My head is still in Tektronix land when no lab was considered to be one without them.

    I invite opinions from other members that have kept current.

    Chris
     
  12. JPU

    JPU

    281
    1
    May 19, 2012
    Chris

    Thanks for your reply. I have read a little about scopes today and I feel that I will have to make a purchase to even understand what they can do. After all just "having a go" is sometimes the best way to learn!:p

    Please can you take a look at the circuit I have attached. I haven't taken a monumental leap forward in my abilities but I am afraid I have to admit I ripped this design from another chap who placed it on a blog entitled Heart rate measurement from fingertip. http://www.embedded-lab.com/blog/?p=1671

    The circuit is easy enough to build but it took me about 5 days to get the led to flash to a heart beat as I needed to use a 68ohm resistor in place of 150ohm that he uses and then a 470ohm pot in series (as he states!). The light flashes when the 470 pot is set to 69ohms and only 69!!!

    Anyway, as you can see, I have added a small Miniature Piezo Transducer which I purchased from the picaxe store. The LED lights even at the very slightest sound or very smallest pulse of air, but as I mentioned earlier, how do I separate the noise from the signal????:confused:

    I have to confess I feel as though I have now become an international nag and I am worried that my constant questioning and attempts to steel from you, your hard earned knowledge may be beginning to annoy you. Please feel free to tell me to take flight if I am becoming a pain in the ar*e!

    If however you don't mind, then Chris,,,where the heck do I go from here with this circuit or am I going up the wrong path?

    Thanks, respectfully

    Justin
     

    Attached Files:

    Last edited: Sep 14, 2012
  13. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Justin before I comment on your circuit I'd like to read the original article but the link to the fingertip heart rate monitor is broken. Please post it again.

    Oh... No one has to guess when I'm annoyed. I'm the most overt guy you'll ever meet. :p

    Thanks,
    Chris
     
  14. JPU

    JPU

    281
    1
    May 19, 2012
    Chris

    I don't know what appended there. I have now edited the post and added the link manually.

    Here is the link and another which is more detailed:

    http://embedded-lab.com/blog/?p=1671

    http://embedded-lab.com/blog/?p=5508

    If you can help with this one do you think I should start a new thread Or revert back to the existing heart rate thread i started as this thread is now unrelated to its title. What are our thoughts?

    Regards

    Justin
     
    Last edited: Sep 14, 2012
  15. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Perhaps the forum Gods can split this thread where it switches tracks and give this siding a new title.

    I read through the information in both links.

    http://shine.yahoo.com/parenting/pb-38-j-worst-weapon-kid-bring-school-215000284.html

    They're both quite informative and thorough. The only thing that hung me up was where point "a" on the amplifier schematic in the above link is supposed to go. It's the Cathode of the Pulse LED. I would think it would be grounded but it doesn't indicate that.

    I don't see how this circuit relates to your audio pickup approach which isn't the proper way to measure pulse rate.

    So this begs the question... Where is the index finger located on a Horse? :p

    Chris
     
  16. JPU

    JPU

    281
    1
    May 19, 2012
    Chris


    Thanks for this link, but its Peanuts??LOL!

    At last I have an answer for you! :cool:It goes back over to the left of the schematic just below D1. I think its so that the pic can switch off the circuit?

    Ha ha thats the problem, they don't have toes!;)

    No, this circuit isn't designed for audio pick up. However, I have given this issue some thought and there are a number of problems associated with measuring the horses heart beat especially for the application I have in mind.

    I wish to create a device that the lay person can use. ie the average horse owner. I want them to be able to strap the device around the girth of the horse and connection or sensors need to be inbedded into the girth strap itself.

    Problems-

    1. Horses are hairy and I don't want the user to have to shave any area of the horse.
    2. There are a large number of intestinal sounds which will make acoustic pick up difficult.
    3. Horses have no fingers and will not tolerate clips or sensors on their ears.
    4. The device is to be used to measure a horses health e.g during an episode of colic during which time the animal may lay down. So the device must be robust and have a sensor that can tolerate movement.

    There are ECG machines on the market available for horses ( I have spoken to a vet today) however they use crocodile clips to pinch the skin around the heart area.

    The heart is located just slightly forward of the girth strap (ie used to hold a saddle in place) on the lower left side. The girth strap can be used to hold a sensor in this area.

    I built the above circuit to learn how this stuff works. I then played with it and tried the speaker to see what affect this would have on the output. You may have read in my other threads about my attempts to build and ECG machine but I was warned off this for fear of causing a heart attack!!!:confused:

    Anyway,,,I removed the speaker last night and after fiddling with different positions I managed to actually get a very very feint pulse in the LED which represented my heart beat!!!. I did this by holding one wire from ground in one hand and the other wire going to the first cap 1uf on the left of the schematic in my right hand. There was a pulse,,very dim but is pulsed 8-10 times. I moved and that was it!!! I couldn't get it again. However, once again I have learned that it can be done, I am still alive and I feel at least I am trying!

    However, I do need help, maybe direction and maybe some ideas.. :p

    I have also seen a scope

    http://www.ebay.co.uk/itm/150620675...X:IT&_trksid=p3984.m1438.l2649#ht_2672wt_1151

    What do you think?

    Thanks

    Justin
     
  17. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    648
    May 8, 2012
    Justin, an EKG is a receiver. It can't induce a heart attack. It measures small electric signals generated by the body. It doesn't pass its own current source through the body.

    The scope looks nice but we need input from other members. I told you that I'm still stuck in the world of analog scopes. You need input from someone familiar with the digital models.

    RE your audio amp. I don't think that's a Piezo element. I don't know Where you got that schematic but I think it's an Electret (Condenser) Mic.

    Chris
     
  18. JPU

    JPU

    281
    1
    May 19, 2012
    Hi Chris

    I ordered the scope regardless. It had some good reviews..Got to wait 10 days though for my new toy.:(

    "Justin, an EKG is a receiver"

    I realise that is the case with the EKG machine. I posted a request for information/help on the Picaxe forum but was told it was not advisable to build my own due to the risk of invoking a heart attack!!! More than one person said that....I gave up asking!:rolleyes:


    The schematic I have included was my doing. I added the small Miniature Piezo Transducer which I purchased from Picaxe as I said I was just playing around..:p The schematic I posted is wrong. I made a mistake in the drawing.

    So,,,do you think I should be trying to achieve my goal by using an EKG machine?

    Justin
     
    Last edited: Sep 15, 2012
  19. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    648
    May 8, 2012
    Justin, I don't know whether to call you a radical impulsive or just plain nuts! How can you determine what a good scope is from reviews? In order for reviews to be meaningful you have to understand the information you're reading. It was only two days ago when you didn't know what an Oscilloscope did. You may well have made a good purchase but you should have waited for input from the group.

    Chris
     
  20. JPU

    JPU

    281
    1
    May 19, 2012
    Chris

    You should know me a little by now!

    I don't mess about...

    I have a goal, and that is to create a heart sensor for a horse!

    If you say scope, I say which one. If you say jump, I say "how high"?

    But no matter what or how much money,,,I will make a horse heart rate monitor for the lay person...

    Call me crazy,,,,frankly "you won't be the first"!!!,,,My mum said that years ago!

    LOL

    Justin

    PS I have just got in from the well!!;) catch up tomorrow!:D
     
    Last edited: Sep 15, 2012
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