circuit build for emg exoskeleton, please help

Discussion in 'The Projects Forum' started by whitey111, Jun 21, 2009.

  1. whitey111

    Thread Starter Member

    Jun 21, 2009
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    Hi,

    I'm working on an exoskeleton project that uses a variety of sensors (accelerometers, potentiometers, pressure) to control and predict muscle movement in order to increase strength by means of pneumatic air muscles. I'm currently building trying to build the electrode, but i want my part list to be exact, and i was hoping to find some help here who could help.
    Below is the schematic. can someone give me a parts list for this and help me out with building it?(maybe a program i can test it with)

    electrode schematic: http://robotics.hulcoop.com/electrode.bmp

    any help is appreciated.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    This is interesting. None of the sensors you mention use electrodes to function. Do you know the function of the circuit?

    Electrodes are very different from the printed circuit board layout in your BMP. This is the Wikipedia article on electrodes - http://en.wikipedia.org/wiki/Electrode

    The layout appears to be for an amplifier and the parts are all identified. Which one/s can you not make out? The pin-to-pin spacing on the OPA2134 is .1", the INA2128's pins are spaced .050". The other components should be easy to pick out from the size on the PCB.

    Except for the J1 connector. You may have to cruise for mechanical drawings to find one that fits the dimensions.

    Can you make printed circuit boards? If not, search on the topic and you will find several threads that deal with both programs and the making of them. If you use some software app to make the PCB, then the resistors and capacitors can be in other packages than the ones shown on the BMP.

    The circuit is purely analog - it's much easier to give it a known input and measure the output.
     
  3. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
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    Is that an RJ45, ethernet type, connector for J1? That's the first thing that comes to mind looking at the footprint...
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    Might be, but what function would a specialized connector like that serve in an analog amp circuit? Sure doesn't use all 8 pins.

    On third thought, that must be an RJ-45 connector. Good eye.
     
    Last edited: Jun 21, 2009
  5. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
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    It might be as simple as convenience. It is a nice twisted pair cable and may be common in the system.
     
  6. whitey111

    Thread Starter Member

    Jun 21, 2009
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    First of all thanks for all of the responses.
    Maybe this might shed some light on the situation. my design involves the following stages. please correct me if one is out of order. muscle movement->electrode->amplifier-> variable amplifier(to distinguish torque control)->arduino microcontroller->driver-> proportional control valve-> pneumatic air muscle actuator. the other sensors will give the microcontroller more intell on the exact movments; stop, start, pressure control, etc.. im now trying to build the amplifier and variable amp and electrode setup as simply as possible. is there an instructable for this? i have no confidence in my ability to read schematics, thats why i asked for the list of components, here is the full page that im using; http://robotics.hulcoop.com/4.html , just scratch the main control board, i wont be using that. Heck, if there is a website where i can purchase the amp components fully assembled i would be estatic, because that would cut my production time. any help is appreciated
     
    Last edited by a moderator: Jun 22, 2009
  7. beenthere

    Retired Moderator

    Apr 20, 2004
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    The schematic for that PCB is the one on the linked page just under the muscle illustration. I don't think too much of the designer, as there is a section of the dual instrumentation amp not connected. That is simply wasteful.

    If I might observe here - you are going to have an uphill fight if you are struggling with schematics. Usually, that is a matter of - like all else - practice. The bitmap you posted is the PCB that follows the schematic. You might look at both and see if you can follow the schematic on the PCB layout.

    It would make more sense to substitute a single instrumentation amp for that INA2128. Something a bit older like an INA111 will come in a DIP8 package like the dual op amp, and be easier to handle.

    Back to an earlier question - can you make your own printed circuits?
     
  8. whitey111

    Thread Starter Member

    Jun 21, 2009
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  9. whitey111

    Thread Starter Member

    Jun 21, 2009
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  10. beenthere

    Retired Moderator

    Apr 20, 2004
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    The instrumentation amp is more the thing, but do you need a 20 Hz high pass function? What is the intended function of the electrode input?

    This is not designing on your part - just shopping for parts. What expertise do you bring to this project?
     
  11. whitey111

    Thread Starter Member

    Jun 21, 2009
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    Some of the most advanced equipment is the accumulation of many intricate technologies put together in a different way to form a new invention. this is one of hundreds of devices that i will use in syn with eachother to create something completely new. my unique designs comes further into the project when all the "simple" stages like this are fully complete. this is the lemon next to the pie. my inability to buy this system has forced me to learn circutry design and building techniques so that i can move forward with my designs. i am simply asking for some help along the way in this learning process.

    the application for the electrode is to create a biosignal which in turn controls a pneumatic actuator.

    is there any way you can help me out with the schematic component values?
     
  12. beenthere

    Retired Moderator

    Apr 20, 2004
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    As far as I can see, all component values are indicated on the schematic. Are we talking past each other here? I am specifically referring to the second link which leads to n actual schematic. A schematic is a map that indicates all the connections between components in the circuit.

    The circuit is labeled as an EMG amp, so it could be useful. You have not stated what the circuit is to monitor, so I can't guess what the electrodes attach to, or if the output is suitable for your needs (recall there is a high pass filter that discriminates against signals below 20 Hz). How, for instance, does the pneumatic actuator actually get controlled? Is the control loop purely analog, or does a computer mediate the inputs and outputs?
     
  13. whitey111

    Thread Starter Member

    Jun 21, 2009
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    well any surface emg signal monitors the biosignal given by the muscle(upon contraction) on your body where the electrode is touching, then the amplifier creates a frequency thats detectable. I guess what im having trouble with in detail is what the letters stand for such as c5 10p capacitor, what is the conversion/numeric/equation value so that i can find the actual part number on digikey.
     
  14. beenthere

    Retired Moderator

    Apr 20, 2004
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    C5 is the circuit identifier for reference purposes. 10p means it's a 10 picofarad value. Any 10 pF cap will be non polar, and any voltage rating over 25 will work. The biggest worry in selecting such a component is the lead spacing so it agrees with the layout.
     
  15. whitey111

    Thread Starter Member

    Jun 21, 2009
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    ok, thanks. does the tolerance matter in these circumstances, and what about the material. is there a certain tye of capacitor that is used in the amplifer design such as ceramic, mylar, mica, polystyrene, etc...

    and i would ask the same question for the resistors, materials, tolerance etc...
     
  16. beenthere

    Retired Moderator

    Apr 20, 2004
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    For best results, assume all resistors to be 1% film, and all caps should have the lowest tolerance - 5% - 2% depending on what is available.

    Weenie caps like 10 pF units are always going to be ceramic.

    How's your skill set? It's going to be handy to be able to read schematics and be able to make PCB's from same. If you are really going to get into the design aspect, learning lots of electronics as well as programming will be helpful. Being able to do machining and welding sounds useful, too.
     
  17. whitey111

    Thread Starter Member

    Jun 21, 2009
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    i was thinking in the long run it would be cheaper to go to this site for the printed circuits rather than buying all the materials to make it myself : http://www.expresspcb.com/ . i am very good with machining and welding and mechanical engineering. i have no experience with programming however. is there a book or website on programming that you would recommend?
     
  18. beenthere

    Retired Moderator

    Apr 20, 2004
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    No, but only because I learned long ago. I do assembler, which is probably better for your application, if for no other reason than it gives superior access to hardware and will be less bulky than a high level language like C.

    Someone will probably step in a disagree - it is sort of personal preference as to what form you come to prefer programming to take.

    While there are outfits that will make prototype PCB's, the software they make available is very limited if you decide to do SBC work (single board computer). You will almost certainly need a real CAD program (expensive) to do the work.

    This project promises years of toil and expense. You will learn a lot, though. Think kicking Iron Man's heinie.
     
  19. whitey111

    Thread Starter Member

    Jun 21, 2009
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    ha, iron man is going down.

    i see what you meant about the designer in one of my early posts and how he left part of the dual amp not connected, i was wondering what you thought of replacing it with the ina126 used here:
    http://mxp.physics.umn.edu/s02/Proje..._Schematic.htm .

    also i was thinking about what you said when you asked if i needed the 20 Hz high pass filter. i was thinking that current that flows through the body at all times which the electrodes/amplifer pick up would explain that. maybe anything higher than the 20 hz input would signal a movement in the muscle which is what im trying to detect with this system.

    also i was wondering what the purpose of the 10p capacitor is between the positive and negative lines of the electrodes in this page; http://robotics.hulcoop.com/preamp.bmp .because i havent seen anything like that in other emg amp designs such as the first post.

    To answer your question on how the pneumatic acutator gets controlled; i think the best solution would be a microcontroller(http://www.robotshop.us/arduino-mega-usb-microcontroller-board.html) that has a voltage regulator and maybe a driver depending on what type of valve i use.
     
  20. whitey111

    Thread Starter Member

    Jun 21, 2009
    19
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    ---------Bump^
     
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