Do be patient, I have several other functions to cover here and at home/work.

1. The amp illustrated might be superior to the first one you turned up. I have no EMG experience, so no expertise. I work with insects, but not quite at the level of straight electrophysiology. I suspect that vertabrate nerveous systems are somewhat differently organized - I know they are easier to get at without fatal harm to the organism.

2. The 10 pF is a short circuit to extremely high frequency noise that might be on one electrode lead and not the other. The only effect is to share it with both leads so it becomes common-mode (present on both), and therefore the instrumentation amp will ignore it.

3. If nerve signals to muscles are pulses, then eliminating DC and lower frequencies makes sense. I would want to find out more about any muscle group I was going to instrument to see if there was some superior way to read activity and correctly interpret it.

4. You may have a hard time assembling this project a piece at a time. Perhaps arriving at some working model with all inputs and outputs designated is better. Then you can shop for a processor that can handle the load. Otherwise, you may end up with several not well related mocroprocessors trying to share information.

 

the ultimate goal with this setup(electrode/high pass filter/amp/variable gain amp) is to create a smooth dc signal whose amplitude is proportional to the muscle force so the microcontroller can read it and i can program the proportional output for the air valve. Are you saying i should put everything i can on one board to maximized simplicity and efficiency instead of having multiple connecting wires?maybe both sides of a pcb?

also, if i wanted to measure the signal spikes that are coming from the electrode/amp when i contract a muscle what would i use. is there a special meter to detect something like that? i just want to make sure each section is functioning properly before i move on.

 

I am suggesting that you need to learn everything you can about the total system. The sum of all the inputs and outputs it will take to control your exoskeleton.

When this started, you stated that you wished to use

a variety of sensors (accelerometers, potentiometers, pressure) to control and predict muscle movement

All these sensors are quite different from and not related to the EMG electrodes. It might seem as if some experimenting would be in order to find which sensor/s are most appropriate for the control inputs.

It occurs, for instance, that the selection of just which muscle to monitor may be challenging. In turn, that would make electrode placement difficult, meaning that a slight misplacement could mess up the input by inadvertently including signals from some other muscle group.

There may be a body of knowledge in existence that comes from experiments in making exoskeletons. One example - http://www.reuters.com/article/healthNews/idUSLP27939120080825

Learning how successful and unsuccessful attempts have worked may suggest avenues to explore other than electromyography. Here is a link with handy references - http://en.wikipedia.org/wiki/Electromyography

 

i have spent hours and hours of research online and off, and the design i have mentioned is the one i believe to be the most efficient, cost effective, lightweight, and simplistic. i plan to use the emg sensors that that ive been asking help with for the big muscle groups so that there wont be much confusion for the sensors. muscles such as the biceps,triceps,pecs,abs, shoulders etc. basically sensors will cover all of these locations; http://www.gotmyhealth.com/images/muscle-groups.jpg. and for the forearms i wont use the electrodes because of the close proximity of the muscles, instead ill be using stretch sensors which changes resistance when stretched independently for each finger.

Im just trying to educate myself on circuitry tools and design on this forum. which brings me back to my original question, is there anything i can use to test/see the signal spike output which occurs upon muscle contraction from my electrode/preamp design? would a multimeter work?

 

No, not very well. Something like an oscilloscope is the tool for visualizing voltage signals. An analog type is best for that application, but you may also find it a handy tool to see what your logic is doing.

I have a Tektronix 2221A dual channel 100 MHz storage o'scope. Very good for analog, marginal for logic due to limited bandwith. The storage function is handy for infrequent waveform capture. If you go for an oscilloscope, get the most expensive critter you can afford. Meters are great, but do not approach an o'scope for sheer utility.

I believe we have had some threads in the General section about oscilloscopes.

 

what about one that uses my laptop as a medium like this: http://www.hobbyengineering.com/H1976.html . or will i be able to see these signal spikes anyway when its all connected and i program the microcontroller?

 

Maybe. I can't get excited with 8 bit reso (that is one part in 512. 10 bits is one part in 2048, for lots more detail.), or a 200 KHz bandwidth, although that may let you see most of the activity. I don't know you circumstances, but see if you can get a demo of a digital vs. an analog oscilloscope. It is so easy to alias and miss analog waveforms on low-res digital equipment.

Myself, I would drool over a rebuilt Tektronix 545, although tube o'scopes are not smart these days. I have no idea of your budget, but spending money on an o'scope is a great investment in test equipment.

As far as seeing the activity, you might want to look into typical pulse frequencies and durations to see what the equipment needs to be able to display.

 

hey im trying to buy the components for assembly to the schematic i posted but im not exactly sure the material of the capacitors in this pic: http://mxp.physics.umn.edu/s02/Projects/Muscle/EMG-Filters.JPG . i could use some help, thanks.

 

The leftmost small yellow cap is a ceramic - probably small value. The rear roundish yellow caps ar tantalum. The reddish ones in the near part of the photo could be almost anything. They may be some sort of film caps.

Can't make out markings - no idea of voltage or capacity.

 

the apparatus is run on a 9v, would it be fine if i used POLYPROPYLENE as the material?

http://media.digikey.com/photos/Panasonic Photos/ECQ-P6562JU.JPG

 

Sure. Better accuracy for timing.

 

im having trouble finding a couple parts. r1-80.6ohm,r2-50kohm,r-3174kohm,r4-324kohm,r5-49.9kohm, all metal film. is there a website i can find these parts with the resistance mentioned. digikey sells them but in bulk(5,000), and futurlec doesnt have them either. are those resistances flexible or do they have to be exact?

 

Look in Digi for Yaego 1% film resistors. They are available in quantities of 5. R2 is going to have to be 49.9K - you only get 50K in potentiometers.

 

can you take a look at R5 on the right hand corner of this schematic. http://images.google.com/imgres?img...mages?q=emg+circuit+schematic&hl=en&sa=N&um=1 . so is it a miss marked potentiometer, or did the designer just mess up the resistance?

 

also, what is the blue box on the left bottom portion? http://images.google.com/imgres?imgurl=http://mxp.physics.umn.edu/s02/Projects/Muscle/EMG-Electrode.JPG&imgrefurl=http://mxp.physics.umn.edu/s02/Projects/Muscle/Project_Report.htm&usg=__PASjfhZDFJCaAomCvCiFk9nYrVc=&h=470&w=640&sz=44&hl=en&start=15&um=1&tbnid=vlb5UoRQxQQHUM:&tbnh=101&tbnw=137&prev=/images%3Fq%3Demg%2Bcircuit%2Bschematic%26hl%3Den%26sa%3DN%26um%3D1

 

Sorry, I am confused. The schematic is the map of the circuit, and comes up when you click the "schematic" tab at the left of the page that loads following your link. R5 is a 50K potentiometer.

The pictures in Figures 1, 2, & 3 are of the built circuits. They are not schematics. I am not clear about which figure you refer to, nor does one appear to have a blue box in the bottom left.

The power conditioning portion has a type 64W trim pot in the foreground. The body of the pot is blue (3/8" square) with an adjustment screw visible on the top left of the trimmer.

In the figure of the electrode amp, there is a resistor visible at the right. I can see that the third band is blue, so it has to be the 80.6 ohm (blue is the color code for 6) gain setting resistor.

 

sorry, my links didnt exactly direct you where i had wished, hence the confusion. so the blue pot that you mentioned was the "blue box" i was talking about, but i didnt see it on the schematic for the power conditioning portion, although i did see it on the apparatus. there are only 49.9ohm resistors refered to on the power conditioning portion of the schematic. am i missing somthing? where is it labeled on the schematic?

 

There is no relationship between parts location in a circuit and their location in a schematic. Finding R5 with power conditioning components is no problem. It is R5, and sets the output level of U2B.

Those resistors, R8 & 9 are 49.9K, by the way. They make a voltage divider so the output of U2D will be halfway between Vcc and ground - the pseudo ground.

You might find our Ebook chapter on schematic symbols of interest - http://www.allaboutcircuits.com/vol_5/chpt_9/index.html