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- Posted on
February 17, 2007, 8:42 am
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3 out of 5
(Second request - edited)
Seems that a VERY basic EMG device could be constructed with a handful
of off-the-shelf parts. From browsing the group, I've seen where
these are often class projects.
Thanks to the group, I've been given some links to block diagrams, but
I need more detail - parts values and a wiring diagram.
Purpose - Determine specific muscle maximum output.
Input- Standard skin electrode pair.
Output - LEDs preferred over sound. I visualize a simple string of
Requirement - no programmable chips.
Application - I severed the median and ulnar nerves (and a bunch of
other stuff) just above the elbow. After a couple surgeries, I've
gained some motion in my thumb, and I'm trying to exerecise it to the
max muscle activity level, yet stop before the muscle is
I've used a commercial unit in the Occupational Therapy clinic, but
with many bells and whistles that I don't need - LCD display with mmv
readings, timers, sound options, etc.
The commercial unit displayed readings of 10 to 60 mmv, depending on
pad placement and fatigue level. With luck, this will increase, but I
don't know what normal limits are, and don't expect to get anywhere
near normal levels - 100 mmv max should be adequate. Changing ranges
would be a nifty.
Unit must be cheap - crude, if need be. A simple gazinta / comesouta
is fine. Lights or meter for indication. On the lines of a science
fair project would be adequate.
Seems it could be done with a power supply, amplifier, and LED driver
chip, or maybe easier. I've got a well stocked junk box. Working
definition of 'junk box' - 'Term used by electronics hobbyists
describing that assortment of parts, usually acquired over an extended
amount of time from numerous sources, with condition ranging from new
and still in original packaging to new or used and mounted on boards
or sub-assemblies.' We're not talking about a shoe box here. You
should ask my wife. :)
As far as skills, that's changed a tad, which leads to my request.
I've breadboarded a lot, and made enough basic one-sided circuit
boards to be comfortable with the process. Now, I call whatever I do
'therapy', and often recruit family to hold things for a second. :)
Thanks for the help, and if it can't be done I'll quit bothering the
The input circuitry for EMG is very similar to that used for
EEG and ECG. Basicly a high CMMR, differental amplifier with
a lot of gain. The difference is in the filtering, and what
you do with the output. Though in EEG and ECG they are trying
to filter out the muscle (noise) signal, that you want to
I used to work in Biomedical Engineeing at the U of Minnesota
Hospitals, but would have to dig to come up with a design
from a "handfull of off-the-shelf parts"...for what I assume
you want to do cheaply(?). What are your skills electronics?
Try posting your request over on the newsgroup:
Google: EMG circuit schematic
I got lots of good hits, including:
This should do what you need for the front-end. Instead of
sending the signal to a computer you could try driving an LED
You may need to put some signal conditioning circuitry
between the input and the display, but I'll leave it there
for others to help.
As my flight instructor used to say: "Do good work...and have
I've designed such devices, but I have to say - you want to be very
in hooking yourself (however indirectly) to the power line.
when you talk about getting your parts from a "junk box".
I'd recommend that you keep power demands low enough that you can run
a smallish battery.