In the cases of both EOG and EMG signals, the electrical conduction comes from the excitation of a motor unit, which consists of several muscle fibers and motoneurons. These motoneurons stem from the Central Nervous System and are used to control muscles. When this unit is in an excited state, there is a transfer of ions across a cell’s membrane. This transfer of ions changes the electric potential, essentially changing the polarity of the membrane [1].
In the case of EOG signal capturing, the measurement of electrical conduction occurs on the contours of the eyes muscles (i.e. superior/inferior oblique and rectus, and medial/lateral rectus). When the eyes are rotated in a particular direction, the light passing through the cornea is altered where it is later captured by the retina. The retina is composed of seven layers of cells that act as a neural receiver from the network of muscles that act on it [1]. As previously mentioned, the neurons are transmitted through motor units that trigger the muscles behind the eye. Placing electrodes on the sides of the eyes can show which muscles have formed dipoles, indicating the direction in which the eye is turned.
EMG signal captures the muscular activity of skeletal muscles. For the clicking controls of the mouse, the masseter (jaw muscles) will be used.
What does the
electrical signal taken from their muscle of interest look like and why (i.e.
shape when activated/deactivated, signal amplitude, etc)
The electrical signal taken from the EOG-measured muscles shows pulses in either the positive or negative direction depending on the polarity of the particular dipole. The signal shows a DC signal because it behaves like a single dipole and stabilizes once the eye muscles show no more change in retina rotation. Since the EOG signals shows a stabilization in electrical potential when no additional rotation of the eye occurs, the voltage output can determine the degree at which the eye is turned. The magnitude of the EOG plot indicates how much the eye is turned and the orientation with respect to the DC offset indicates the direction at which the eye is turned.
The electrical signal taken from the EOG-measured muscles shows pulses in either the positive or negative direction depending on the polarity of the particular dipole. The signal shows a DC signal because it behaves like a single dipole and stabilizes once the eye muscles show no more change in retina rotation. Since the EOG signals shows a stabilization in electrical potential when no additional rotation of the eye occurs, the voltage output can determine the degree at which the eye is turned. The magnitude of the EOG plot indicates how much the eye is turned and the orientation with respect to the DC offset indicates the direction at which the eye is turned.
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| Figure 1 shows an example of the raw signal from an EOG reading.
The electrical signal taken from the EMG- measured jaw muscles show more spikes, partially due to the several dipoles that are captured by the electrode. The "disorderly" group of action potentials caused by the numerous muscle fibers activated can be seen in Figure 2.
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| Figure 2 shows an example of the raw signal from an EMG reading. |
Using 9V batteries,
the two amplifiers in the INA2126 can produce signals in the range of -9V to
+9V each. What should the gain used for the amplifiers be and why?
The raw signal of an EOG signal ranges from 15 to 200 microvolts [2]. In order for the signal to be in the desired threshold, a gain of 10,000 will be used in order to bring the signal from microvolts to volts. This would lead to an amplitude of roughly 0.15 to 2 volts, which comfortably satisfies the given range of voltage.
The raw signal for an EMG signal tends to be roughly around 260 microvolts. In order for this signal to reach a desirable threshold, a gain of 5,000 would be used. Then, the total amplitude of the voltage would be approximately 1.3 V.
The raw signal of an EOG signal ranges from 15 to 200 microvolts [2]. In order for the signal to be in the desired threshold, a gain of 10,000 will be used in order to bring the signal from microvolts to volts. This would lead to an amplitude of roughly 0.15 to 2 volts, which comfortably satisfies the given range of voltage.
The raw signal for an EMG signal tends to be roughly around 260 microvolts. In order for this signal to reach a desirable threshold, a gain of 5,000 would be used. Then, the total amplitude of the voltage would be approximately 1.3 V.
Using the INA2126
datasheet, what should the value of the gain resistor R_G be, given the above
information?
The value of the gain resistor should be 8.0 ohms according to the designated gain for the EOG signal.
The value of the gain resistor should be 16.0 ohms according to the designated gain for the EMG signal.
The value of the gain resistor should be 8.0 ohms according to the designated gain for the EOG signal.
The value of the gain resistor should be 16.0 ohms according to the designated gain for the EMG signal.
References
[1] (2001). Fundamental Concepts in EMG Signal Acquisition. [Online] Available:http://www.delsys.com/Attachments_pdf/WP_Sampling1-4.pdf
[2] (2006). QUADRIPLEGIA (In Encyclopedia of Special Education: A Reference for the Education of the Handicapped and Other Exceptional Children and Adults.) [Online] Available: http://www.credoreference.com/entry/wileyse/quadriplegia
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