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G EO RGIA I NS TI TU TE O F TECHN O LOGY
School of Electrical and Computer Engineering
ECE4006 Senior Design
Design Report
February 12, 2002
Digital Impulse Control Group
Wayne Blake
Mary Nsunwara
Reshun Gethers
The purpose of this report is to explain how we plan to carryout the goal of
successfully utilizing muscle potentials to command a remote control car. There are
multiple segments of this project that will have to be addressed. Figure 1 illustrates them
from the front-end to the back-end. On the front-end of this project, the main devices are
the EMG amplifier, the A/D converter, and the computer software. The back-end
consists of the signal to be transmitted and the performance of the remote control car.
Each segment will not have to be implemented entirely from scratch. We have been
given full access to the information of previous design teams. Thus, we are able to utilize
any circuit designs and others resources of information that we feel may assist us in
achieving our goals.
Electrodes
Amp/filters
A/D
Converter
PC
Software
Transmitter
Figure 1. Flowchart of the entire system.
Signal Acquisition
The most important objective at this point in our project to build an effective
EMG circuit. At this point we are not focusing directly on designing an EMG circuit
because we currently have an EMG design in our possession. This design is based on an
older version of the BrainMaster EEG monitor that was given to a previous design group
by the company. A previous design team was able to get this circuit to successfully
measure muscle potentials in the jaw. Thus, we feel that if we duplicate their prototype,
we should have the same success using the circuit as an EMG. The schematic of this
circuit is shown in Figure 2.
Figure 2. EMG circuit schematic.
This circuit consists of two amplification stages. The input amplifier used in the first
stage is the Analog Devices AD620. The circuit is designed such that this amplifier’s
output should have a gain of 50. An integrator circuit is also utilized in this first stage of
amplification. The integrator circuit that is being utilized as a low-pass filter and its
main purpose is to provide good linearity.
The second stage of this amplifier is designed such that it has a gain of 390.
Thus, the total gain of the entire circuit is 19500. The second stage also provides a
frequency response from 1.7 up to 34 Hz. Further efforts may go into redesigning this
circuit because of this current frequency response specification. Since this circuit was
originally designed to detect brainwaves, a frequency response of 1.7 – 34 Hz was ideal.
However, the frequency range of muscle potentials is 30 – 500 Hz. Hence, in the future
we may want to adjust the value of resistor R11 in Figure 2. Making the value of this
resistor smaller should widen the bandwidth of this stage. Once more prototypes have
been built; we will then be able to determine if adjustments of this nature will be
necessary. Table 1 lists some more technical attributes of the current EMG circuit we are
working with.
Type:
Inputs:
Gain:
Bandwidth
Input Impedance:
Input Range:
Output Range:
Resolution
Input Noise:
CMRR:
differential
(+), (-), and "ground" return
20,000
1.7 - 34 Hz
10 Mohms
200 uV full-scale
4 volts: from 0.0 to 4.0 volts
0.80 uV/quantum
< 1.0 uV p-p
> 100dB
Table 1. Other technical specifications of the EMG circuit.
The circuit used as the power supply for our current prototype is shown in Figure 3. The
components included a 7805 regulator, 9V of DC power, and two capacitors. This circuit
was designed to supply a clean and regulated signal.
.
Figure 3. Power supply circuit
Currently, we have an assembled prototype of the entire EEG circuit that was
built by one of previous design teams. Therefore, we have been able to test their model
to try to duplicate their measurements. Unfortunately we have not had any success with
their prototype as of yet. We are hoping this is not a result of the circuit design we are
using. In faith we will rebuild this same model and expect that it will function as it did
previously. We anticipate to have a fair amount of success measuring muscle potentials
utilizing this circuit design. However, we may not be able to achieve the same success
and in turn may have to redesign certain segments of the circuit schematics.
Another option to be taken under considerations is for us to purchase a MindTel
TNG-3B. This device is shown on the next page in Figure 4. It is an interface device
that is specialized for electromyographic use. The TNG-3B has 16 channels in total,
eight analog and eight digital inputs, and also includes a DB9 serial-port connector for
use on a PC.
Figure 4. The TNG-3B Interface device.
Together with appropriate sensors, transducers, and switches, it provides a flexible
system for human-computer interface applications, especially for people with severe
disabilities. The brain of the TNG-3B is its 40-pin microchip PIC16C74A microcontroller integrated circuit. The micro-controller in TNG-3B has been programmed in
Microchip's RISC assembly language. The communication between TNG-3B and the
serial port of a PC occurs at 19.2 kbps. The data stream includes eight bytes for the
analog channels, one additional byte for all eight digital inputs, and either of two
separator (punctuation) bytes of 055h and 0AAh (85 and 170 decimal) that alternate on
successive cycles. Accordingly, the cycle period is approximately 5 ms, and the cycle
rate is approximately 200 Hz. The TNG-3B also has a serial-port test LED. The LED is
driven directly by code in the micro-controller chip. Therefore if the serial port is not
active, then the power from the handshaking lines will absent; thus the micro-controller
will not operate and the LED will not illuminate when the test button is pressed. The
price of TNG-3B is listed as $150 plus $10 for shipping/handling.
The TNG-3B device is managed by software called NeatTools, which can be
downloaded off the web for free. NeatTools is a software application, which allows
users to create data flow networks as shown in Figure 5.
Figure 5. Screen capture of NeatTools software.
Combined with the TNG-3B, NeatTools provides the ability to manipulate any input (a
resistance or a voltage of 0-5 volts) and interpret that input as a command that the
computer understands. It is an object-oriented visual programming environment.
NeatTools works by utilizing tool bars, each with a different set of controllers. The user
creates a NeatTools dataflow network by connecting modules that have been dragged
from toolboxes onto the NeatTools desktop. Also NeatTools programming interface
enables the user to program without typing in the hard code.
Later Revision: We were unsuccessful in acquiring more specifications on the
MindTel TNG-3B. The only contact listed on the website (Edward Lipson:
[email protected]) did not respond to any of our e-mails requesting additional data.
Thus, we suspect that this website is outdated and are no longer considering acquiring or
duplicating this device as an alternative plan.
Signal Measuring Logistics
Once a dependable EMG circuit is obtained, we must then determine the most
optimal techinique in which to acquire distinct signals from various muscles. Muscle
selection will play a significant role in determining the success of the controls aspect of
our project. The issues that arise with muscle selection include contraction speed, size,
and how much of the muscle is covered by fatty tissue. Each of these issues will effect
how we will have to go about designing the end system. For example, the contraction
speed of a muscle group will undoubtedly have an effect on the coding aspect of our
project. There are some segments of our design project that are a bit unaddressable at
this time. Electrode and body movement usage happens to be one of those grey areas.
Until obtain a dependable EMG is constructed, we are somewhat limited to reasonable
speculation.
The monitored activity of muscle potentials can range from less than 0.1uV to as
high as several thousand microvolts. For example, relaxed muscles such as those in the
forehead region generally exhibit voltages in the range of 0.75 to 3 uV. Large muscles
such as the quadriceps can exhibit activity as high as 2000uV. Of course these
measurements are going to vary from person to person. It would not be reasonable for
one to monitor a muscle group as large as the quadriceps for as project of this nature.
Although the strength of the signal of this muscle group is very appealing, one would be
limited by contracting speed and overall usability. Similar projects taken on in the past
have focused mainly on muscles in the head region. The main reason for this is because
the muscle that are located in the head provide the most usability as far as people with
disabilities are concerned. The muscle groups in the head are fairy small compared to the
rest of the body and thus, have faster contraction ability. The previous design group was
able to capture fairly distinct muscle potentials by measuring the muscles of the jaw. So
far using the jaw muscles to control our system seems to make the most sense. We will
need to send at least five basic commands to the remote control car. These basic
commands are forward, reverse, left, right, and stop. Depending on the model of remote
control car we have, we may need the ability to send other commands, i.e. turbo. Besides
the muscles that control the eyelids, the jaw muscles are the simplest muscle to control in
the head region. People have difficulty moving one eyebrow at a time, however it is not
as hard for an individual to bite on one side of their mouth.
Analog to Digital Conversion
Another segment of our project that is under examination is the analog to digital
conversion process. We currrently have a suitable PC card that implements A/D
coversion in our possession. It is the Keithley DAS-1701ST-DA.
Some of its key
specifications are listed below in Table 2.
Number of Inputs
4
Number of Outputs
4
Max Sampling Rate 160 kS/s
Input Ranges
0 - 5V, 0 - 1V, 0 - 100mV, 0 - 20mV
Gains
1, 5, 50, 250
Table 2. Specifications for the current A/D converter.
This particular A/D converter was used by the previous design groups and is the prime
device for us to continue to utilize. However, this component has an ISA bus interface
instead of a PCI connection. Most current computers no longer have ISA interfaces, thus
we would like to have an A/D card that has a PCI connection. We are in the process of
determining whether we will be able to acquire the same A/D converter model with a PCI
connection. We have already obtained the user manual and specification sheet for this
particular model. The Keithley DAS-1701ST-DA A/D converter comes with
DriverLINX package software. This is the software in which the A/D converter is to be
programmed with. In other words, we will be using this software to decode the signals
that are sent to the A/D converter and to determine what signal or command is to be
transmitted to the remote control car. We have not gotten in to deep wth trying to
determine how to go about coding our system as of yet. Ths will not be done until we are
sure about the A/D converter that we will use in our system.
Appendix
I. Amplifier Parts
1. AD620
FEATURES:
-
Gain Range: 1 - 1000
-
Wide Power Supply Range: (+ -) 2.3 V – (+-) 18 V
-
Available in 8-Lead DIP and SOIC Packaging
-
Low Power, 1.3 mA max Supply Current
-
For more information: www.analog.com
2. OP90
FEATURES:
-
Single Supply Operation: +1.6V to +36
-
Dual Supply Operation: (+-) 0.8V to (+-) 18V
-
Low Supply Current: 20u A Max
-
High Output Drive: 5m A Min
-
Low Input Offset Voltage: 150u V Max
-
High Open-Loop Gain: 700V/mV Min
-
Outstanding FSRR: 5.6u V/V Max
-
For more information: www.analog.com