GEORGIA INSTITUTE OF TECHNOLOGY
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.
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.
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: / differentialInputs: / (+), (-), and "ground" return
Gain: / 20,000
Bandwidth / 1.7 - 34 Hz
Input Impedance: / 10 Mohms
Input Range: / 200 uV full-scale
Output Range: / 4 volts: from 0.0 to 4.0 volts
Resolution / 0.80 uV/quantum
Input Noise: / < 1.0 uV p-p
CMRR: / > 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.
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.
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 micro-controller 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.
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: ) 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 / 4Number 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