Hands-Free Calculator
ECE 345 Final Project Proposal
Tim Bruns
Caroline Harvey
TA: Ajay Patel
June 23, 1999
Introduction
We plan to design and build a system to perform simple calculator functions without the
use of hands. The calculator will consist of the ten digits, operands, equals sign,
parenthesis, and decimal point. Through the EOG amplifier, the movement of the eyes
will determine the selection of digits or functions. We will use an EMG amplifier
connected to the jaw to select the use of function keys, instead of numbers.
We have selected this project because we are both interested in biomedical engineering
an enjoyed ECE 314/315. This project builds upon some concepts we have learned in
those classes.
Block Diagram
Description of Block Diagram components found in text of Design Considerations.
Design Considerations
Two main types of circuits will be used as the hardware component. The
Electromyogram (EMG) is a biopotential amplifier that magnifies signals due to muscle
activity. When muscles are tensed, there are many extracellular field potentials that can
be recorded by this circuit. These signals are about 0.1 mV – 90 mV in amplitude and 25
Hz – 3 kHz in frequency. Thus our EMG will have a gain of around 1000 and a bandpass
region of 25 Hz - 3 kHz. The Electro-oculogram (EOG) is a biopotential amplifier that
magnifies signals due to eye movement. The eye is essentially a dipole with the cornea
having a higher potential than the retina. Placement of leads to the EOG on opposite
sides of an eye can lead to an observation of a linear relationship about the position of the
eye to 30° off of center. The biopotentials are in the microvolt region and have a low
frequency around 0.1 Hz – 10 Hz. Our completed EOG circuits will have a gain around
10,000 and a bandpass region of 0.1 Hz – 10 Hz.
The EMG amplifier will have a lead placed on the jaw of the subject and a
reference lead placed on an inactive part of the body. Clenching of the jaw will lead to a
signal with much higher amplitude than with no activity. With the use of rectifier and
summer amplifier circuits following the EMG, a flat, almost dc signal will be observed.
Each EOG amplifier will have lead electrodes placed on opposite sides of the eye; one set
on the horizontal and the other on the vertical. Shifting of the eye to different extremes
of vision will lead to pairs of voltages from the two EOG circuits, as in a Cartesian
coordinate system.
LabVIEW will be used as the software component of our project. Output from
the three biopotential circuits will be interfaced to the computer through NI-DAQ and
used to manipulate a simple calculator. The paired outputs from the EOG circuits will
represent one of nine positions on a x-y plane. LabVIEW will be used to determine
which of the positions the paired inputs corresponds to. An internal clock cycle will be
used to determine if the jaw was clenched once or twice in a short time span. If one high
input from the EMG is counted during a cycle then based on the position values from the
EOG inputs, one of the numbers 1-9 will be selected. If two high inputs are detected,
then one of the following will be selected: [0 , . , + , - , * , / , ( , ) , Enter]. Proceeding in
this manner, our project will be able to function as a hands-free calculator.
Specification Tests
A common problem with biopotential amplifiers is that they can have noise due to
amplification of potentials that appear everywhere on the body, or common mode
voltages. To reduce this problem, the amplifier circuits have to be adjusted such that the
common mode gain is minimal and the common mode rejection ratio (CMMR) is
maximal. We will be looking for a CMMR of at least 20,000 that would indicate that
common voltages would be ignored.
In computing the cutoff frequencies and gains of our amplifiers, we are assuming
that the values of the resistors and capacitors are correct. Unfortunately, they are never
100% accurate. For the purposes of our project, we would expect our equipment to be
within 10% of the desired values. We will look at the changes in the output due to
resistors or capacitors that vary from the given value by different amounts. Results from
these experiments will be used for tolerance analysis.
Schedule
6/21-6/27 Proposal Paper,
Order Parts,
Begin Diagramming Circuit
Learn LabVIEW
6/28-7/4 Build Circuitry
7/5-7/11 Test / Debug Circuitry
7/12-7/18 Interface Circuitry with
LabVIEW Software
7/19-7/25 Finish Up Project
7/26-8/1 Demo,
Presentation,
Write Final Paper
Cost
(Labor)
Dream salary: $20 / hour
Hours to complete: 20 hours a week for 6 weeks = 120 hours
Total: $20/hour * 120 hours * 2.5 (overhead) * 2 partners = $12,000
(Parts)
Electrodes: $5
Resistors / Capacitors: $5
Op Amps: 12 chips * $1/chip = $12
Total: $22
Total Costs: $12,022