Appliance Operation for the Severely Disabled

Appliance Operation for the Severely Disabled James Miller Tameem Mohsin ECE 345, Spring 2003

Overview of Presentation • Abstract • Introduction • Design procedure • Design details • Design verification • Cost • Conclusions

Abstract • Goal: create an instrument that will allow severely disabled people to operate household appliances. • Instrument must be able to operate wirelessly. • Instrument must be “stand alone.” • Instrument must use biopotentials as source of electrical signal.

Our Vision

Introduction • A single motor unit has an amplitude of 100 micro-volts. The biopotential signal must be amplified. • A transmitter circuit must analyze the source of the amplified biopotential signal. • The biopotential signal must be wirelessly sent to the receiving circuit. • The receiving instrument must determine the source of the signal and determine whether to turn on or turn off the respective instrument.

Design Procedure • Acquire biopotentials. • EMG amplifier circuit. • Transmittal board. • RF. • Reception board. • LEDs representing appliances.

Design Procedure 1: Acquiring Biopotentials • Biology of an EMG signal. • Positioning the electrodes. • V+, V-, GND. • Small versus large displacement. • Size of the electrodes. • Alligator clips. • BNC connectors. • Reducing noise.

Design Procedure 2: EMG Amplifier Circuit • Differential Amplifier. • Bandpass Filter. • Inverting Amplifier. • Rectifier.

Stage A: 10 M-ohm and 2.2 M-ohm. Stage B: 100 k-ohm, 1 k-ohm. Stage A gain: 10.0. Stage B gain: 100. Theoretical Gain: 1,000. Actual Gain: About 800. Design Procedure 2a: Differential Amplifier

Design Procedure 2b: Bandpass Filter • Desired frequency cutoffs: under 60 Hz and over 300 Hz. • Achieved 78 Hz and 256 Hz. • Reasons for cuttoffs. • 60 Hz noise. • Artifact motion noise. • EMG frequency response is between 5-300 Hz.

Differential Amplifier 2c: Inverting Amplifier • 2 k-ohm and 1k-ohm resistors used. • Vo/Vi=(-Rf)/(Ri) • Kept the gain small to avoid “clipping.” • Inverting amplifier used to for increased bandwidth and lower output impedence.

Differential Amplifier 2d: Rectifier Used the same resistor values as inverting amplifier. Positively corrects all voltage values.

Design Procedure 3: Transmittal Board • 555 Timer #1 • Counter #1 • MUX • RF Transmitter

Design Procedure 3a: 555 Timer #1 • C = 0.1 mF Ra = 5 MW Rb = 5 MW • Theoretical Values: T = 1 sec f = 1 Hz duty cycle = 66.7% • Calculated Values: T = 1.17 sec f = 854.7mHz duty cycle = 66.7% • % error = 14.5%

Design Procedure 3b: Counter #1 • Counts from 0 to 3 and then resets • Output used to select biopotential and frequency • Measured Values: Qa: T = 2.32 sec f = 431.13 mHz duty cycle = 50% Vp = 4.187 V Qb: T = 4.65 sec f = 215.05 mHz duty cycle = 50% Vp = 4.125 V

Design Procedure 3c: MUX • Inputs - 4 EMG circuits • Counter cycles through the 4 signals • Output goes to RF Transmitter

Design Procedure 3d: RF Transmitter • HP Series-II RF Transmitter • Counter selects operating frequency • Each signal has a different frequency • Frequencies corresponding to signals: EMG CKT #1 903.37 MHz EMG CKT #2 907.87 MHz EMG CKT #3 912.37 MHz EMG CKT #4 919.87 MHz

Design Procedure 4:Receiver Board • 555 Timer #2 • Counter #2 • RF Receiver • DMUX • D Flip-Flops • LEDs

Design Procedure 4a: 555 Timer #2 • C = 0.1 mF Ra = 820 kW Rb = 820 kW • Theoretical Values: T = 164 ms f = 6.09 Hz duty cycle = 66.67% • Calculated Values: T = 197 ms f = 5.07 Hz duty cycle = 66.5% • % error = 16.75%

Design Procedure 4b: Counter #2 • Counts from 0 to 3 and resets (same as counter #1) • Used to select frequency of receiver • Used as select bits of DMUX • Calculated Values: Qa: T = 391 ms f = 2.558 Hz duty cycle = 50% Qb: T = 784 ms f = 1.275 Hz duty cycle = 50%

Design Procedure 4c: RF Receiver • Operates at same frequencies as transmitter • Needed way to determine origin of signal • All 4 frequencies scanned before frequency of transmitter is changed • If signal, then right frequency and know origin of signal • Output then goes into DMUX

Design Procedure 4d: DMUX • Line is selected by Counter #2 • Same select bits as receiver • Output will go to device specified by the frequency

Design Procedure 4e: D Flip-Flops • If value incoming signal is logic 1, then toggle output • Use XOR gates • Counter used to clock flip-flops • Output goes to LEDs representing devices

Design Details:Components • Components • LM741 Op-Amps. • Electrodes and Electrolyte Gel. • Chips used. • RF information. • Diodes.

Design Details:Diagrams • Layout of the LM741. • Printed Circuit Board. • Overall EMG Circuit. • Overall RF Circuit. • Transmitter Circuit. • Receiver Circuit.

Design Verification: Testing • Differential op-amp inputs and outputs. • Rectified signal. • Ability to see EMG waveform as a function of muscle contraction. • LEDs responded to specific EMG outputs.

Output of Differential Amplifier vs. Input

Design Verification: Conclusions • Noise is a major problem in all aspects. • Timing issues are a problem. • The ability for the RF to function. • False positives and negatives.

Cost • Parts: electrodes, PCB, RF. • Labor intensive. • Burning breadboards. • Physical setup. • Cost of repair and replacement.

Conclusions • Project is a realistic idea. • Future enhancements: boot strap power, noise reduction on electrodes, RF, Holtek encoders and decoders. • The main problems: • Electrode noise and attachment. • RF. • Timing issues resulting in false positives and negatives.

Appliance Operation for the Severely Disabled