Multichannel Waveform Generator

Multichannel Waveform
Generator
Group 25
Sam Goldfinger, Heng Wei Hsu, and
Chien Tung Shih
Motivation
• To provide electrotactile stimulation as
feedback for myoelectric prosthetic arms
• To simulate skin sensations through outputted
waveforms
Introduction
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9-channel waveform generator
Square, triangle and sine waves available
Variably controlled magnitude of output
Waveforms up to 100 Hz
Outputs limited to 70 volts biphasic
Fits inside of a prosthetic arm's socket
Picture of total circuit
Block Diagram
User Interface / System Control
Waveform Generation
Variable Amplification
Howland Amplifier
High Side Switch
User Interfacing and ControlMSP430
•SPI interface
•AD9833 control
•MCP41010 control
•High side switch
control
•0 or 5 volts
MSP430 output for SDATA,
SCLK and FSYNC
Waveform Generator
Waveform Generation-AD9833
Waveform generation:
Input Signal to AD9833 and
Outputted Square Wave
Waveform generation:
Outputted Triangle and Sine
Wave
Variable Amplifier
Digital PotentiometerMCP41010
• Used a non-inverting
amplifier with a digital
potentiometer
• Controlled the
magnitude of the final
waveform
Variable Non-inverting
Amplification
LM353
F
MCP41010
1k
Howland Amplifier
• Output a voltage based
off the load
• Be voltage limited to a
magnitude of 70 volts
based off amplifier
constraints
Howland Amplifier
Waveform
Howland Amplifier
Schematic and Calculations
High Side Switch Schematic
IN
OUT
GND
Interface to skin
High Side Switch
• Used a zener diode
across Vsg to limit
that voltage drop to
15 volts
• Approximately .5 mA
current into pFET
gate when on
• IN is either high or
low voltage resulting
in passing current or
open
Testing
• Stepped through at each block to verify
waveforms
• With problems interfacing Launchpad with
PCB, we directly inputted signals to variable
amplifier
• Started low voltage until we were confident in
our circuit’s ability
Failed Requirements
• Have the entire circuit on a single PCB
– While we designed the PCB, the aforementioned
interfacing resulted in the use of a breadboard for
functionality
• On a breakout board we were able to control
the digital potentiometer, but we were only
able to have it output a constant 5 kOhm
resistance after the interfacing issue
• Never did human testing because there was
no current-limiting safety feature
Future Work
• Converting the Howland Amplifier to output
constant current instead of voltage
• Connect the MSP430 chip directly to the PCB
to eliminate the interfacing errors as well as
reduce surface area of the PCB
• Test across human skin to verify usage in
prostheses
Cost of Project
Part Number
Component
Number of parts Unit Price
AD9833
Waveform generator
3
5.44
MSP430
Microcontroller
1
10.19
MCP41010
Digital potentiometer
3
1.34
ERJ-2GEJ102X
1k
9
0.1
ERJ-2GEJ104X
100k
21
0.1
PNM0805E5002BST5
50k
9
1.155
LTC6090
Op Amp
3
3.99
LF353
Dual Op Amp
2
0.59
SI3437DV
pFET
9
0.97
SI3460DV
nFET
9
1.7
MMSZ5245B-TP
15v zener diode
3
0.21
JMK107ABJ106MAHT
10uF cap
6
0.32
LMK105BJ104KV-F
100nF cap
3
0.1
GRM155R71E103KA01D
10nF cap
6
0.1
GRM155R71H102KA01D
1nF cap
3
0.1
26.405
Order
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Motivation-sam
Intro-Ct
Block Diagram-ct
Msp430-hw
Ad9833-hw
Lm353-s
Howland-ct
Switch and conclusion-s