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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 • • • • • • 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 • • • • • • • • Motivation-sam Intro-Ct Block Diagram-ct Msp430-hw Ad9833-hw Lm353-s Howland-ct Switch and conclusion-s