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Brain Tissue Stimulator N. Lewis, S. Noel, A. Phillips, S. Skroch University of Wisconsin – Madison, Department of Biomedical Engineering Prof. Willis Tompkins – Advisor Dr. Mathew Jones – Client Problem Statement Circuit Schematic Testing Tested circuit with a 20 V supply & 5 V pulse To develop a multi-channel brain tissue stimulator. This device must generate stimulation current of 1 mA on 16 separate channels. Filter out external electrical noise. Allow each channel to be independently gated on/off. Motivation To learn the circuitry of the hippocampus to better understand learning and memory. Tested circuit with 120 V supply & 5 V pulse. Failure most likely due to grounding fault. To improve upon the current tissue stimulation process which is not physiologically accurate. To provide a low-cost multi-channel stimulator. Client Specifications Future Work Trigger each pad independently with a 5V transistor transistor logic (TTL) pulse. Continue testing circuit at higher voltages. Deliver 1 mA of current to each channel. Find method to cut down lag. Deliver the same amount of current to each pad. Active feedback to create constant current source. Deliver the pulse in 100 s with no lag. Rectifier: Takes the AC input signal and transforms it to a positive output. Cost Analysis Potentiometer (5 MΩ) Potentiometers (10 kΩ) Floating voltage source Voltage regulator Optical Isolator Inverter FET Resistors Total (for 16 channels) Circuit Components $8.37 32 @ $0.10 $73.25 $0.99 32 @ $0.44 16 @ $1.32 32 @ $5.25 48 @ $0.06 $363.34 Low-pass filter: Filters out the 60 Hz noise and smoothes the signal from the rectifier into a constant DC signal. Optical isolator: Blocks any backflow of electrons to the computer, which provides the 5V trigger pulse. DC Power supply: Keeps the voltage seen at the gate 12 V above the voltage at the drain in order to keep the FET open. Field Effect Transistor: Acts as a switch. When the gate sees the 5V pulse, it lets the supply voltage (of up to 1000V) through. Capacitive (Cap.) Bypass: Shortens pulse fall time. Add large potentiometers for voltage control. Add more channels. Printed circuit board in finished box. References http://www.superteaching.org/MINDimages/hippocampus.gif Acknowledgements We would like to thank Professors L. Burke O’Neal and Jack Ma for their help this semester.