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ECE 345

ECE 345. SENIOR DESIGN. ELECTRONIC ASSIST FOR PARAPLEGIC BIKING. TEAM 33. Jiten Patel. Nirav Thakkar. Paraplegic. Paraplegic: Inability to use the lower part of the body Physiological Effects: Muscle atrophy Release of harmful chemicals/bacteria into blood

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ECE 345

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  1. ECE 345 SENIOR DESIGN ELECTRONIC ASSIST FOR PARAPLEGIC BIKING TEAM33 Jiten Patel Nirav Thakkar

  2. Paraplegic • Paraplegic: Inability to use the lower part of the body • Physiological Effects: • Muscle atrophy • Release of harmful chemicals/bacteria into blood • Deterioration of cardiovascular health

  3. Solutions • Design a system that stimulates leg muscles to combat physiological effects • Model system to a recreational activity • Aim for increased mobility… • BICYCLE!

  4. Major Components • Pedal Unit: Determine pedal location • Microcontroller • Interpret signals from Pedal Unit • Drive Shock Box transformer • Switch output between muscle pairs • Shock Box: Produce muscle stimulus

  5. Block Diagram Pedal Unit Microcontroller Shock Box Waveform Leg Muscles

  6. Pedal Unit – Options • Sensor selection • Reflective object sensors • Light sensors • Sensor placement • Rotating (on pedal shaft) • Stationary (on side of bicycle) • Signal reliability • Wireless • Wiring

  7. The Winners • Reflective object sensors • Less space • Less hardware • Rotating sensors • Avoid ambient light • Less hardware • Easier coding • Hard wiring • Less space • Avoid serial data transmission

  8. PU Circuit Design

  9. Mechanical Design - Cu Rings

  10. Mechanical Design - Sensor Bar

  11. Mechanical Design - Contacts

  12. C Functionality • Take signals from PU and determine if muscles need to be shocked • Control BJT to drive transformer • Switch signals between the two muscles pairs

  13. Software Flowchart Check Sensors 01 or 10? Output 10 pulses (360 s) Start 33.33 ms Delay Set Switches LQ/RH or RQ/LH?

  14. Output Waveform 1 2 3 4 5 6 7 8 9 10 5 V 360us

  15. Shock Box Specs • Output 150 V DC pulse • Pulse width of 350 µs ± 50 µs • Pulse frequency of 30 Hz (every 33 ms) • Rectangular pulse • Maximum current of 10 mA • Switch 150 V between two electrodes

  16. Powering the Shock Box • A large battery bank • Too bulky • Uncommon power source • Charge capacitor using Microcontroller • Would not consistently be 150 V • Would damage the Microcontoller

  17. Best Option • Transform a 12 V source to 150 V • Allows Microcontroller to control output • Isolates the 5 V Microcontroller output from the 150 V output pulse • Uses a small/common power source • Possible to create a continuous 150V pulse

  18. Building a Transformer • Basic Idea • Coils ratio of 1:15 • Blue Core • Requires a current amplifier • Built the core and experimentally found results • Inductances on primary and secondary • Step-Up Voltage • Requires high frequency pulsing • Allows for smaller transformer • Maintains a more rectangular output

  19. Transformer Design

  20. AC to DC • Rectify Output • Use RC circuit to stabilize output at 150 V • Control time constant • Small enough? • Big enough?

  21. AC to DC Design

  22. Final Shock Box Circuit

  23. Shock Box

  24. Switching 150 V • High Voltage MOSFET’s • Excessive Complexity • Silicon Controlled Rectifier (SCR) • Trouble with high voltage • More Hardware • Optoisolator • Simple Design • Works for high voltage

  25. Shock Pulses 150 V max 33 ms

  26. Shock Pulse (expanded)

  27. Mechanical Challenges/Successes • Mechanics • Determined pedal position while cycling • Reliable contacts despite rotation • Unhindered pedaling • BICYCLE FULLY OPERATIONAL

  28. Electrical Challenges/Successes • C • 10 pulses • Frequency of 30 Hz (33ms period) • C FUNCTIONAL • SB • Created 150 V pulse • Difficult to obtain  5 mV • Obtained 145 V  5 V • Rise and Fall times vs. Ripple • Power considerations • Current into body • Time constant issues

  29. Riding into the Sunset • Varying stimuli • Safety (redundancy) • Build bike from scratch • Bicycle for outdoor use

  30. Thank You • Professor Philip Krein • Professor Steve Franke • Professor Jennifer Bernhard • Professor Gary Iwamoto • Chuck Henderson • Greg Cler • Wojciech Magda

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