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Anti-nap device

Anti-nap device. Group 25 – Danny Chan, Vincent Ho, Kin Lai. University of Illinois - Spring 2008. The anti-nap device. Introduction. People may fall asleep at undesired times The anti-nap device can help the user stay awake Helps improve productivity. Objective.

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Anti-nap device

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  1. Anti-nap device Group 25 – Danny Chan, Vincent Ho, Kin Lai University of Illinois - Spring 2008

  2. The anti-nap device

  3. Introduction • People may fall asleep at undesired times • The anti-nap device can help the user stay awake • Helps improve productivity

  4. Objective • Create a low cost pair of devices, one in hand and one in pocket, that can detect when the user falls asleep through a force sensor and uses a vibrating motor to wake them up

  5. Features • Attaches to any writing implement • Range up to 10 feet • Wakes user without causing a disturbance • Delay before activating motor to accommodate accidental release • Two vibrating modes

  6. Overview

  7. Overview

  8. Overview

  9. Sensor - FlexiForce A201 sensor • Sensor changes resistance as force is applied • Can be applied into circuit using voltage division Image and graphic from Tekscan website

  10. Sensor implementation Force sensor Output

  11. Wireless – Linx HP3 series RF modules • Internal antenna (with range over 50 feet) • Very good noise rejection (built-in 28kHz low pass filter on transmitter) • Multiple selectable channels Image from Linx website

  12. Pen device schematic TXM-HP3-900-PPS Force sensor LED Switch

  13. Pen device

  14. PIC – Microchip technology PIC16F877A • Built-in A to D converter • Easily reprogrammable C language architecture Image from Wikipedia

  15. Programming

  16. Motors – Jameco 256365 vibrating motor • 6500RPM vibrator motor, 0.13 oz, 0.28” dia. • Controlled by PIC via a MUX Image from Jameco website

  17. Pocket device schematic PIC RXM-HP3-900-PPS Motors MUX Oscillator

  18. Pocket device

  19. Design changes - Wireless device - Batteries

  20. Wireless device selection • We originally used ES series in the design • HP3 series units have built-in antenna • The HP3 series eliminates the need for an analog to digital converter

  21. Batteries • The ES series has a maximum voltage of 4V, but the HP3 can accommodate up to 13V • Adding batteries to the pen device allows a wider range of voltage from the sensor • The motors were expected to run at 3V, but upon testing, we found they could work at 4.5V

  22. Testing - Power - Wireless range and noise - Force sensor

  23. Power considerations Pen device Limitations • Draws 19mA constant • Powered by 3 button cell batteries (85mAH life) • Estimated 4.5 hours usage • Most current drawn by transmitter • Battery limited by space considerations • Size vs. lifetime

  24. Power considerations Pocket device Limitations • Draws 38mA – 150mA • Powered by 3 AA batteries (2850mAH life) • Estimated 19 - 75 hours usage • Most current drawn by motors

  25. Force sensor tests • Force vs. resistance • Force vs. output voltage (with 4.5V input)

  26. Device operational range • About 10 feet before noise dominates signal • A tradeoff between sensitivity and range of operation • Encasing the receiver further weakens signal • Abrupt motion will also cause noise

  27. Signal noise issues Receiveroutput without low pass filter Receiveroutput with low pass filter A 10Ω, 100uF low pass filter was built at output of receiver

  28. SNR Input to transmitter Comparison of receiver outputs with and without low pass filter SNR without low pass filter is -10.22dB SNR with low pass filter is 4.62dB

  29. Implementation • Casing of the pocket device was chosen be as small as possible • Pen device was attached onto the clip of a pen • PCBs was designed to be small enough to fit onto the pen and into the casing

  30. Possible improvements • Design should include a signal filter • The threshold voltage should be user adjustable • Better battery lifetime on the pen device • For marketability, the size should be smaller

  31. Thanks to • Our TA Tomasz Wojtaszek • ECE Parts shop’s staff • ECE Machine shop’s staff • ECE Store’s staff

  32. End Questions?

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