Pressure Sensor for Peripheral Neuropathy
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Pressure Sensor for Peripheral Neuropathy Group 19 Pankil Dharia Zachary Hafez Mustafa Manzoor Agenda Introduction Objective Review of Design Functional Tests Successes and Challenges Marketing Factors Recommendations Questions Introduction People who suffer from peripheral neuropathy are left with partial or no feeling in their limbs. They often bump or scrape these limbs unknowingly, which leads to infection and possible amputation. According to the Neurology Channel Online (http://www.cnn.com/2006/HEALTH/conditions/01/27/rar e.conditions/index.html), Peripheral Neuropathy affects at least 20 million people in the United States. Nearly 60% of all people with diabetes suffer from peripheral neuropathy Objective We want to construct a product that senses when trauma to the foot has occurred, alerting the user of potential injury. Pressure sensors will be located on each toe, which are the most vulnerable to trauma in patients with neuropathy of the foot. Temperature sensors will be included to alert the user that their skin is in danger An alarm and corresponding LEDs will activate when a traumatic event is detected by the sensors Design of the Product Objective (cont.) Benefits: – Instant notification of possible traumatic event – Low cost – Comfortable – Adjustable – Light weight and discrete – Portable – Commercially recreational – Reduced probability of dangerous infection – User friendly Objective (cont.) Features: – Various pressures and temperatures sensors – Multiple sensor locations for distributed sensing – Identification of traumatic event to assess possible damage – Visual output for corresponding notifications – Distinct sound output (alarm) for dangerous pressures and temperatures for audible notification – Adjustable strap for variable location – Easy to use reset button – Multi-colored LEDs for differentiating causes of trauma – Battery operated (+9V) Review of Design Review of Design Review of Design Power: 1 8 +9V 0.1u 2 7 MAX1044 Switched-Capacitor 3 6 10u Voltage Converter 10u 4 5 -9V Output 9V Battery powering entire device -9V produced by the above circuit Review of Original Design Review of Design Pressure Sensors: 25lb. Flexi Force Pressure Sensors(A201-25) Sensors placed on each digit The pressure exerted on the force transducer will vary the resistance in the sensor When a certain voltage threshold is reached, an alarm will sound with LED notification ® Tekscan Review of Design Temperature Sensors: Ametherm Thermistor (NT05-5029) Sensors placed on the sides of the foot As temp. increases, resistance decreases When a certain high or low threshold is reached, an alarm will sound with corresponding LED notification ® Ametherm Review of Design Review of Design Operational Amplifier: Sensors output low voltages in millivolt range Operational amplifiers amplify the input voltage of the Flexi-force transducer by 50 times to about 2-5 Volts Output signal sent to the comparator for further analysis Review of Design Review of Design Comparator Circuit (Pressure): Circuit uses a comparator with Vref set to 3V Vref corresponds to the 5lb/(inch^2) threshold pressure for pain If input signal >= Vref – Comparator outputs a logical high to the alarm system If input signal < Vref – Comparator output will remain logically zero Review of Design Comparator Circuit (Temp.): If input temp > 50°C Resistance across Thermistor decreases Increases current and input voltage to comparator Triggers comparator to output logical high signal when input voltage >= Vref (3.12V) If input temp < -5°C Resistance across Thermistor increases Decreases current and input voltage to comparator Input voltage amplified with gain of 10 Triggers comparator to output logical high signal when Vref (4.0V) >= input voltage Review of Design 2K 5.1K 1 8 1 8 Rg Rg Gnd Vcc +9V 2 7 2 7 -In +Vs +9V +In Output 3 AD622AN 6 3 LM311N 6 +In Output -In Bal/Strobe 4 5 +9V 4 5 1.5K Output to System Design Block -Vs REF Vee Bal 20K 750 FlexiForce Sensor -9V Block 560 Pressure Sensor Circuit Review of Design 1 2K 8 Gnd Vcc +9V 2 7 +In Output 3 LM311N 6 +9V 5K Ohm Temp. -In Bal/Strobe 1K Thermistor +9V 4 5 5.2K Vee Bal Sensor 1.1K -9V Block Circuit 1 Rg 2K Rg 8 1 2K 8 Gnd Vcc +9V 2 7 -In +Vs 2 7 AD622AN +9V +In Output 3 6 20K +In Output 3 LM311N 6 -In Bal/Strobe 4 5 -Vs REF 1K 4 5 Vee Bal -9V Block -9V Block Output to L-O-S Block Output to L-O-S Block (Cold) (Hot) Review of Design Review of Design Latch: An S/R latch (CD4043BE) is used to hold the signal once it has been triggered even after the input has been removed. Latch will enable the user to reset the alarm after being notified. The latch will reset the speaker alarm as well as the 3 LEDs. Review of Design Review of Design Speaker: This will output a sound to alert the user of hazardous conditions. The 3 latch outputs are ORed and sent to the speaker The speaker is triggered when either latch (pressure, cold temp., hot temp.) is set to high Review of Design LEDs: Different colored LEDs are used to distinguish between temp. and pressure Red coincides to a temperature >= 50°C Yellow coincides to a temperature <= - 5°C Green coincides with a pressure >= (5lb/inch^2) Review of Design +9V 0 Vcc1 1 16 a1 b1 1 12 Input from Inv. in 2 15 System Design a2 CD4043BE b2 C2 C1 Block (pressure) 3 a3 b3 14 3 10 4 13 a4 b4 5 12 Switch a1 b1 4 9 6 a2 b2 11 C4 C3 Input from 7 10 6 7 Comparator Block a3 b3 (Hot) 8 9 a4 b4 GND 0 Pressure Input from LED Comparator Block (Cold) 10 K Cold Temp. Output LED 10 K Hot Temp. to System 10 K Latch-Switch- LED Design Block (NOR gate) Output Block Output to System Design Block Output to System Design Block (NOR gate) (NOR gate) Review of Design Input from L-S-O Block Input from L-S-O Block Input from L-S-O Block +9V Amp-Comparator Block for Pressure (1) Pressure 1 14 a1 b1 2 13 Amp-Comparator Block for Pressure (2) a2 b2 Overall Sensor Amp-Comparator Block for Pressure (3) 3 4 a3 a4 SN74LS260N SN74LS260N b3 b4 12 11 5 NOR Gate 10 Circuit a1 b1 System 6 a2 b2 9 Foot Amp-Comparator Block for Pressure (4) 7 8 a3 b3 Blocks Design Amp-Comparator Block for Pressure (5) Block Temp. Sensor Circuit Comparator Block for Temperature +9V 1 14 a1 b1 2 13 a2 b2 L-S-O Block L-S-O Block 3 12 a3 b3 Output to Output to (Cold) (Hot) 4 11 SN74ALS04BN a4 b4 5 a1 Inverter b1 10 L-S-O Block (Pressure) Output to 6 9 a2 b2 7 8 a3 b3 Latch-Switch-Output Block Speaker Functional Tests Pressure sensor without amplification Channel 1: Input Channel 2: Output from pressure sensor Functional Tests Pressure sensor with amp. (Gain = 5) Channel 1: Input Channel 2: Output from pressure sensor Functional Tests Comparator Circuit Channel 1: Input to comparator Channel 2: Output showing logical high when Vref (3V) is exceeded by input signal Functional Tests Temp. Input With Corresponding Comparator Output 3 2.5 2 1.5 Volts 1 Comp. Output Input 0.5 0 -0.5 -1 -0.000006 -0.000004 -0.000002 0 0.000002 0.000004 0.000006 Seconds Functional Tests Oscilloscope reading of Thermistor Response Functional Tests Pressure Sensor: – Tested in accordance with known pressures that cause damage to foot – Sensors were first aligned to the tip of each digit of subject. – Tested the sensitivity of the sensors, when mapped to a specific foot. Temperature Sensor: – Exposed to varying degrees of temp. (dry ice -20°C...flame 50°C) Power Supply: – Voltage leaks were tested – Voltages at every component were measured Calibration and Reliability: – The pressure sensors were calibrated to injurious measurements – Damaging forces were tested to ensure reliability of the circuit. Successes and Challenges Successes – Able to run entire device with one 9V battery – After consultation with podiatrist (Dr. Reed), able to achieve specific thresholds – Able to successfully implement a fully-functional model of device Successes and Challenges Successes and Challenges Successes and Challenges Challenges – Calibrating the circuit to work with precision – Amplifying the signals coming from temp. and pressure sensors – Figuring an accurate model for testing the product – Using PTC-thermistors instead of NTC-thermistors – Implementing device on PCB Successes and Challenges PCB Successes and Challenges PCB Successes and Challenges PCB Marketing Factors Part Description Quant. Price Part Description Quantity Price Battery Connection for 9V 2 $1.00 FlexiForce Pressure force 5 $60.00 Connector battery A201-25 transducer (25lb) Speakers Used to notify user of 1 $5.00 Thermistors Temperature 1 $2.00 dangerous-pressure or NT05-5029 sensor with temp. variable resistance LED Light Emitting Diodes 3 $.50 Sock Casing for the 1 $5.00 (green, red) for sensors device displaying signal to user Batteries 9V 1 $2.00 Operational Amplifies voltage signal 6 $15.00 Amplifier from sensors Maxim To generate - 9V 1 $2.00 AD622AN Capacitor Latch Used to keep alarm/LED 1 $.50 CD4043BE on until device is reset PCB Printed circuit 1 $30.00 board 5-input NOR gate Used to determine if a 1 $.50 SN74LS260A signal is on from the 5 TOTAL $136.00 pressure sensors Inverter Invert output 1 $.50 SN74LS04 Electrical Wire Standard wiring 5 feet $10.00 Resistors Standard resistors $2.00 Marketing Factors Condense Circuit – Condensing current circuit on 4-layer PCB increases cost Pressure Sensor Sheet – Instead of specific points, cover entire foot – PolyVinylidine DiFluoride (PVDF) – Increases cost Reliability – Decreasing false positives – Safer design Recommendations Programmable ICs – Integrate amplifier and comparator on one IC PCB technique – Use insulated PCBs to prevent accidental open circuits Multi-functional Speaker – Be able to generate different frequency sounds for different signals Relevant Ethical Issues Current leakage – ‘Leakage Current Tests’ are run on medical related devices for safety – How much current goes through a person’s body when they initially come in contact with the device until the current moves to ground. – There usually will always be some current flow; however, the amount is what is measured here. Prevention – Low current distributes throughout our circuit. Special Thanks Professor Chiang Liu (University of Illinois) Dr. Andrew Reed Dr. Walid Hafez Dr. Raymond Fish ECE Parts Shop Staff Hyesun Park Questions Any Questions?