Simulation of Flex sensor circuitry

[TheProjectsGuy]

Task priority: HIGH

Task description

Simulation of Flex sensor circuitry on MATLAB. References issue #15 (Main task list for @TheProjectsGuy)

Person assigned: @TheProjectsGuy

Deadline: Sunday, 5^th February 2019

Must Haves

Get a simulation up and running, giving useful values as proof of concept.

• [x] MATLAB Simulink Simulation
  • [x] Find the correct values of variables to be used
• [x] Import to other versions (R2016a) and documentation
• [x] Shift changes to dev branch through a pull request

Extras

Things that could be worked on after the must haves are finished.

• [x] Interactive mode to change all the values and see things easily

Attach all results to this issue as well, for documentation purposes

[TheProjectsGuy]

Tests done on the 2.2'' flex sensor

Reasons for failure

1. Unavailability of exact resistance values

   MATLAB Trial 1 !! Test Failed !! :warning:

   Edited the default configurations for the flex sensor and stored in the file Flex_Sensor_final_circuitry.slx. The default values for resistors was decided to be 1.5 kΩ + 180 Ω for input and 22 kΩ for feedback. The results are as follows:

   • Circuit design in simulation
   • The output designs are as follows
     • Vout: Output voltage of instrumentation amplifier: 0.459 V to 4.97 V (difference of 4.51 V)
     • Raw output: Output of voltage divider (wheatstone bridge): 0.0351 V to 0.38 V (difference of 0.345 V)
     • Amplification factor = 13.095

Parts needed :warning: :name_badge:

Circuitry

• [ ] Flex sensor 2.2''
• [ ] Resistors
  • For instrumentation amplifier
    • [ ] 1.5 kΩ resistors (x 2)
    • [ ] 180 Ω resistors (x 2)
    • [ ] 22 kΩ resistors (x 2)
  • For the wheatstone bridge
    • [ ] 80 kΩ resistors (x 2) for the upper arms
    • [ ] 70 kΩ resistor (x 1) for the reference arm (lower resistor)
• [ ] Op-Amps (x 3) for the instrumentation amplifier construction
• [ ] Breadboard and jumper wires
• [ ] Arduino and multimeter for programming and debugging

[TheProjectsGuy]

Simulation solved

[TheProjectsGuy]

The resistance values will have to be tweaked because of limited availability, the available resistors are as shown below Suggested to make modifications ASAP, deadline shifted to Tuesday, 5^th February 2019...

[TheProjectsGuy]

Tests done on the 2.2'' flex sensor

MATLAB Trial 2 :warning: TEST FAILED

Edited the default configurations for the flex sensor and stored in the file FlexSensor_Customizable_2in2.slx. The default values for resistors was decided to be:

• 100 kΩ for upper arm and 68 kΩ for lower arm at the wheatstone bridge.
• 8.2 kΩ for input and 100 kΩ for feedback, giving a gain of 12.195 at the instrumentation amplifier.

The results are as follows:

• Circuit design in simulation
• The output designs are as follows
  • Vout: Output voltage of instrumentation amplifier: 5.03 V to 0.844 V (difference of 4.18 V)
  • Raw output: Output of voltage divider (wheatstone bridge): 0.0692 V to 0.4121 V (difference of 0.3429 V)

Parts needed :warning:

Circuitry

:warning: :warning: Issue outdated, please skip this list :warning: :warning:

• [ ] Flex sensor 2.2''
• [ ] Resistors
  • For instrumentation amplifier
    • [ ] 8.2 kΩ resistors (x 2)
    • [ ] 100 kΩ resistors (x 2)
  • For the wheatstone bridge
    • [ ] 100 kΩ resistors (x 2) for the upper arms
    • [ ] 68 kΩ resistor (x 1) for the reference arm (lower resistor)
• [ ] Op-Amps (x 3) for the instrumentation amplifier construction
• [ ] Breadboard and jumper wires
• [ ] Arduino and multimeter for programming and debugging
• [ ] 2 Position Male FCI connectors

[TheProjectsGuy]

Flex Sensor testing

Flex Sensor length	Finger(s)	Resistance at full inward bend	Resistance at full outward flex	Comments
2.2in	Thumb	75 kΩ	130 kΩ	Flex sensor has to be used with translucent side facing outwards, hence values are reversed. Suggested to change the position on wheatstone bridge
4.5in	All four 3 joint fingers	25 kΩ	8.5 kΩ	Flex sensor has to be used with black line facing inwards. Suggested to maintain the position on the wheatstone bridge

Since the flex sensor readings are different, the resistance values will have to be tweaked along with a factor of safety (to avoid out of bounds cases). It's suggested to use:

• 1 kΩ factor of safety for 4.5in flex sensors
• 2 kΩ factor of safety for 2.2in flex sensors

Thus, the ranges are:

• 2.2in: 73 kΩ to 132 kΩ.
• 4.5in: 26 kΩ to 7.5 kΩ

Course of action

• [x] Abondon version 1
  • Test results: :warning: Test failed :warning:
  • Test output
    • Make versatile circuitry
• [x] Start Version 2

These will keep everything in bound... Task list:

• [x] Voltage divider network for both the flex sensor types
• [x] Determine the constant reference voltage arm to be used for the wheatstone bridge
• [x] New resistance values to be found
• [x] Documentation update

[TheProjectsGuy]

Remaining task list:

CAD Files

Using Eagle, create the following CAD files

• [x] CAD for 2.2" flex sensor
• [x] CAD for 4.5" flex sensor
• [x] CAD for entire hand using the analog MUX
• [x] Bill of materials - BOM

[TheProjectsGuy]

Issue solved on Saturday, 16^th February 2019. Proceeding to the next issue in hand