Final Design

The Peripheral Neuropathy Device (PND) consists of six major components:

1. 780-gram binocular load cell

2. 1095 spring steel cantilever spring

3. 0.125-inch diameter stainless steel rod

4. Arduino Micro

5. Texas Instruments INA114-AP instrumental amplifier

6. Monochrome 0.96" OLED graphic display

These six components are housed in a 3D printed chassis (as seen below).

Figure 1. Internals for the PND

    As seen in Figure 1, the stainless steel rod will be in contact with (i.e., "poking") the patient's foot. The stainless steel rod is held in place by a bearing system made of Delrin, which is secured in place when the two parts of the chassis are assembled. A retaining spring and stopper is on the internal end of the rod to maintain contact between the rod and the cantilever beam and is used to prevent any false readings. The cantilever beam is made of 1095 spring steel (thickness of 0.012-inch). The cantilever beam has one end fixed to the load cell and the free end in contact with the stainless steel rod. The cantilever beam does not come into contact with any other part of the chassis, so it can deflect freely. The binocular load cell is connected to the cantilever beam to increase the compliance to the system to improve sensitivity. The load cell is also mounted to the chassis and always stays stationary in the vertical orientation.  

    A summary of the electrical components is as follows. The Arduino Micro acts as the microcontroller that controls the functionality of the device. The Arduino Micro will commands the OLED screen, LED indicator, as well as the user interface. The OLED screen displays the amount of force in grams so the user can easily see how much force is being applied. A Red-Green-Blue (RGB) LED indicator acts as a more visual aid to provide visual understanding while the device is in use. A constant green light shows for a force range from 0 to 5 grams, a constant yellow for 6 to 10 grams, a constant red for 11 to 20 grams, and a blinking red light shows for forces 21 grams or larger.  A patient "freeze" button is also included and used by the patient to trigger the static data display force applied to be recorded by the user. When the patient presses the button, the amount of force applied is "frozen" on the OLED screen, in which the doctor will stop "poking" the foot and record the force being applied on a chart. Once the patient presses the button, the LED light will emit a blue light for three seconds.  

Below is a CAD of the Final Design.

Figure 2. CAD of the Final Design

    After describing the components of the device, it is important to know how to use the PND. Below is the flow chart of the PND. 

Figure 3.  Flow Chart of PND

    The flow chart in Figure 3 tells the user what they will expect once the device is turned on. The user will first be welcomed with a "Welcome!" on the screen. Once the screen clears, the screen will display a force output, which will display "0 grams." This should be calibrated but the user should confirm that the OLED display is properly displaying zero. The doctor will then slowly apply force to the first location (big toe) on the patient's right foot. Once the patient detects sensation, the patient will press the "freeze" button thus emitting a blue light on the LED. The user notices that the force has been felt and then will continue to record the data, wait three seconds, and verify the re-calibration. Then, the user will repeat the test on the remaining eight points on the right foot before proceeding onto the left foot.  

During preliminary testing, it was found that correlation between monofilament results and peripheral neuropathy device was high with an average test time of 2 minutes and 6 seconds. Data collected from the tests shows the locations on the foot where the monofilament was not felt when the force applied was greater than 10 grams, demonstrating higher quality information than the current test. A case study shows when tested one patient 10 times, averages of 20.45±7.84g, 22.36±10.1g, and 11.36±8.34g were found where peripheral neuropathy was found to be present and correlated with inability to detect the monofilament test. For samples that showed no peripheral neuropathy, averages such as 3.18±1.11g and 4.54±1.23g also correlated with the ability to detect the monofilament test. The accuracy of the device showed small error where neuropathy was not present with a standard deviation as low as ±1.1g and high error where neuropathy is present with standard deviation up to ±10.1g, proving the functionality of the device and proof of concept.