Piezoresistor Sensor Testing (4.5 hrs): Together with Josh, I helped test our current piezoresistor model (A301) to determine if it was viable for our project goals and use cases. While Josh built the circuit (and testing environment) and set up the STM32 ADC, I calculated the AC and DC gain of the amplifier to assist us in adjusting the values of the supply voltage (Vdd), reference voltage (Vref), and the feedback resistor (Rf) to attain an ideal range of outputs that we can use to accurately track force placed on the piezoresistor sensor. Currently, we have found that the following values yield the following output range: Vdd = 2V, Vref = -2V, Rf = 220 kOhm, C1 = 47 pF, Output Range = (approximately) 10mV – 2000mV. Further testing with standardized weights will be conducted to further determine accuracy and initial calibration of the sensor. We have placed an order for the remaining sensors following our test results.
Android App Development (4h): I created a template for our CLIMB mobile app in Android Studio as well as the landing page, however I have not implemented the login page yet. I have not programmed in Kotlin before, so I have spent considerable time learning it over the past several weeks, but I have plenty of experience with similar programming languages and have no reason to believe it will cause any delay in the development of the rest of the app.
Biomechanics Research (3h): I conducted biomechanics research on the physiological relationship between the A2 and A4 pulleys and the respective tendons that they are responsible for. I determined that the initial placement of our sensors will likely suffice for prevention of pulley injuries. Additionally, I have found that typical A2 pulleys can generally hold up to 380N to 400N of force, so for safety and testing reasons we will likely use approximately 75% of that value (85.4 lbs to 90.0 lbs) as our alarm threshold for the A2 pulley sensor during integration testing. In our piezoresistor testing, we have found that bending of the sensor does not appear to affect the accuracy of the force readings, and as a result this should not impact our intended force sensor placement. Additionally, the A301 sensor data sheet states that the sensor can withstand forces up to 4400 N (1000 lb), so it should be more than able to handle the range of forces we intend to measure with our product.
Mandatory Lab Meetings (2.5h): Met with the professor and TA and received valuable feedback about our presentation and project implementation. One especially valuable piece of information that I received from the professor was to begin thinking about amplifier circuits as well as bridge circuits while tuning the output of our piezoresistor. After the meeting I researched the Wheatstone Bridge design of a piezoresistor which helped me gain an understanding of how it would fit into our circuit as well as how the piezoresistor worked internally.
Progress
My progress is currently on schedule according to our Gantt chart. I believe learning Kotlin for app development will take some time and will allot additional time as needed for this task in next week’s schedule.
next week tasks & goals
Android App Development: Create sign-in page for the app, ideally with OAuth google account sign-in. Additionally, some time will be spent learning Kotlin and additional features in Android Studio.
Additional Piezoelectric Sensor Testing: Now that we have determined that we will be moving forward with the A301 sensor, we will test the sensor with standardized weights to begin calibration of the sensor and determine corresponding force readings with voltage outputs.
