Objective
Rules
- The Device is built using a microcontroller, a display, LEDs, and a sensor/probe.
- Cannot plugin any devices into a power socket
- Measure mass ranging from 50g to 1kg
- Diameter of objects can be max at 8 cm
- The sensor produces a voltage which varies according to the mass of the object.
- The Device does not require a Wi-Fi/Internet connection at any time during the competition. (Raspberry PI and Mac cannot be connected to WIFI)
- The sensor is constructed from fundamental electronic components such as FSRs, strain gauges, capacitors, resistors, wires, DIP IC chips, and surface mount adapter boards.
- All supporting circuits are assembled on either a solderless or solderable breadboard.
- None of the following are used: preassembled load cells where strain gauges are already wired together or attached to a flexible material, parts taken from such a preassembled load cell, printed circuit boards (except digital display boards), and integrated circuit daughterboards.
- Use of Kits & Digital Fabrication sections of the VASO Constructed Devices Policy are met.
Written Test
- Teams will be given a written test to assess their knowledge of the theories behind the event.
- Teams may use the entire time block to take the written test.
- The written test will be limited to the following topics:
- i. Voltage dividers and the effect of different fixed resistors and the output voltage recorded.
- ii. Types of force sensors and their working principles.
- iii. The relationship between force, stress, strain, and resistance.
- iv. The relationship between force (weight), mass, pressure.
- relationship between mass and weight
- Relationship between force and area
- v. The conversion from analog reading to voltage.
- vi. Theory of LEDs, working principles, and applications.
- This topic on khanacademy has all about semiconductors, transistors, leds etc. https://www.khanacademy.org/science/in-in-class-12th-physics-india/in-in-semiconductors#in-in-band-theory-of-solids
- vii. The process of calibration – working with raw data and determining real world relationships.
- viii. Operational knowledge of basic Device components.
- ix. Topics for State and National Tournaments only:
- (1) Capacitance
- (2) Piezoelectricity
- (3) Wheatstone Bridges (Read up on this electricity unit on Khanacademy
- Wheatstone bridge derivation: https://collegedunia.com/exams/wheatstone-bridge-physics-articleid-39
- (4) Unless otherwise requested, answers must be in metric units with appropriate significant figures.
- (5) While working on the written test teams are not allowed to use any laptops they may have brought with them.
Building blocks
- Breadboard and connector cables (To construct the circuit of leds, Integrated chips and resistors)
- A Force Resistance Sensor (FSR) (Square Force-Sensitive Resistor (FSR) – Alpha MF02A-N-221-A01). The sensor is a variable resistor. The resistance (output) is inversely proportional to the applied force (input).
- Voltage divider, comprising of a fixed resistor and variable resistor (which is the FSR). As force varies the resistance, the drop voltage also changes, which is fed to MCP 3008 (ADC convertor). The output voltage varies based on mass, hence used to create a calibration curve based on variety of masses.
- MCP3008 chip as ADC (Analog to digital convertor). Signal from FSR will be Analog and needs to be converted to a digital format as input to the Raspberry API. For this we need an Analog to Digital convertor. We used MCP3008.
- Mac as the display to view the results. Software: VNC / Remote Desktop/ SSH into the Raspberry PI so we can run the python code and view the results of our code. Refer diagram below which explains the data flow:
Specifications
For more details go here: https://www.raspberrypi.com/documentation/computers/raspberry-pi.html
MCP3008 to Raspberry PI mappings
We used the following mappings from MCP3008 to RaspberryPI. The output from the voltage divider (FSR) was feed into CH0 in MCP.
- MCP3008 VDD -> 3.3V (red)
- MCP3008 VREF -> 3.3V (red)
- MCP3008 AGND -> GND (black)
- MCP3008 CLK -> SCLK (yellow)
- MCP3008 DOUT -> MISO (purple)
- MCP3008 DIN -> MOSI (white)
- MCP3008 CS -> #22 (green)
- MCP3008 DGND -> GND (black)
- Connect one end of FSR to 3.3 V
- Connect second end of FSR to MCP 3008 Cho (i.e. PIN1)
- Connect second end to resistor (for Voltage drop) and the other end of the resistor to Group.
Reference Videos and Links
The video below is a start up tutorial on how to set up a basic circuit using an FSR (Force Sensor), connected to a breadboard with a basic circuit that sends a signal to a PIN on a Raspberry PI. The Raspberry PI runs a Python program to detect the signal as an input to print a message indicating there is pressure on the FSR.
Use Video below to wire an MCP3008 Chip with Raspberry PI and FSR to get variable voltage (Analog to Digital). In you run into an error about missing libraries, follow the instructions here to get the Python libs needed to interface with the MCP 3008 chip here: https://learn.adafruit.com/circuitpython-on-raspberrypi-linux/installing-circuitpython-on-raspberry-pi
References
The link below is from Virginia SciOly team for Detector building. This is a great resource, and also has a video (in a chat format) explaining strategies and rules: https://www.virginiaso.org/events-bc/detector-building
The SciOly Rules can be found here: https://www.soinc.org/sites/default/files/2022-09/Science_Olympiad_Div_C_2023_Rules_Manual_Web_.pdf
A great pdf to learn about how strain guages work: http://elektron.pol.lublin.pl/elekp/ap_notes/ni_an078_strain_gauge_meas.pdf
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