Final Project

BMI Calculator

The BMI Calculator is an interactive device which designed to measure a person’s weight and height and then instantly compute their Body Mass Index (BMI). Its goal is to make health monitoring quick, accessible, and user-friendly for many people.

Why I chose this project?

Body Mass Index (BMI) is one of the simplest measurements used globally to assess the structure of a person's body. It gives an estimate of whether a person is underweight, normal weight, overweight, or obese. However, taking BMI traditionally involves the use of various devices — a scale for weight and tape or stadiometer for length — and manually calculating.

With the BMI Calculator, I aimed to design one, self-contained device that allows individuals to easily and rapidly measure their weight and height and instantly computes the BMI and shows the output clearly. It also Offers a simple user interface, allowing it to be used in schools, gyms, clinics, or even at home.

Project goal

My goal is to build, construct, and code an integrated system that:

Final project draft

1. List of materials

Items Quantity Price/unit Total price Link
Load cell (200kg) 1 39.00 $ 39.00 $ amazon.com
HX711 Load Cell Amplifier 1 3.50 $ 3.50 $ amazon.com
HC-SR04 Ultrasonic Sensor 3 3.50 $ 3.50 $ amazon.com
9mm MDF board 1 25.00 $ 25.00 $ Local hardware store
40x40 metal tube 1 6.00 $ 6.00 $ Local hardware store
LCD Screen 1 9.96 $ 9.96 $ amazon.com
Keypad (4x4) 1 2.50 $ 2.50 $ amazon.com
Total 89.46 $

2. Final project design

I started with the design of load cell. Since the structure will revolve around it, I am using SolidWorks multibody method to make the process seamless.

Final project design

I then designed (metal) frame around the load cell.

Final project design

Since the top and bottom frame must not touch each other, however it is not necessary to keep them far apart. Therefore, I reduced the distance between the. I used move mody method.

Final project design

At the bottom frame, I extended it by adding a frame to support the vertical stand.

Final project design

I then added vertical stand of 2.1m tall.

Final project design

Since this stand is tall, I splitted it into 3 sections. This not only easy the assembly, it also ease its packaging and transportation

Final project design

I then added support structure inside. This will also guide me during assembly.

Final project design

I then added cutout for screen as well as that of Ultrasonic Sensor

Final project design

Cutting parts on CNC Machine

I imported all dxf files into VCurve and rearranged them accordingly.

Final project, cutting

Since some parts are really small, I added tabs to hold them. This is to avoid parts from displacing which may break tool as well faults (inaccuracy) of output.

Final project, cutting

CNC done cutting

Final project, cutting

Angle cutting

Sone parts needed to be cut on angle. Therefore, I used circular saw to cut them.

Welding frame

For welding, I cut all pieces sized according to the dimensions.

Frame welding

I cut the shape (template) of frame from MDF to ease the alignment.

Frame welding Frame welding

3D Printing of some parts

I started with ultrasonic holder. I used ultimaker cura for slicing.

3D Printing

Printing done. Success!

3D Printing

Next I printed screen holder. This also hold keypad, power button and pcb board.

3D Printing

In other to make assembly and disassembly of sections doable, I added nuts holded by 3D printed parts. I used glue for their assembly.

Assembly Assembly

Assembly of structure

Assembly was straight forward since I tested fitting before.

Assembly

Electronic design

To design PCB, I used KCad

PCB design PCB design PCB design

PCB Milling

To start off milling, I used modsproject.org to generate gcode

PCB design PCB design

Then I used PCB milling machine to print it. I used openbuilder Program for machine control.

PCB design PCB design PCB design

Result

PCB design

Soldering

I soldered EPS-32S microcontroller, extension pins and other components.

PCB design

I then soldered HX711 Load Cell Amplifier

PCB design

At each wire, I also soldered jump wires to make I can plug and unplug divices easily.

PCB design

Assembly all sections

I started by assembly load cell with the stand. This is one of the crucial process. The load cell need to be as rigid as possible relative to its frame.

I followed up with other sections

PCB design

I then used bolts for tightening. I also inserted load cell wire along the way.

PCB design

Next I assembled the top part with Ultrasonic Sensor already installed. After I added its cover.

PCB design

Programing

I used arduino IDE for programming

PCB design PCB design

Note: Code I used can be found at the bottom of this page in download section.

Calibration

One challenge I faced was to calibrate the load cell. Previously it was reading offscale values.

Therefore, I used kitcken scale to measure few items accurately. Then I used them to adjust scale factor (calibrate load cell).

PCB design PCB design

At the bottom, I added 3D printed stand. Because of bolts and nuts petrouding undeerneth, the entire structure was not standing upright.

PCB design

Testing

I then assembled everything together and then connected to power. The power is 5V.

PCB design

Powering on machine.

Machine measuring one of my collegue

Download files

There are files including CAD file, pcb and arduino code I used.

CAD files

PCB Design

Arduino code