Monitoring System Design​​

A project log for Économique Bionic Leg System

The project emphasizes on providing value for money by using a bionic leg for sprinters embedded with smart monitoring system.

premj20PremJ20 08/29/2017 at 03:580 Comments

In our system design the components used are:


This flex sensor is a variable resistor like no other. The resistance of the flex sensor increases as the body of the component bends so on one side of the sensor is printed with a polymer ink that has conductive particles embedded in it.
Left flat, these sensors will look like a 30kΩ resistor. As it bends, the resistance between the two terminals will increase to as much as 70kΩ at a 90° angle.
By combining the flex sensor with a static resistor to create a voltage divider, you can produce a variable voltage that can be read by a microcontroller’s analog-to-digital converter.

                                                         Flex sensor circuit

In our project the flex sensor is used to measure the flex angle between knee joint and lower leg.


An accelerometer is an apparatus used for measuring acceleration or deceleration - that is, the rate of increase or decrease in the velocity of a moving object. Accelerometers are used to measure the efficiency of the braking systems on road and rail vehicles; those used in aircraft and spacecraft can determine accelerations in several directions simultaneously. The measurement of acceleration or one of its derivative properties such as vibration, shock, or tilt . In our project a 3 axis accelerometer is used i.e ADXL335. 

 The ADXL335 is a small, thin, low power, complete 3-axis accelerometer with signal conditioned voltage outputs. The product measures acceleration with a minimum full-scale range of ±3 g. It can measure the static acceleration of gravity in tiltsensing applications, as well as dynamic acceleration resulting from motion, shock, or vibration.

The user selects the bandwidth of the accelerometer using the CX, CY, and CZcapacitors at the XOUT, YOUT, and ZOUT pins. Bandwidths can be selected to suit the application, with a range of 0.5 Hz to 1600 Hz for X and Y axes, and a range of 0.5 Hz to 550 Hz for the Z axis.

The ADXL335 is available in a small, low profile, 4 mm × 4 mm × 1.45 mm, 16-lead, plastic lead frame chip scale package (LFCSP_LQ).

                                                                ADXL 335

                                                 ADXL 335 circuit diagram

In our project the accelerometer is used to measure the acceleration or movements of the lower leg. Due to the limitations of technological boundaries and cost the 3 axis accelerometer is used. In the future a high precision accelerometer will be taken to consideration.


The Photon is a microcontroller, which is a small, low-cost, low-power computer that can run a single application. The microcontroller runs the software and sends signals to the Photon .

Microcontrollers are particularly good at controlling things. They have a set of pins that are called GPIO (General Purpose Input and Output) pins, or I/O pins. They can be hooked to sensors or buttons to listen to the world, or they can be hooked to lights and motors to act upon the world. These microcontroller’s pins have been directly connected to the headers on the sides of the Photon so you can easily access them; specifically, the pins labeled D0 to D7 and A0 to A7 are hooked directly to the microcontroller’s GPIO pins.

The microcontroller can also communicate with other chips using common protocols like Serial (also called UART), SPI, or I2C (also called Wire). You can then make the Photon more powerful by connecting it to special-purpose chips like motor drivers or shift registers. Sometimes we’ll wrap up these chips on a Shield, an accessory to the Photon that makes it easy to extend the Photon.

The Photon also has a Wi-Fi module, which connects it to your local Wi-Fi network in the same way that your computer or smartphone might connect to a Wi-Fi network. The Photon is programmed to stay connected to the internet by default, so long as it can find and connect to a network.

When the Photon connects to the internet, it establishes a connection to the Particle Cloud. By connecting to the Cloud, the Photon becomes accessible from anywhere through a simple REST API. This API is designed to make it very easy to interface with the Photon through a web app or mobile app in a secure, private way, so that only you and those you trust can access the Photon.

                                                     Particle Photon(both sides)

There are two buttons on the Photon: the RESET button (when holding the Photon with its USB-port to the top, it’s the button on the right) and the MODE button (on the left).

The RESET button will put the Photon in a hard reset, effectively depowering and repowering the microcontroller. This is a good way to restart the application that you’ve downloaded onto the Photon.

The MODE button serves three functions:

                                                Particle Photon schematics


The Photon has 24 pins that you can connect a circuit to. These pins are:

In our project the Particle Photon is used to obtain the sensor data and process them and send to the data to cloud/mobile app (ThinkSpeak Cloud) for easy visualization