People with sitting jobs in offices often end up having back pain and other bone related issues due to their improper seating posture. To address this issue, a modular cushion is made with flex sensors embedded in it. The cushion is also connected to a computer wirelessly via Bluetooth. When a person slouches, the computer goes into the sleep mode and wakes up only when the person sits with proper seating posture.
Step 1: Components Required:
- Arduino UNO R3 x 1
- USB cable x 1
- HC- 05 Bluetooth module x 1
- Resistor- 24.6K ohms x 2
- Resistor 1K ohms x 1
- Resistor 470 ohms x 1
- PN2222A Transistor x 1
- Breadboard x 1
- Jumper Wires Male - Male (M-M) x 20
- Jumper Wires Male - Fe-Male (M-F) x 20
Step 2: Connecting Flex Sensors to the Arduino UNO
Flex sensors are sensors that changes its resistance depending upon the extent to which it is flexed. The resistance changes in the range of KΩ.
- Connect an M-M jumper wire from the 5V pin of Arduino to the breadboard (5V line).
- Connect an M-M jumper wire from the GND pin of the Arduino to the breadboard (GND line).
- Attach M-F jumper wires (/solder) on each pins of both flex sensors.
- Connect one pin each of each flex sensors to the 5V line.
- Connect the other pins of both flex sensors separately on breadboard.
Step 3: Connecting Voltage Divider Circuit
24.6KΩ Fixed Resistor:
This fixed resistor is used to build a voltage divider circuit. Using the correct resistor aids in obtaining the required sensitivity needed for this project. (If exact 24.6KΩ resistor is not available, three 8.2KΩ resistors can be connected in series to obtain the same resistance)
- Connect one end of the 24.6Kohms resistor on the GND line and the other end to flex sensor 1.
- Repeat the above step for flex sensor 2.
- Connect an M-M jumper wire from the junction of 24.6K ohms resistor and flex sensor 1 to Pin A0 of the Arduino UNO.
- Connect an M-M jumper wire from the junction of 24.6K ohms resistor and flex sensor 2 to Pin A1 of the Arduino UNO.
Step 4: Connecting the Transistor
PN2222A is an NPN BJT (Bipolar Junction Transistor). It has three pins i.e., Emitter, Base and Collector. The transistor acts like a switch. When the Base pin is triggered, Emitter and Collector pins are shorted. To reduce the voltage on the Base pin, a 1Kohm resistor is used.
- Place the PN2222A transistor on the breadboard.
- Connect an M-M jumper wire from Pin 13 of the Arduino UNO to 1Kohm resistor placed on the breadboard.
- Connect the other end of the 1Kohm resistor to the base of the transistor.
- Connect an M-M jumper wire from the GND line of the breadboard to the Emitter of the transistor
- Connect a 470 ohms resistor from the 5V line to the Collector of the transistor.
Step 5: Connecting the HC-05 Module
HC-05 Bluetooth Module:
It is a wireless communication module that transmits data serially. Out of the six pins that comes with general break out board, only 4 pins are used. VCC pin of HC-05 is connected to +5V while GND pin is connected to GND of the microcontroller. RX pin refers to receiver and TX pin refers to transmitter. These pins are used for communication between the Bluetooth and the microcontroller.
Note: HC-06 Bluetooth modules can also be used for this project instead of HC-05.
- Connect an M-F jumper wire from the VCC pin of the Bluetooth to the 5V line of the breadboard.
- Connect an M-F jumper wire from the GND pin of the Bluetooth to the Collector of the breadboard.
Step 6: Upload the Arduino Sketch
Step 7: Download and Install the BtProx Software
- Download the zip file.
- Unzip the file.
- Open btprox.exe file.
- Pair the HC-05 with your laptop/computer
- Select the HC-05 device in the software
- Set the time after which the laptop/ computer should go into sleep mode.
- Click 'Start'.
For more detailed instructions, please refer to http://btprox.sourceforge.net/