1. Group 29 JUN SUNG LEE, JAE HYUN KANG
EMPTY SEAT FINDER
Group 29 JUN SUNG LEE, JAE HYUN KANG

2. Introduction

3. Introduction
Time saving way for visitors to find empty seats in a large room
A way to serve seating availability information to guest who has not entered a particular room

4. Objectives
Have a way to distinguish a person from a non-motion object for accurate information
Be able to display the occupation of seats for each row of seats as a visual form for the users
Send the data of unoccupied seat to a personal computer to present the information to visitor who entering the room such as conference hall

5. The Empty Seat Finder

6. Layout of System

7. Block diagram

8. Microcontroller Atmega328p-pu chip
- Input Voltage: 5V
- Crystal Oscillator: 16 MHz
Easily programmable by Arduino codes
Very low power consumption

9. Microcontroller Functions
The main processing unit of the total system
Take the signal values from the sensors to determine whether a seat is taken or not
Handles the taken signal by implemented code and transmits the output signals to other devices
Sends the processed data to the web-server through the Wi-Fi module

10. PIR Sensor
Passive Infrared Sensor (PIR): Used for detection of heat presence. Body heat from human bodies would be used to distinguish humans from inanimate objects. It will generate a 3.3V output when a change in heat radiation is detected. The model used is HC-SR501

11. PIR Sensor Able to adjust the sensitivity of the sensor
-maximum sensing distance : 7m
-minimum sensing distance: 3m
Able to adjust the triggering time for the sensor
-Minimum time : 5s
-Maximum time : 300s

12. PIR Sensor Specifications
Minimum activation distance was too long for our requirements
Provided additional covering inside the lens to decrease the activation distance
Internal reset time of around 3~4 seconds

13. Pressure Sensor
Pressure Sensor: Used for the detection of an object that is occupying a seat. The main portion of this module would be a force sensitive resistor that would change its resistor value depending on the force applied. Constructed out of cheap dissipative foam.

14. Pressure Sensor
Basic Voltage Divider Circuit used for the Pressure Sensor
Regular price of Force Sensitive Resistor(FSR) : around 7$
- we made FSR by ourselves to save price
- get around 1/10 of original cost
- Highly cost efficient!!

15. FSR construction process
Change in dimensions affects resistance values
Small slab dimensions (below 1cm)
-Huge resistance values (50MΩ to over 100MΩ)
-High fluctuations in Resistance values
Large slab dimensions (above 3cm)
-Lower resistance values (less than 10 MΩ)
-Smaller fluctuations leading to more stable resistance
Result : Better resistance if we increase size of dimensions
Our finalized dimensions: 6.5cm x 5.5cm x 3cm

16. FSR construction process
The distance between wires plays a role in determining the resistance of the FSR
Plug wire at least to the middle of the foam slab
We get our expected resistor value within 2cm
Distance between wires
Stand-off resistance (MΩ)
Resistance with pressure(MΩ)
6cm
8.2
3.2
5cm 8
3.4
4cm
7.7
2.8
3cm
6.8
2cm 7
0.9
1cm
6.7
0.8
0.5cm
0.5

17. Pressure Sensor Graph Initial assume fixed resistor = 1MΩ
Finalize fixed resistor =300KΩ

18. Wi-Fi Module ESP8266 ESP-01 - Serial Wi-Fi wireless Transceiver
TCP/IP protocol
Baud Rate: 9600
AT Command through UART
-UART: Serialization from parallel data

19. Wi-Fi Module Functions
The user is able to specify the number of seats through the computer by connecting to the Wi-Fi and assign the number of seats through a simple interface
Gives the ability to transfer data to the status monitor to allow clear visualization of seating information

20. Multiplexer Module for the PIR sensors
two 74LS151 chips – 8 input digital multiplexers
for the Pressure sensors
two 74HC4051 chips - 8-channel analog multiplexers

21. Multiplexing
Assign an address to a certain place rather than taking information from the place itself
Similar to a “pointer” in C language
Selection Bits
Seat 1 2 3 4 5 6 7 8

22. Multiplexer Module Functions
Multiplexing allows us to increase the number of seats drastically by letting us cycle through the seats rather than assigning a single pin for a particular seat
3 selections pins+1 inputs pin ->8 seats VS
A pin for each seat (8 pins) ->8 seats
This leads to an 100% increase for pin availability per seat

23. Multiplexer Module Functions
PIR sensors output 3.3V when triggered and 0V when at rest allowing us easy access to use digital multiplexers
Pressure sensors have a varying voltage output depending on the amount of force applied to the force sensitive resistor
Rather than trying to match the output voltage to the threshold of a digital multiplexer, we used an analog multiplexer to let the microcontroller handle the Pressure sensor output

24. Decoder Module
Two 74HC238 chips - 3 to 8 line decoder

25. Decoder Module Functions
Takes the multiplexed input from the microcontroller and decodes that information to the LED so the user can easily identify the empty seats
Runs with the same selection pins as the multiplexers so that they will achieve the same selection switching time

26. Power Supply and Circuitry
Power Supply: CPSU AC to DC Voltage adapter
-The adapter changes 100~240V input to 4.8~5.2V output
-Maximum output current: 1A
Power Circuitry: 1 AMS LDO -Voltage step down regulator
-The linear regulator changes an 4.8~5.2V input to 3.3V fixed output
- Maximum output current: 1A

27. Power Supply and Circuitry Functions
The adapter is able to connect to any universal household outlet allowing easy connectivity to any location
The 5V current is used to supply power to the multiplexers, decoders, microcontroller and sensors.
The 3.3V current from voltage regulator is used to supply power to the Wi-Fi module

28. Pressure Sensor Output
Logic for Sensors
PIR Sensor Output
Pressure Sensor Output
Human Presence
HIGH
YES
LOW NO
NO(but YES if the PIR sensor had been HIGH for the previous seat check cycle)

29. Pseudo Code for Microcontroller

30. Final Tests and Results
Success:
LED brightness was not terribly defected by up to 1/16 duty cycle applied by multiplexing (no blinking artifacts)
Correct working of the Human detection logic of the microcontroller
Multiplexers and Decoders were able to switch their selection bits at a very fast speed without getting mixed up (1ms interval)
The computer was able to connect to the Wi-Fi and receive the correct information for seat occupation
Able to change the number of seats through the computer

31. Final Tests and Results
Failures:
Microcontroller had difficulty reading in the correct value from the analog multiplexer
Was unable to simulate multiple rows of seats due to data transfer failure of multiple ESP modules
The force sensitive resistor had some fluctuations in its resistance, even at stable conditions the resistance values would continue to change very slowly
Small leaks in the decoder output voltage that would slightly turn on unwanted LED

32. Further Work
Find a better material to gain more consistent values for the force sensitive resistor for more accurate calculations of fixed resistor
Achieve interconnection between ESPs so that more rows can be added to the final design
Design a more comfortable and way of applying the pressure sensor on the seat
Provide an image visualization of the seating arrangements instead of text display

33. Thank you