Library Chair

Overview

The Library Chair is designed to make every library function more efficiently. The library chair design is based on a pressure sensor, which tells whether or not the particular chair is occupied, and then relays the information to a computer, which then compiles information from all of the library chairs. The computer then produces a map of the library and its chairs, and shows which chairs are currently unavailable. This way, each library attendee will know whether or not they will be able to find a seat in the library.

Library Chair Log

Team Members

Josh Zucker

Nick Blenko

Tom Howe

Our wonderful TA, Mo!

And with assistance from Professor Morley

Objectives

Our project's main objective is to create an interface that library go-ers can use to see what seats in the library are available, and which are seated in. We want this product to be low energy, completely solar powered, and to be able to correctly determine if each library chair is occupied, or not.

We have a few minor objectives as well, that reflect our steps in creation. The first objective we are currently working on is how to finalize the circuit we want to use with the pressure sensor, to determine whether or not the library chair is occupied. The objective we have is to determine how we can get the library chair to communicate that it is occupied/unoccupied through radio waves to a processor. Following that, we are going to work on expanding our circuit to be able to operate entirely on solar power. Following that, we want to figure out a way for the processor to communicate the information to some sort of server. Once the server is set up, our next objective is to be able to develop an interactive interface for users attending the library can use.

Challenges

• Finding the best way to communicate information at a low energy level from our circuit in the chair to a processor
• Integrating a pressure detecting circuit with an arduino serving as a function generator and RF communicator
• Learning to use a Raspberry Pi to communicate information to a server
• Setting up a server
• Creating a user interface

Gantt Chart

Budget

• Chair: Cost Varies - (donated by Professor Morley)

• Raspberry Pi: $35.00

https://express.google.com/product/385505035318354406_8630599681660487108_6136318?mall=WashingtonDC&directCheckout=1&utm_source=google_shopping&utm_medium=product_ads&utm_campaign=gsx&dclid=CJ31z4iVq9cCFYIpaQodZkUNkg

• Solar cells: $9.50

(Found on Amazon, but Wiki won't let me post the link to the page because of a spam filter)

• Resistors/other circuitry: $5.00

• Wire: $2.50

• Web Server: $12/Year

https://domains.google/?gclid=Cj0KCQiArYDQBRDoARIsAMR8s_ScLqI_DH4AD7z6oBy_tVey4H-jz4VXtbH8GBIPOwqxhcrwV_F713gaAuZXEALw_wcB&dclid=CJiflsmVq9cCFRYxaQodTZYPtA#/

• Bluehost Account $3.99/Month

https://www.bluehost.com

• RF Link Receiver (433 MHz) $4.95

https://www.sparkfun.com/products/10532

• RF Link Transmitter (433 MHz) $3.95

https://www.sparkfun.com/products/10534

• 2x Arduino Uno - one provided by school, one bought at link below for $27.95

https://www.amazon.com/gp/product/B008GRTSV6/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

Total: $104.84

Building the Circuit

Our circuit is composed of two main parts, an RC circuit and a peak detector. The RC circuit does the actual people detecting. The circuit detects a person because it is fed a square wave with a period roughly equal to four time constants, when someone sits in the circuit they effect the capacitance of it, as the human body has a capacitance of 100-200 pF, and increases the capacitance in the RC circuit, increasing the time constant as well. When the time constant is increased the period of the square wave is not long enough for the capacitor to charge to its peak and so the peak voltage of the circuit is lower when the chair is occupied. The peak detector comes in here to make the measuring the voltage easier. The first part of the peak detector is a diode, which will only let through voltage that is higher than the voltage on the other side of the circuit, therefore if the voltage of the RC circuit is less than the peak voltage it will not be let through. The next element in the peak detector is a parallel RC circuit. In this circuit the capacitor maintains the voltage on the other side of the diode, at the peak voltage, while the resistor slowly drains it, so that when the peak voltage is lowered it is noticed on the other side of the peak detector. Voltage is measured across the parallel RC circuit.

Figure 1:The detection circuit with the peak detector with possible values for capacitances and resistances.

Figure 2:The measured voltage at the peak detector of the above circuit.

Figure 3:A closer view of the voltage at the peak detector in the above circuit.

Group Presentation

Link to the presentation

Interface

To create the interface, we first bought the domain www.librarychair205.com. We then got a third party account at BlueHost, where we could manage our domain. In order to upload code to the domain, it involves creating an FTP account, using Filezilla to upload to that FTP account, using Atom to write code in html so it is compatible with the FTP account, and being able to grab the data from the RaspberryPi server.

Our steps:

• Generate functional HTML code in Atom
• Save the HTML code in index form to be compatible with Firezilla
• Set up the connection between the Firezilla account and the online server's account and IP address
• Upload the FTP file to Bluehost