Difference between revisions of "Library Chair"
| Line 39: | Line 39: | ||
==Building the Circuit== | ==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. | ||
[[File:Chaircircuitwithvalues1.png|thumb|'''Figure 1:'''The detection circuit with the peak detector with possible values for capacitances and resistances.]] | [[File:Chaircircuitwithvalues1.png|thumb|'''Figure 1:'''The detection circuit with the peak detector with possible values for capacitances and resistances.]] | ||
[[File:Chairpdvoltage1.png|thumb|'''Figure 2:'''The measured voltage at the peak detector of the above circuit.]] | [[File:Chairpdvoltage1.png|thumb|'''Figure 2:'''The measured voltage at the peak detector of the above circuit.]] | ||
Revision as of 21:09, 11 October 2017
Contents
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.
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
- 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)
- TI MSP 430: $30.03 (donated by Professor Morley)
- Raspberry Pi: $25.00
- Solar panels: $6.95
- Resistors/other circuitry: $5.00
- Web Server: $0-$5/Month
Total: $66.98+
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.
