Library Chair Log
Contents
Group Members
- Josh Zucker
- Tom Howe
- Nick Blenko
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.
Week of September 4
This week we began thinking of how we were going to approach the concept of building the library chair. Our original concept is a cushion on top of a weight sensor which is hooked up to an Arduino and Bluetooth transmitter which will transmit to a raspberry pi that will run the server and website where the data will be displayed. Each chair will send a 1 or 0 every minute to update the server with the chair either being open or occupied.
Week of September 11
This week we met with Professor Robert Morley who had begun the project earlier. Morley had a working prototype of the chair in his office. He, instead of a weight sensor, used an RC circuit and square wave to detect whether or not someone was sitting in the chair. When someone would sit in the chair their body would increase the capacitance of the capacitor and decrease the impedance of the circuit causing peak voltage in the circuit to drop, this could be measured with an Analog/Digital converter in an MCU and transmitted via radio signal. Morley gave us an MCU with a radio transmitter built in to begin working on.
Week of September 18
This week we met with Morley again to better understand the circuit he was using to measure the peak voltage. He showed us the idea of a peak detector; a circuit with a diode, capacitor, and resistor in it. The diode would only allow voltage through if it was greater than the voltage on the other side of the diode, the capacitor maintained voltage in the circuit so only peaks would be measured in the peak detector, and the resistor would drain current so that if there was a reduction in voltage, for example when someone would sit, the peak detector would be able to pick that up. This circuit makes measuring peak voltage much easier and we thus will not have to worry about measuring voltage on a part of the wave that is not the peak. We began modeling the circuit on LTspice and will hopefully begin prototyping soon. We also looked at potential problems we may face when getting the chairs to communicate with the processor, and then getting that information loaded onto a computer that can produce an interface for users to see which chairs are available. Our primary means of communicating to the server is currently a radio, and then we plan to use a Raspberry Pi to get that information into a computer. We also looked into other alternatives we may use if we face problems with radio transmission. We thought that bluetooth could maybe be a feasible route, and looked into the puck.js, which is a low energy programmable bluetooth device. However, we are trying to work with radio for the time being. Finally, we got to work examining the low power MSP430 microcontroller that Professor Morley gave us. It came with a radio antennae, and connects through a USB port via a flash emulator. We found the correct IDE to use with the microcontroller (we think), and started exploring how to program it, getting simple "Hello World" type programs to run on it. We will be writing code in C, which we have extensive experience working with having taken CSE 132 in the last year. The next step is to write code that takes readings from the circuit attached to the chair, and discerns whether or not someone is sitting in it.
Week of September 25
This week we finished modeling the detection circuit for the chair and are now figuring out what values of capacitance and resistance to use in order to best detect someone sitting in the chair. We want to make the resistance relatively high and the capacitance relatively low in order to create a stable circuit that will easily detect someone. At the same time, if resistance is too high there won't be enough current flowing into the peak detector and if capacitance is too low the chair could be triggered by somebody walking by.
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We also continued familiarizing ourselves with the TI MSP430-specific IDE, and investigated potential alternatives to RC circuitry for pressure sensing, including sparkfun (arduino) sensors, in case the RC circuit turns out to be too finnicky. Finally, we compiled all of the progress we have made thus far and updated our wiki page for the Library Chair. We also wrote a description of the circuit that we put together, and are currently working on how to upload images onto the wiki. In the coming days, we want to create a more comprehensive description of the circuit and how it works, and upload our Gantt chart of how we will divide our labor in the coming weeks and months.
Week of October 2
This week each of us continued working on our individual parts of the project. We continued physically prototyping the circuit and testing for ideal resistances and capacitances for the circuit and are beginning to test the effect of proximity to a person on the peak voltage in the circuit. We also continued working on the IDE for the TI microprocessor, getting it to run the "hello world" program and beginning to work on the code for the square wave generator and voltmeter. We also continued to work on creating a server with a raspberry pi.
Week of October 9
Josh
- Worked on math behind calculating circuit element values (1.5 hours 10/9)
- Continued prototyping circuit and incorporated calculated values (2 hours 10/11)
Tom
Nick
Week of October 16
Josh
Tom
Nick
Week of October 23
Josh
Tom
Nick
Week of October 30
Josh
Tom
Nick
Week of November 6
Josh
Tom
Nick
Week of November 13
Josh
Tom
Nick
Week of November 20
Josh
Tom
Nick
