Library Chair Log

Group Members

• Josh Zucker
• Tom Howe
• Nick Blenko

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

Josh

• This week I finished modeling the detection circuit for the chair and am now figuring out what values of capacitance and resistance I want to use to best detect someone sitting in the chair. I want to makes 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.

The detection circuit without values for capacitance and resistance

Tom

• This week I compiled all of our progress we have made so far and updated our wiki page for the Library Chair. I also wrote a description of the circuit that Josh had put together, and am currently working on how I can upload images on to the wiki to create a figure and summarize the progress we have made on it thus far. In the coming days, I want to create more comprehensive description of the circuit and how it works, and include a diagram (stole this idea from another wiki page) of how we will be delegating out our work for the semester.

Nick

Week of October 2

Josh

Tom

Nick

Week of October 9

Josh

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