Sound powered phones/Howard Community College/Fall 2011/550 EPC

Electronic Sections Expected

Problem Statement

Build a sound powered phone system for the classroom

Team Members

Put each team members name here with links to their personal page here. Real names do not have to be used.

Epcole

Summary

This project was to build a sound powered phone system that could be used in the classroom. At first we were looking for vendors to buy some parts but after very little success, we started to work on how to build a system.

Poster

To the right is the basic idea behind the sound powered phone's microphone. Its very similar to the design of a speaker right now but I think its a good starting point.

S P P Reciever - side

Story

We actually stumbled upon this project while trying to fix a broken speaker. We were looking at how the speaker works and noted that it could work in reverse and the sound powered phone came up. The speaker's coil magnetizes and is attracted to the base of the speaker when current flows through it. The coil can also send out a voltage when it cuts through the magnetic field and when that voltage is sent to another speaker, it causes that speaker to move. We wanted to build a system for the classroom from old scrap parts. The first part was just to see the speaker's output when used as a microphone. The small speaker produced about a 2mV peak which is pretty low. Not sure if its enough to generate sound on the other end but that hasn't been tested yet. Finding parts to sound powered phones proved to be very difficult so we decided to start working towards building one from scratch. At this point, getting a coil with enough inductance to produce a decent voltage with minimal movement while not being too bulky is the first step.

Decision List

Find Sound Powered Phone Parts
Find detailed drawings and information on how a sound powered phone is constructed
Search for parts that can be used in building a sound powered phone system
Design a test microphone as a starting point

Material List

The materials list was pretty short since most of the parts needed were taken from used speakers.

36AWG magnet wire
Headphones

Software List

No software was needed for this project

Time

The initial search for parts consumed most of the first few weeks with a few weekly hours spent on messing with speakers. Over the last week of the project I came up with a design for the microphone.

Tutorials

http://crystalradio.net/soundpowered/insideelements/index.shtml has a drawing and photos of an old sound powered phone. The system proposed would be based on the information on this page.

Next Steps

A good starting point would be to check out the link to the crystalradio page and see how the sound powered phone is constructed. Right now the first thing to do is to build a coil with a good inductance value without being too bulky. A wire that is very thin would allow for much more turns in the coil. Another step is to find a material that can be used as a diaphragm. Latex has been suggested but I'm skeptical because of its strength.

Subjective Critera

While reading these sections, practicing engineers are building up the following impressions about the document. So the following categories are more subjective:

Repeatablitly

Is there enough detail to repeat the work?

Integrity

Proving something doesn't exist or doesn't work usually requires exhaustion. Simply saying "it can not be done" is like challenging a pro basketball player (engineer) to one-on-one basketball (find a solution). It does not inspire respect. All the different ways respect is created can be found throughout the wikibook General Engineering Introduction.