Telephone Set Function 4. To convert voice frequencies to electrical signals that can be transmitted

In my last few legacy Public Switched Telephone Network (PSTN) posts, I covered pulse or rotary dial service, dual tone multi frequency (DTMF) dialing service and what makes a telephone ring. In this post let's look at microphones and speakers.

A telephone converts voice frequencies to electrical signals and electrical signals back to voice frequencies using basic microphone transmitter and speaker theory and application. 

Transmitters

A telephone transmitter is built into the handset of the phone and is responsible for converting sound waves into electrical signals that can be transmitted.

Telephone Carbon Granule Transmitter

Carbon granule transmitters are still common in wired home phones. Sound travels in waves that are actually variations in air pressure. Some of these waves enter the mouthpiece and cause a diaphragm in the transmitter microphone to vibrate back and forth. These vibrations put either more or less pressure on carbon granules in the base of the microphone. If more pressure is applied, the granules pack more tightly and conduct electricity more efficiently. Inversely, in between the waves the granules unpack and do not conduct as well. Voltage is applied across the electrical contacts and the varying amounts of resistance caused by the carbon granules in the microphone cause varying amounts of current to flow. This current variation is an electrical representation of the sound waves (voice=analog signal) entering the microphone. 

In addition to carbon granule transmitters many modern telephones use dynamic transmitters that function by moving a coil of wire inside a magnetic field to produce an electrical current in response to soundwaves or electret transmitters, also known as condenser microphones, which use a capacitor for a transducer and generally contain an amplifier circuit. 

Receivers

The telephone handset receiver is just a simple speaker. It performs the opposite function of the transmitter in that it takes the incoming electrical signal and converts it to sound waves that can be heard by the listener. 

Simple Speaker Diagram

The incoming electrical signal flows through a magnetic coil in the speaker. The magnetic field surrounding the coil changes in conjunction with the changing current flowing through the coil. This changing magnetic field causes a cone in the speaker to vibrate. These vibrations create air pressure waves forming sound.

In my next legacy PSTN post I'll describe how some additional telephone features work.

Early Fall Walk Around the STCC Technology Park

I took a quick walk at lunch time today around the STCC Technology Park. The Tech Park is part of Springfield Technical Community College and located directly across the street from the main campus. Our NSF funded National Center for Information and Communications Technologies is located in the Scibelli Enterprise Center building in the Tech Park. Lots of cool technology going on in the Tech Park - things like photovoltaics, electric cars and of course Information Technology and Communications! Here's some of the pics I took today.

gordonfsnyder's photostream on Flickr.


A great place to locate a business and work!

Telephone Set Function 3 - To provide a way for the telephone company to indicate that a call is coming in or ringing

In my last two legacy Public Switched Telephone Network (PSTN) posts I covered pulse or rotary dial service along with dual tone multi frequency (DTMF) dialing service. In this post let's look at what makes a telephone ring.

When the user begins dialing the phone each sequenced number is stored in the central office computerized switch at the Local Exchange Carrier (LEC) Central Office (CO) and analyzed. The first three digits determine if the call is local or long distance. If the call is local, the switch determines if it can complete the call itself or the call needs to be forwarded to another local LEC CO that handles that telephone number. If the call is long distance, the call needs to be forwarded to the customer's long distance carrier.

Once the call destination is determined a switch on the receiving end sends a repeating 90 Vrms 20 Hz ringing signal (on for 2 seconds with a 4 second pause) called a ring or alerting signal to the receiving phone causing it to ring.

Ring or Alerting Signal

Notice the ringing signal has an inaudible frequency of 20 Hz - this is why different phones can have different ring styles.

At the same time, a ring back signal that is a mix of 440Hz and 480Hz is sent back to the caller. This signal is on for 2 seconds and off for 4 seconds and indicates that the phone being dialed is ringing. When the receiver picks up the handset the telephone goes off-hook.  The switch hook on the receiving phone closes, current flows and the CO switches turn off the ringing signals.

Facebook Will Need Its Own Operating System

Gabby came home today for a little while and she had her Chromebook with her. If you haven't seen one yet - it's a pretty cool little notebook running Google's Chrome operating system. It boots up in about three seconds and has a battery that lasts over 8 hours. Everything is stored in the cloud so everything is accessible with a web connection. Pretty nice for a first generation device.

It got me thinking - Facebook does not have a mobile operating system (or any operating system for that matter). Apple does, Microsoft does and Google now has more than one. Poking around on the web I found an interesting report from ABI Research titled Mobile Social Networking. Here's some quotes from that report:

The number of people accessing social networks from mobile phones will exceed 550 million in 2011, and that figure will more than triple to over 1.7 billion by the end of 2016. 

For Facebook, the growing importance of mobile is both an opportunity and a serious strategic challenge. On one hand, mobile allows the world’s leading social network to engage with millions of new consumers, but on the other hand its ability to make money from mobile users remains untested. 

Senior analyst Aapo Markkanen is also quoted in the report saying, "A huge problem for Facebook is that while on the web it is a platform, on mobile it’s just another application. To strengthen its hand in the short term we expect Facebook to aggressively take advantage of HTML5, but in the longer term it should absolutely become a mobile operating system of its own."

Facebook is lagging. Google+ is tied in very tightly with Android and Chrome already. Twitter is going to be built into Apple's iOS 5. Practice director Dan Shey is also quoted saying, “The interesting aspect in Apple’s and Twitter’s partnership is how it can provide iPhone users with a verifiable social identity for websites and apps. That gives developers a lot of scope to innovate in areas such as authentication, personalization and advertising. It’s a hint of things to come.”

Rural Broadband - Holland, Massachusetts

The Springfield (MA) Sunday Republican runs a Q&A piece every week titled Just Ask. this past Sunday a woman who lives in Holland, MA posted a pretty interesting question. Before we get to the question though, let's take a quick look at Holland (source Wikipedia). According to the United States Census Bureau: 

• The town has a total area of 13.1 square miles (33.9 km²), of which, 12.4 square miles (32.1 km²) of it is land and 0.7 square miles (1.8 km²) of it (5.34%) is water. 
• As of the census of 2000, there were 2,407 people, 898 households, and 668 families residing in the town. The population density was 194.2 people per square mile (75.0/km²). There were 1,317 housing units at an average density of 106.3 per square mile (41.0/km²). 
• The median income for a household in the town was $52,073, and the median income for a family was $57,024.
• Holland has it's own elementary school but is considering merging its elementary school with the town of Wales. Holland students attend Tantasqua Regional Junior High School (grades 7-8) and Tantasqua Regional High School in Sturbridge.

A typical rural New England town that can be compared to likely hundreds of other rural communities across the U.S. Now for the newspaper reader question.

Question: Is it true that Verizon Communications does not have fiberoptics in my home area, Holland, and that there are no plans to install same? What I have now is a dial-up modem with Verizon, and it is very slow. It takes 10 full minutes for me to access my checking account online, after four screen changes. I understand the need for security, but this is ridiculous. I’m a teacher and need to cover a lot of ground on the Internet in a single day. At such snail speeds, I’m limited to very few online tasks like collecting emails. Over the past three years I have made numerous calls to Verizon service to ask if I could sign-up for high-speed Internet service, and the answer was always “no.” 
In this year of speed-of-light communications, do I have any other options? 
– Kathleen McGrory, Holland 

And the answer from reporter Jim Kinney:

Answer: While it is true Verizon does not offer DSL service for people in your area of Holland, there are other options available. Cox Communications, Holland’s cable provider, does offer provide high-speed Internet in this area. Since you sent us this inquiry, we understand you signed up with Cox’s Broadband service and can now quickly access your checkbook online. Welcome to the 21st century, Kathleen. 
Verizon spokesman Philip G. Santoro said, “There just aren’t enough customers there (for Verizon) to justify the expense.” He suggested people like you contact their local cable operator.  He also pointed out that there is a third option, and that is Verizon Wireless’ 3G coverage, which would provide high-speed Internet through cell phone coverage.

Many small rural towns in the U.S. do not have any option except dial-up. It is upsetting to read the Verizon spokesman's honest answer regarding high speed landline based service in Holland. Nothing against Verizon - it's the frustrating reality of situations across our country. From a business perspective it does not make sense for a traditional telephone company to offer high-speed data service in a town like Holland. With current data caps in place from Verizon Wireless and other providers I don't see 3G (or upcoming 4G) services as a competitive alternative. 

Holland residents are fortunate they do have a cable option. Many similar communities in our country are stuck with dial-up as their only option.


9/14/11 at 7:28 PM

This comment came in from retired Cable Executive Steven Solomon via Google+.

Gordon, I would add this comment to your post. What is often invisible to the public is the real demographics of a community like Holland. I know about this first hand. I helped negotiate the cable TV franchise with the town on the part of the predecessor provider to Cox, Continental Cablevision.

As of 1994, of the 2,400 or so residents of the town, only about 600 homeowners lived in their homes all year round. The rest kept their residences as vacation or second homes. This put the full-time residents at a great disadvantage in getting broadband by landline of any sort.

Putting in broadband plant at about $20G a mile is not a reasonable business proposition for the private sector if the company is relying only on the margin earned from Internet (which now competes with phone and cable TV). Thus, I don't see any alternative to the private sector stepping in with the 21st century equivalent of rural electrification.

Memories of September 11, 2001

I first published this three years ago.

I was walking into the office when our technician told me a plane had hit one of the towers - he said "they think it was a small plane" and I did not think too much about it. 20 minutes or so later I was in a meeting and the same tech came in saying it was an airliner. We all left the meeting and turned on a small television in our lab. I also made sure I had a computer close by so I could watch email.......

At the time we were running a national listserv for a large group of community college faculty and administrators involved in a Working Connections grant with Microsoft and the American Association of Community Colleges (AACC). I've pulled out a few emails that came to the list. Here's one of the first from Mete at Borough of Manhattan Community College (BMCC):

11:50 AM, 9/11/01

It is chaos here, but everybody at BMCC is OK. We are closed for the day and the roads/subways to in/out of Manhattan are blocked. I am in Brooklyn (home) now and the sky is dark from smoke/ash/soot. I have a feeling it is going to take a long time to recover from this one.
Hope all is well with everyone around the country,

Mete

BMCC is on Chambers Street, next to ground zero and a college building was damaged from the attack. Mete was on the subway on his way in when the attack started and I believe he walked home to Brooklyn.

Here's a reply message from Lynn at the AACC in Washington, DC::

12:05AM, 9/11/01
We are ok here, but our office is closing so people can try to get home. The smoke from the Pentagon is visible from our 4th floor conference room. Most of the federal offices have now closed, a couple of subway stations near the Pentagon are closed, the streets are crowded with people driving and walking home from downtown offices, and cars with sirens go by every 5 minutes or so. Folks who live near Capitol Hill are sticking around the office until things calm down in that part of town.

Lynn

A flurry of emails went back and forth during the day from people all around the coutry. We were all worried, frustrated and upset about the attacks and our friends in New York, Washington and Pennsylvania. Here's a sample of the response from Paula at Richland College in Dallas:

11:50AM, 9/11/01
Thank you both for taking the time to provide us with an update of your safety. Our prayers are with you and all Americans during this tragedy. As in other states, thousands are donating blood. A major sports arena in Dallas has been setup as a blood donation facility. Churches are conducting special services. Please assist us to remain informed as to organizations/drives that are established that will provide direct support.

Paula

This came from Chris at the Fashion Institute of Technology (FIT) in New York City a few days later:

10:50AM, 9/14/01
FIT is safe and sound and open for business but few classes are running normally. It is hard to describe the experience of walking south on Manhattan's avenues and seeing a column of smoke where the World Trade Towers should be. When the wind shifts, the smell of the fire comes to Chelsea with a light dusting of the cement that is ankle deep a few blocks away.

We are glad to hear that all are well at BMCC and in Washington.

Chris

Here's a followup from Mete that was also sent on September 14:

12:36AM, 9/14/01

The building that we (CIS) dept was suppose to move this Sept., (but did not because of delays) is quite damaged. They are using our main building as command/triage/morgue center. We will be closed until the end of next week. The cleanup is going very slowly and there is very limited access to downtown Manhattan.

The subways are not running and all the outer borough are choked with traffic with people bringing their cars and parking them as close to Manhattan as possible. The air quality is bad, there is possibility that some more buildings (including our own that was next to a collapsed building) may come down aggravating the situation.

There are a number people that I know, with families, that perished in the bombings (we were going go to a 10th bday party this weekend, but the mother is missing - what do we do now ??) from my daughter's school and our neighborhood. But they are defiant, and most of the businesses try to operate as usual with a backdrop of surrealism...

Thanks for all of your e-mails and good wishes. We appreciate it and find comfort in them.

Mete

Hundreds of emails went back and forth over the next few weeks on the listserv. I've saved them all.

Greplin - Search All Your Data In One Place Immediately

I recently started using a new search utility called Greplin. Greplin, co-founded by 20 year old Israeli Daniel Gross, lets users enter credentials  to their Gmail, Facebook, Twitter, Tumblr, LinkedIn, etc accounts and then builds a custom search engine that will search through content in each allowed application. 

Most of us have got information coming at us from multiple sources (email, Facebook, Twitter, etc) and it's often difficult to remember where an important piece of information came from and is located. That's exactly what happened to Goss a few years ago - he was on his way to a party and was trying to find the address. He could not remember what app the invitation came in on and spent a while flipping through different apps on his smartphone before he found it. Instead of just complaining about it, Goss decided it was time to build a search engine that could be customized to search individual user content across apps.

Greplin has a “freemium” or free service along with an enhanced version that will search business apps like Salesforce for $5 per month or $50 per year. There are smartphone versions and a very nice plugin for the Chrome browser. Check it out.

Tropical storm Irene and The Connecticut River

This was my first week back from vacation and it was a busy one both inside and outside the office. Tropical Storm Irene came through last weekend and the flooding after really did some terrible damage and continues to impact people's lives from North Carolina to Maine..

Much of the rain that fell north of us from Irene eventually ended up flowing down the Connecticut River that separates Vermont and New Hampshire and splits Massachusetts and Connecticut. I drive by the Holyoke Dam every day going to and returning from work and took a few minutes to shoot some video on August 30, the day the river crested. I have never seen the river this high and this powerful. This was shot on the bridge connecting Holyoke and South Hadley Falls.



I could not believe the debris along with the color of the water.

Telephone Set Function 2. To provide the telephone company with the number the caller wishes to call - Part 2

In my last legacy Public Switched Telephone Network (PSTN) post I covered pulse or rotary dial service.  Let's look at dual tone multi frequency (DTMF) dialing service in this post.

The most commonly used method for inputting a number in the US and Europe is now the dual-tone-multifrequency (DTMF) signaling method. DTMF telephones are also commonly known as Touchtone telephones. These phones also use numerical keypads but offer an even faster way to signal the number to call by sending tones on the telephone line. The DTMF phone uses a 12-button keypad. When a button is pressed on the keypad an electric contact is closed and two oscillators generate two tones at specific frequencies. 

Telephone DTMF Keypad

These tones combine to form one sound to the listener, just like when two different musical notes on an instrument are played at exactly the same time. The combined tones are a signal for the button that was pressed on the keypad. The frequencies used are illustrated in the keypad diagram. For example, notice when the number 8 is pressed the frequencies 852 Hz and 1336 Hz are combined to form the number 8 tone. 

For the central office to accept tones from a caller, the tones must be at least 50 milliseconds long and also be separated by  a 50 millisecond pause. DTMF phones offer much more rapid dialing of numbers than rotary pulse methods with the average phone number taking 10 to 15 times less time to dial using a Touchtone phone. Not only are Touchtone phones faster, they are also more reliable because they do not depend on as many moving parts as a rotary phone.

In my next legacy PSTN post, I'll describe how a telephone is made to ring.