5 cent payphone coming soon.


Hi, my name is Allison, and I teach the Inkscape workshop at Metrix. Matt, the owner of Metrix, wanted me to write about some of the cool and interesting things I see at Metrix on a regular basis.

Over the past couple of days I’ve noticed Andy Filer, Metrix regular, working at a table covered in various phone parts. I asked him what he was doing, and he told me that he’s helping Metrix add a payphone into a small closet in a corner of the shop. He also told me that every call made from the phone would be five cents, no matter where in the world it was to!
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Obviously this isn’t going to be an average payphone. He’s been working very hard by taking out most of the non-mechanical insides of the phone and replacing them with a custom setup consisting of an Arduino, the insides from a different phone, an analog terminal adaptor, and a hand wired board that helps manage the accepting or rejecting of coins.

Since all of the insides of the phone were spread about and easy to see, I asked him to explain what exactly was going on when someone makes a call on this thing. What did he have to change to make it work the way he wanted? His answer was long, but I certainly learned a lot.

When you first put a coin into the phone, it gets sorted by the coin validator (common in payphones and vending machines). The validator has different switches that get flipped as different coins come in.  The Arduino watches the switches and makes a different beep depending on which type of coin (quarter, nickel or dime) gets put into the phone. These beeps then go through the terminal adaptor over the Internet to a FreeSWITCH server which makes sense of the beeps. (Before reaching FreeSWITCH the noises are treated like speech by other parts of the phone.) When you press buttons on the phone, they also make a certain sound that can get interpreted as numbers by FreeSWITCH. Metrix employee Duncan Smith, working with Andy, is working to program the FreeSWITCH server to understand the meanings of different sequences and lengths of frequencies. He will also have to tell it what to do once it receives those beeps.
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The Arduino doesn’t just know what the meanings of beeps are. Andy has programmed it to know whether the phone is on or off the hook, and also if the phone is being “supervised”. If a phone call is supervised, that means that it is charging for time on the line. If one were to call the operator or an emergency line for example, the phone call would not be supervised. Traditionally a call would only begin supervision upon someone picking up on the other end of the line. This information is sent by the phone network.

The Arduino also is connected to the innards taken from a separate phone. The interface between these two was also built by him. These phone parts oversee normal phone operations such as handling the voice through the transmitter and receiver in the handset.

Another interface written by him is from the Arduino to the board (wired by him) that controls the hopper relay. (The hopper is the part of the phone coins go to after being sorted.) This relay moves coins into either the coin box storage area or the coin return, depending on if FreeSWITCH decides to put the call through. There needs to be a separate board because the relay (a mechanical part kept from the original pay phone design) needs about 48 volts to operate. An Arduino only gives out about 5.

If the FreeSWITCH server knows that the amount of money that was put into the phone is correct, and it has a usable phone number it will put the call through. It does this through a VOIP service named, “Call with Us”.

So, did you get all that? (It certainly took me a couple of tries.) FreeSWITCH is connected to the terminal adaptor, which is connected to the Arduino. The Arduino is connected to the parts taken from another phone, the coin validator, and the accept/reject board. That board is connected to the hopper (which is fed from the validator), and it’s connected to both the coin box and coin return. A somewhat complicated system but very interesting to learn about.
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When asked why he wanted to work on this project, he replied, “There was a payphone around and it wasn’t functioning as is, so we wanted to see what made it tick. Then we knew it was possible to do something cool with it, so why not make it a real payphone? It’s funny. Have you seen a nickel payphone in the 21st century? It’s more of a 1940s thing.”

Definitely true. Currently the phone can make some calls, though Andy is still making tweaks to the inside. He hopes to have it installed by the end of the week.

It seems as though payphones are going to become extinct sometime soon. I wonder what would happen if all of the payphones in Seattle were retrofitted to make calls over Skype. Would people, perhaps those who normally couldn’t afford an international phone call, be more likely to use them? There has been a concern that VOIP services can’t make 911 calls, although Andy is addressing this issue by adding the functionality to the Metrix phone. I don’t see what could stop the city from doing that as well.

As we do move towards a system where more people own cell phones instead of landlines, I like seeing something like this phone act as a bridge between two worlds. So many people think that everything from the past has to be gotten rid of in order to move forward. Clearly that isn’t the case. I wonder about other kinds of old technologies that we’ve given up on that could maybe be given new life.

If you have an interest in creating new from old, come over to Metrix and experiment. Maybe you’ll even want to make a phone call or two.
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