things to think about


today i’m thinking about: ELECTRONIC NERD 1
December 15, 2009, 2:51 am
Filed under: Uncategorized

So I was on this scrapyard trip last month. It was amazing. It is really worth its own business. But one of the things I found was this phone:

old phone

I dug it out of the side of a hill of garbage. This hill, I think:
IMG_0994.JPG

And as I was trying to decide what to do with it, I thought, of course I know what I want to do with it: I want it to tell secrets. I want you to be able to pick up the phone and hear a secret.

And off I went.

The basic idea is this: inside of the phone is an Arduino — a programmable microcontroller — running a WaveShield (which allows the Arduino to play sound off an SD card.) The hook switch in the phone would be an input to the Arduino, and when it is up (when the switch is closed) the Arduino would play a sound file through the speaker in the handset that plugs into the WaveShield’s 3.5mm output. EASY PEASE, RIGHT?

I mean, maybe to some of the l337 h@xxorz, it is. But this is my first major project with the Arduino, or with electricity and circuitry for that matter, and I am having to, to put it lightly, learn as I go.

Doing this meant breaking this down into many, many steps on a couple of tracks.
ARIEL’S TELEPHONE EDUCATION

Arduino Things
1) How do button presses work in Arduino?
2) How do I assemble the WaveShield and get *it* to work?
3) How do I get the WaveShield to play on a button press?
4) How do I get the button in question to be the hook switch (ie, how do I get the hook switch wired into the Arduino)
5) How do I get the hook switch to play a song?
Phone Wiring Things
1) How the fuck is a phone wired, anyways?
2) Can I pass current from a 9v battery through the hook switch to do things like light an LED?
3) Will the hook switch actually pass useful information to the Arduino?
4) How do I get the handset to connect to a 3.5mm jack?
5) Can I actually get the 3.5mm conversion to work?
Project Things
1) What sound do I want to use?
2) Just because I can get all the moving parts working, will the moving parts work together?
3) How does anyone ever do this without a computer science/electrical engineering background?!

As you can imagine, I have been learning a lot, starting with LadyAda’s Arduino tutorials, which got me through button presses pretty well (not perfectly.) I at least have some idea of how I might go about working a button to do something generally speaking.

From there, it was off building the WaveShield, which totally (miraculously) worked, including having to go buy a capacitor with the right level of capacitance, which meant learning wtf that meant and then going to the RadioShack and hoping that it would work even if the voltage (again, wtf does that mean?!) was higher (guess what? it does! hey thanks, capacitor substitution guide!)

Then, having exhausted my programming muscles on buttons and LEDs, I turned to the telephone, which is the bulk of this post. Did you know taking apart a telephone is actually really interesting?

Here are some pictures:
circuit board
coming apart
telephone in pieces

But here’s the real deal, friends: MAKING THE PHONE WORK AS A SWITCH. I did it, thanks to my SparkleLabs DIY electronics kit, this circuit diagram (caution, launches a .pdf) I found on the internet for the circuit board of the phone I am working with (dear the internet, thank you), and a lot of good old fashioned trial and error.

I do not feel like making a circuit diagram right now — I will for the final — so here is what happens:
5v power to the telephone positive line (the tip line)
positive connects through the hook switch to another line
that line to a 220v resistor to an LED to ground

and VOILA Y’ALL VOILA:

Why is it so exciting to have an LED that turns off when I hit the hook switch? Basically, it solves one of my huge problems: can I get the hook switch to work for me? I have some things to work with still, but this means the phone will talk to a circuit that I built. From here, the next big problem is getting the hook switch to talk to the Arduino, something I will do via the prototyping shield; concurrently, I have to start figuring out how to get the WaveShield to hook to a breadboard, 1, and 2, accept input from that breadboard. If I can do those two things, and I think I can, it is all gravy from here on out — just reapplying the same concepts.

Also, side project: following these instructions to get the handset to a 3.5mm. That looks easy, though.

So, in sum:
ARIEL’S TELEPHONE EDUCATION

Arduino Things
1) How do button presses work in Arduino?
2) How do I assemble the WaveShield and get *it* to work?

3) How do I get the WaveShield to play on a button press?
4) How do I get the button in question to be the hook switch (ie, how do I get the hook switch wired into the Arduino)
5) How do I get the hook switch to play a song?
Phone Wiring Things
1) How the fuck is a phone wired, anyways?
2) Can I pass current from a 9v battery through the hook switch to do things like light an LED?
3) Will the hook switch actually pass useful information to the Arduino?
4) How do I get the handset to connect to a 3.5mm jack?
5) Can I actually get the 3.5mm conversion to work?
Project Things
1) What sound do I want to use?
2) Just because I can get all the moving parts working, will the moving parts work together?
3) How does anyone ever do this without a computer science/electrical engineering background?!
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3 Comments so far
Leave a comment

Have you seen Citizen Engineer? http://www.citizenengineer.com/ Check out the video where she hacks a payphone.

Phone hacking is its own little subculture within electronics hacking. Personally, rather than learn all that stuff, I would probably just wire the speaker in the handset directly to the Arduino, assuming it’s the right kind of speaker.

Comment by Jon

that would be the easy way, but the trick is I want the sound to play only when the phone is off the hook, ie the switch has to be input to the Arduino. I tried wiring the switch into a breadboard and it didn’t run, but running through the circuit board to the breadboard seemed to work ok. Part of it is that I am still pretty new at electronics and this is actually not so bad with a circuit diagram so I can see how things run. Not ideal, but it’s okay. I tried taking the hook switch apart and it is the one part of the phone that seems to be pretty hard to get apart.

Comment by arielariel

This is many, MANY kinds of amazing.

Comment by Meredith




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