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Payphone Cellphone Handset

What do you do with a busted payphone?
That's the question I had to ask myself back in March of 2011. The phone, a Nortel Millennium operated by Telus, had been violently removed from its mountings and left on the sidewalk near the White Spot on Broadway. The coin box had already been taken, so making off with the quarters wasn't an option. But you can't really go out and get a payphone any time you want one (at least, not without risking arrest) so I settled on stuffing the dirty thing into my backpack and heading home, under the assumption that I'd find a use for such a cool item in no time. But it took quite awhile of staring at the mangled and rusty parts before a mod suggested itself. In the end I decided to try connecting the payphone's handset to my cell phone.

The first thing to do was remove the handset. These units are built to resist decades of abuse in outdoor locations, so everything is well overbuilt. But when the whole unit had been ripped off the back, there was nothing stopping me from removing components. The handset was fastened to the body by nothing more than a thick metal c-clip. Once pried off the entire swivel mechanism at the end of the handset's cable pulled right out of the body. And the wire within that braided cable terminated in a standard 4P4C connector, allowing it to be unplugged from the main board.

The standard plug gave me hope. I was initially afraid that the handset would be wired up in some bizarro fashion that would make it a royal pain to interface with anything. But if it had a standard handset plug on it, chances are it was wired the same way as a normal household phone's handset.

I decided to give it a test to see just how lucky I had been. I unsoldered the 4P4C socket from the payphone's mainboard and plugged the handset back into the jack. Then I cut one end off of a 1/8th stereo audio cable, touched the wires to the pins of the 4P4C jack, and plugged the other end into my PC's soundcard. Careful not to bump anything, I fired up a song. ELO's Telephone Line seemed a fitting choice. Moments later I heard the familiar '70s song crackling out of the handset. Success!

The payphone's little speaker was pretty low-fi, but it managed impressive volume. And when I repeated my test with the microphone pins I got far better quality than I would have expected for such a device. Again, the volume was more than enough. My impedance fears were fading fast.

The next step was delayed a few days. Even though the handset could be treated like a standard microphone and speaker, my cell phone (An HTC Dream with T-Mobile G1 branding) had connections for neither. The headset pins were all part of its peculiar dock connector. And while a few places online offered to sell me a compatible plug, I didn't want to wait for one to be shipped up. Instead I came up with a better solution. When the weekend rolled around I headed down to the Vancouver flea market and began digging through bins of cell phone headsets. In no time I came up with a little wired headset with the special HTC connector on it for $10. I would have paid just as much for the connector alone by the time it reached my door.

Once home I ripped the plastic housing off of the headset. Inside was a button to send a mute command and a volume slider. As soon as my soldering iron had heated I removed the stock mic and speaker. Moments later I had wires from the 4P4C jack soldered in their places. I plugged the whole mess into my phone and made a test call to Pentium. I could hear ringing in the handset! So loudly in fact that I had to turn the volume slider half way down. But while I clearly heard Pentium answer his phone, he wasn't able to hear me. Hmm...

A little reading suggested that the handset's microphone might not work if its polarity were reversed. I quickly swapped the wires around and tried again. Still I could not be heard. So I began looking at the wired headset's tiny circuit board to see if I could figure out what was going on. That's when I spotted a surface mount component no bigger than a grain of sand across the microphone pins. Whatever it was, I doubted it was doing me much good, so I unsoldered it. Suddenly the microphone came to life. The moment Pentium picked up my test call he could hear my voice. I had done it!

So overall it was a very simple mod with very fun results. I've enjoyed walking around the city talking into a payphone handset, and have received a number of entertaining looks. The sound quality is also a step up from my cell phone on its own. And as an added bonus, I can now set my phone in my room's window where the reception is good and still take calls on it.

Here's a shot of the finished product, with the remains of the headset wrapped in electrical tape.

Here is a recording I made with the handset's microphone.

And here is a video I filmed with Pentium's help to demonstrate the handset. Sorry it's a little rough, it was starting to rain and I didn't want any getting into my camera.

The next step will be to convert the handset to bluetooth!

Update: Here's an action shot from the 2011 Vancouver Mini Maker Faire. The big handset made it easy to hear calls over the racket of several thousand geeky people enjoying themselves.

Page created June 14th 2011
Last updated July 13th 2011

Oh oh, telephone line, give me some time, I'm living in twilight