Hacking Analog Phones For VOIP


[Tyler] has been using Google Voice extensively for some time now, but he hasn’t quite found a microphone/speaker setup he is happy with. He tried a headset, but that just didn’t do it for him.

While browsing around at his local thrift store, he came across an old Model 500 rotary phone for just a few dollars and decided it just might do the trick. Once disassembled, he mapped out the circuitry and got busy wiring up the handset to a pair of 3.5 mm stereo plugs – one each for the earpiece and microphone.

Once everything was reassembled, he hooked it up to his computer and gave it a spin – success!

While he is happy with how the phone works at the moment, he already has plans for improving it. He is currently looking for a way to use the handset hook to disconnect calls as well as a way to implement the rotary dial for number entry. We think that hacking a Bluetooth headset would easily take care of the first part, as well as eliminate the need for any sort of wired interface to his PC. It would also make it dead simple to use with any other Bluetooth-enabled device such as a cell phone.

We’re pretty sure he is open to implementation suggestions, so let us know what you think.

30 thoughts on “Hacking Analog Phones For VOIP

  1. I, too, have a 500 set hooked up to make voip calls through google voice. A SIP or IAX ATA that supports pulse dial, and a relatively recent version on asterisks makes it work just about like it did when it was connected to a line provided by the phone company. I picked up an Innomedia MTA6328-2Re on ebay for ~$12 and never looked back.

  2. I don’t want to sound mean but since when wiring a mic and a speacker to a sound card is a hack? If it was done by my 10 years old nephiew it would…

    If it were more like weregeek sais i wouldn’t complain.

    Is it me or lately hackaday is featuring all kind of mundane things?

    PS: Sorry for my english

  3. -The most elegant solution would be a composite USB device. I think that’s too much work.
    -Audio is essentially taken care of.
    -Getting the hangup and dialing to work without Asterisk would likely require a custom application running in the background, a custom driver, or both.
    -Or you could make the numbers a numeric keypad, and leave hangup alone, but this wouldn’t be a seamless solution.

  4. A nice hack. While the hand set on these older phones are much easier to use than contemporary phones/hands sets, one would still have to hold it against your shoulder to still use the keyboard. Things like that, and men sitting on fat wallets all day fills out chiropractor’s daily schedule. While it certainly would be more expensive than a 3.99 thrift store purchase. and junk box parts, I’d suggest making a true communications headset for multitasking. Like what radio operators or call center operators use. Me if such a phone still worked I plug it into my POTS. Somewhere around here I still should have a functional trim line pulse dial phone if not two. Ma Bell didn’t demand them back after the break up, and neither billed me for them. That or the old SWB charge me so little, I don’t recall the cost.

  5. So all you did was splice two wires together? You should check out the link in the above comments to see how to really mod the phone. In that mod they actually add components and functionality to the phone. How do you plan on interfacing with the Google voice app if you only added a headphone cable to the hand set?

  6. A model 500 handset is the ultimate in ergonomics, till your shoulder comes into play.
    I would like to cram my dumb cellphone into one. There are people that put cell units into old classic phones.

  7. Sparkfun had the right idea, but the Bluetooth phone they sell doesn’t work well and even they admit it.
    Of course, they don’t tell you that until after you purchase it, but its pretty much defective by design and they know it.

    If someone could actually make a Bluetooth one that worked, it would be a happy day indeed!

  8. Generally, I wouldn’t call wiring a speaker and mic to existing hardware a hack.

    Then again, if you can get the rotary pulses to translate into dtmf or serial signals, this will be a masterpiece.

    I remember reading an article about a guy using an old school non-digital modem (complete with acoustic coupling device since Ma Bell had some strict rules back then) to interface with the internet on modern hardware.

    If anyone can get an old school teletype machine on the internet with minimal usage of modern hardware… now that’s a hacker. :P

  9. Hey everyone! Thanks for the comments and such, I’m glad you guys liked it.

    Yes, this is not much of a hack. It’s really just step one in a process of many steps which I am still in the planning stages of. I bought the phone, and did this within 2 hours. I’ve only had it for 24 hours now, and I’m simply expanding my knowledge base about these phones before I do anything further, primarily because I want to do as little damage as possible to the original guts of the phone.

    yes, you could buy one of the modern ones or set it up through an ATA, but really this was about the challenge of the thing itself, not just the solution.

    My future plans involve a. better cabling system, making use of the actual RJ jack on the back, b. and arduino to translate the pulse dial into actual signal that can be used as essentially ‘quick dials,’ and somehow getting the bells set up. Then, yes, it’ll be a solid hack. :D This is just my first step.

  10. If he’s going to consider decoding numbers to run stuff, he should make a visual radial menu on screen (usually used with number pads, and sometimes in games).

    Technically it’s a hack because it requires them to use a device in a non-standard way and to modify it. Granted it’s a fairly simple one

    It looks like some of the early modems were literally dumber than dirt, all they did was modulate the signal sent to them and received, without doing handling, error correction, or anything else at all (the user even had to manually call and hangup).By that measure. they are actually REAL modems, not smart devices.

    The internet case is significantly helped by the fact that that guy was more or less dialing to access a system and running a web browser remotely. That’s not too hard because of the prevalence of dial-up internet and modem standardization early on.

    What would be a real hack, and likely impossible would be to enable calling or answering multiple phones simultaneously with the same modem by fudging some of the signals to a phone and the computer.

  11. I’ve got a Western Electric 1D2 pay phone. I have a future project to create a device that precisely emulate central office functions. But in the meantime I think I’ve come up with a hack.

    There’s a chip on the 32A frame that generates the beep tones but I suspect it does more. I’ve got to do some circuit tracing but I think I can get the coin values off it. I can mount an LCD above and use it as a piggy bank in the interim.

  12. I got a hold of a Western Electric 5302 for cheap recently. I bought a rotatone (http://www.oldphoneworks.com/rotatone-pulse-to-tone-converter.html) to convert it to modern day lines. It hooks up to my Vonage line, and it is fantastic. I like these old phones a lot more than modern plastic excuses.

    The rotatone is installable without any permanent modifications. My phone looks exactly the same as it was when it was new. It also comes with a polarity guard so you can’t damage anything.

    *I don’t work for that company, I’m just a satisfied customer. It’s well worth the price.

  13. @Dave – “I remember reading an article about a guy using an old school non-digital modem (complete with acoustic coupling device” : What is a non-digital modem? How does it interface with a computer if there’s no digital part?

  14. if he were to use an avr with the usb keyboard and mouse library then he could use the same avr to read the tones and the cradle for the phone. essentially it would be like a usb number pad.

  15. Just stick a small cheap VoIP ATA in it and replace the cord with an Ethernet cable. Heck if you don’t want to hack the phone at all, just plug it into an external ATA box, you don’t even need the computer any more!

  16. Wow, lot’s of anger too…

    Uh, just to repeat. This is just step one of the hack for me.

    Yes, there are better solutions out there, but I’m not paying $100+ for a bluetooth phone. I wanted to make this myself, without spending money.

    Same for the VoIP atas, I’m not interested in spending money on that sort of thing.

    To some of the others: I’m not sure what you mean “pretend telephony.”
    I’m not inserting pretend telephony into anything. I’m modifying the telephony that already exists to work with a totally different purpose in mind.

    Sure, the push button phones are easier to hack so the buttons work, but thats because they operate on an entirely different principle, and are much easier to adapt to modern use. Pulse dial phones are much more antiquated, and the translation is much more difficult.

  17. Well you should really work on the mod for more than two hours before posting it to a site like this. It seems like most people commenting have done more with a similar hack that you have done yet.

  18. this is a nice idea Tyler. Great job on the writeup.

    let me brainstorm with you .. the POTS basically used a two-wire system for the whole phone, for pulse generation and for the audio bits.

    now, obviously you only want to use the shell of the phone, so how about this ..

    the cable from PC to phone will be a usb cable that goes to a simple hub inside the phone. connect a usb headphone to the hub and merge it with the handset.

    modify the rotary dial, put an arduino or something inbetween the dial and the usb hub, and push out keypresses for the numbers you dial.

    you’ll probably need a listener program in the computer, that wait for input from a particular usb device, and inputs it into your google voice program. but you get the idea.

    great work, and I am eager to see how you progress.

  19. A “non-digital” modem is just like it sounds…an analog modem actually anything that isn’t an analog modem(modulator/demodulator) isn’t a modem it’s an adapter. The interface could be as simple as plugging in to the mic and line in jacks but that was harder to interface with the software so it was done with the serial interface…but it is still analog communications. I followed the link for the rotatone and that device looks cool but the “pre-made” phones are insanely priced.

  20. “Well you should really work on the mod for more than two hours before posting it to a site like this.”

    I could be wrong, but I’m pretty sure he didn’t post it to HAD. HAD did.

  21. What’s with the commentary on here?

    This mug will have a masterpiece on his hands when he’s done. I wish him luck.

    Sorry for causing a whole “non-digital” deal. In my mind (a land far, far, away) a device with no transistors is not digital.

    If the modem has nothing but an RC oscillator in it. I wouldn’t call it digital.

    Heh, lets start arguing about how digital Morris Code is now. ;)

  22. I think this is a great first step to an awesome hack. Been using google voice myself exclusively for months now (not for any great experiment, but because I am broke and my neighbor doesn’t secure his wi-fi- free phone can’t be beat). I hacked an older phone for a voip solution several years ago, and although it’s not a huge accomplishment, it’s definitely reminded me that I still have that phone somewhere, and could use it now.sometimes this simple stuff is interesting, and is a step toward a more complex hack. I like it.

  23. Use a Grandstream HT502 ATA and a Netgear WNCE2001 WLAN-to-RJ45 Adapter. Your vintage phone with rotary dial will function properly with any SIP provider. The only wire needed is to power the two aforementioned high tech devices.

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