Hacking a vintage phone into an old VW minibus to use as a kids/driver intercom

Caleb sez, "My kids really have to scream from the back of my VW bus for me to hear them while we're flying down the highway. With this little hack, we have a nice intercom for them to talk to me with!"

The circuit to make two phones work as an intercom is extremely simple. You can see in the picture below, all you really need is a little bit of spare phone cable (or a spare junction box), a resistor, and a power source. A single 680 ohm resistor should let you use the 12V directly from your car or even a standard 9V battery if you’re wanting to make this portable (in a treehouse for example).

This circuit allows both ends to be picked up and audio to be transmitted either way. If you want it to ring, you’re going to have to come up with a slightly different circuit. However, since you’re not using the black and yellow wires, you could theoretically rig up a circuit with a buzzer that would run off the normal 12V.

Using old phones as an intercom in your VW bus (or anywhere else) (Thanks, Caleb!)


    1. Like a home away from home.

      But the older they got the crankier they seemed… especially transmission wise 

      In 03 I got stuck on a steep uphill in Seattle by a stop light in thick traffic, too it out of gear by habit, realized I would need several feet of rollback to get it back into gear… sweat city.

    1. Clearly this is intended for use by a nondriving second adult in the front passenger seat, not the driver?  After all, without a ringing phone, the only way a front occupant would know someone in the rear wanted to initiate communication would be by turning around and looking in the back — not something to do when driving at 50 MPH.  And besides, if there wasn’t a second adult in the front passenger seat, why not have the kid sitting there?

      1. Well, I’m pretty sure someone right behind you can initiate communication without a ringing phone… aren’t you sure of that now too? :)

        But yeah it’s clearly for funsies not for while driving.

  1. I think it’s kind of sad that my kids will probably never experience a home land line or the joy of dialing your own number, hanging up, and then laughing as your parents answer and no one is there.

    1. Not a legal requirement, though I’d probably still retrofit them- my family own 2 old cars that were built without rear seatbelts (1965 Volvo PV544 and 1971 FIAT 500) both of which have had them fitted.

    2.  WTFV, you’ll see everyone wearing them while they try out the phone in the driveway.

  2. The VW minibus isn’t *that* old if it’s on a 12V system. Vintage VWs had 6V electrical systems.

    1. 45 years old is still pretty old.  Few families still drag their families around in 47-horsepower tin cans with optional seat belts.

  3. …Or, you could just put in some insulation. What I wanted for my bus was an auto-pilot so I could go back to grab a beer without pulling over.

      1.  I one made a cordless desk phone. I rewound the ringer coil with heavier wire to run from 3V and made a little square wave generator to send 20 Hz pulses to it.

      2. I hear there’s this thing called a “coil” which can supply between 10,000 and 30,000 volts to a spark plug, so it can’t be too tough.

  4. So where do you guys live that you assume it’s illegal for everyone to use a handheld phone if you’re driving? In the Great North, there’s no law against it (yet). I imagine there are plenty of other places where talking on a non-hands-free phone is still legal.

    1. Aw, there are those who would frown on driving kids around in a VW bus in the first place.  No airbags, no crumple zones, geared for a top speed of ~65mph, heater that burns gasoline… if I drove my kids to their preschool in one of these, somebody there would probably call the cops.  Who would probably respond to the call via their radio, with a handset.  Or are the fuzz all into the Bluetooth these days?

  5. You usually send 100 V AC through the same pair to get the phone to ring.  Ever been working on the line when someone calls in?
    The yellow/black pairs don’t carry the ring current.  They carry the signals for a second line.  You could add a fax machine to your van.

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