In case you haven’t noticed from my many comments on the subject, I drive a VW bus. It is a 1976 Westfalia camper with sage green paint and green plaid upholstery. I absolutely love it and so does the rest of my family. We go for drives in the country as well as camping regularly. We have found that the kids have a hard time communicating with us while we’re going higher speeds. These things aren’t the quietest automobiles in the world. Pushing this bread loaf shaped hunk of steel down the road with an engine that might top out at 75hp results in wind noise, engine noise, and of course, vibration.
I decided to employ a really old hack to put two functional telephones in the bus so my kids can talk to my wife (or whoever the passenger is) without screaming quite so loud. This hack is extremely easy, fairly cheap, and can be done in just a few minutes. The result is a functional intercom that you could use pretty much anywhere!
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.
While doing this project, I expected it to be mildly amusing. Possibly a unique use of the old hack. I was pleasantly surprised by my children’s reactions. I just installed this today and they’ve already played with it more than the Pinball Stomp that I built last time! This may have to become a permanent addition to my bus, if not, maybe it will be moved to their bedrooms.
For those who are interested in the mural on the ceiling, here you go.