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Figure 4 - The RJ11 telephone jack will have a pair of wires leading to the main board
Figure 4 - The RJ11 telephone jack will have a pair of wires leading to the main board

The telephone will be converted into an audio mixer device capable of taking the output from your voice processing hardware (or computer) and inserting it into the phone line. The device will also let you listen to the audio from the phone line using a set of standard headphones. So basically, the phone will be converted to use a line input in place of the receiver's mouthpiece and a set of headphones in place of the receiver's earpiece. You will use the device to talk on the phone by speaking into the microphone plugged into your voice changer and listen to the call with a set of headphones. You will hear the person on the line as well as your own altered voice on the headphones so that you can hear yourself the same way they hear you. To make all of this audio mixing magic work as it should, this hack relies on the electronics included in the phone.

There are three sets of wires that you need to be concerned with: the telephone jack pair, the headset earpiece pair, and the headset mouthpiece pair. Starting with the telephone jack pair, you can find them by following the two wires leading from the RJ11 telephone socket as shown in Figure 4. There are only two wires needed in a residential phone system, and these correspond to the two center pins on the 4 pin RJ11 female jack at the back of the phone. Some phones don't have a jack, only the cord with a male connector at the end, but the wiring is the same, using only the two center wires. Usually, (but not always) these wires will be colored green and red for (tip and ring), so remember the polarity and position of the wires on the jack socket if you have to cut it to remove the circuit board from the phone. If you reverse the "tip" and "ring" wires, you may have a noisy hum on your phone when you use it again.



Figure 5 - This ugly mess is actually a fully functioning desktop telephone!
Figure 5 - This ugly mess is actually a fully functioning desktop telephone!

Once you have removed the circuit board entirely from the phone, solder any wires back where they belong and plug the mess into the phone hack to make sure it still functions properly. The receiver hook switch will probably be "up" already since the receiver no longer has a cradle, so the instant you plug the phone into the wall you should hear a dial tone. The ugly mess of circuit boards and soldered wiring shown in Figure 5 is actually fully functional, just as it was before I took everything apart. Now, we can begin reducing the phone to the minimal working size.

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