Almost all cell phones and many DECT phones are equipped with a built-in speakerphone system. But wired devices often lack this function. A DIY technician familiar with electronics can add an external speakerphone to just about any corded phone.
Instructions
Step 1
Take any unnecessary cassette recorder. Open it, disconnect the shielded cable from the universal (non-erasing!) Head, lengthen it and lead it out. Cut at a convenient place any of the wires leading to the electric motor of the tape drive so that the connection can be quickly restored at any time in the future. Thoroughly insulate connections and wire cuts. Collect the tape recorder.
Step 2
Take a ferrite rod designed for the magnetic antenna of a medium-wave radio receiver. Wrap it with several layers of electrical tape, and then wind about two thousand turns of a thin wire in enamel insulation on top of it (for comparison, the coil of a magnetic antenna usually has about a hundred turns). Wrap a few more layers of electrical tape over the winding, first pulling out both ends of the wire.
Step 3
Connect the braiding of the shielded cable to one end of the wire and the center conductor to the other. Insulate the joints from each other, and then tape them to the coil with several more layers of electrical tape.
Step 4
Turn the recorder into playback mode. Pick up the handset on the corded telephone and try to find a point on its body where a beep is clearly audible from the recorder speaker when the sensor is located. If there is no such point, it means that the phone uses a transformerless conversational circuit, and you will have to look for the point of bringing the sensor on the receiver.
Step 5
Adjust the volume so that no acoustic feedback occurs. If necessary, place the tape recorder away from the handset microphone (this may require additional extension of the cable).
Step 6
If it becomes necessary to use the tape recorder again for its intended purpose, remake it back, because you left the universal head and motor in place.
