|iPhone as a frequency generator|
To show that iPhone is not just a fashion accessory, as many like to say, read below how to make it a useful device. It is a frequency generator with solid characteristics. Quality will satisfy the needs of amateur electronics and it will be sufficient for the basic measurements and adjustments in audio technology.
Is a frequency or test tone generator application over the range of 20Hz - 20 kHz, and it is possible to choose between waveform: sine, square, triangle and saw. Thanks to quality of audio output for headphones, which is built into iPhone, frequency accuracy is very high. The output is near CD quality (44,100 samples per second, 16 bits/sample)
iPhone has a 3.5mm connector on top to connect a headset and microphone, and we are going to use it for our cable. On the picture below, see the pinout of iPhone plug. All you need to do is connect the test probes between the (Ground) and left or right output for headphones, I decided to use right (R Audio Out). It is important to note that you should use shielded cable to block external interference.
The first thing you need to get is a 3.5mm plug, the iPhone uses version with 4 pins, but also receives regular with 3 pins that you can find on regular stereo headphones. My adapter is made from old stereo headphones. We need only one cable, so the other can be removed like shown on picture below. Plug is factory connected with shielded cable so no soldering is needed on plug, unless you use new 3.5mm plug. In this case, solder shielded cable to selected pins.
Another thing to get is laboratory test probes. Plain alligator clips can be used. I recommend test probes like on image below, they are easy to solder and very practical for use.
Remove the insulation from the shielded cable. Unroll shield from center wire and gather it into one braid.
On copper parts apply thin layer of solder for easier soldering. On shield solder another wire that will lead to black ground probe.
Over joints mount heat shrinks (Reychem) for isolation. You can use ordinary lighter if you do not have a torch or hot air soldering iron for heat shrinks.
Solder wires to test probes. Central wire goes to red probe and shield to black one.
That’s all, I recommend checking of all connections and wires with multimeter to ensure that everything is connected properly.
A short video of everything in use