Making your own Smartphone Cable
Many users, while enjoying the SpikerBox demo’s we have done, have also expressed excited curiosity that the iPhone/Android can be used as a portable data recorder/oscilloscope. To truly take advantage of your iPhone/Android though, you want your signal to go directly into your phone's line input. Though you can buy a cable to do this, in the open-source spirit of Backyard Brains, here is the schematic to build your own. You need: one 4.7 kOhm resistor, one 10 uF capacitor, one 3.5 mm audio three conductor cable you cut in half, and one 3.5 mm audio four conductor cable you cut in half. Bring out your soldering iron, your wire-stripper, and your favorite beverage!
Wrap all exposed wire in electrical tape, cover with heat shrink tubing, and you’re ready to rock! This design splices the left and right audio channels in the microphone input, so if you use this cable to record music, you are only recording in mono.
This of course is our favorite use…
Also same thing (functionally) can be done with just ONE piece of cable as the resistor & the capacitor can easily fit inside of the 4 pole jack plug cover (so the ground/earth continues through the whole length of the cable giving us less chance to catch unwanted noise and since there is no joint in the middle of the cable it is also more durable).
Just screw the outer shell of the plug and the cable is ready to "rock and spike".