iPhone Remote Control

Simple iPhone media control button with backlight using audio jack.

I know what you're thinking, how can the iPhone audio jack power a backlight? Because the iPhone (& other smartphones) use a 4 pole audio jack ordinarily used for 2-way audio devices.

So the iPhone can power a red LED (other LED's require too much voltage) across the mic/control pin & common ground.

This also explains why a load resistor is required for an external remote control button to work.

The 100n capacitor is used to stabilize the button input & backlight power.