At some point in your DIY audio projects, you’ll need a way to input sound into your circuits. One of the most versatile ways to do this is to use the 3.5 mm stereo audio jack found on most portable audio headphones. If you have an old set of headphones laying around, you can cut the cord and wire the plug directly into your circuits. There are two common types of audio plugs. Each connector is wired differently, but I will show you how to wire each one so they can be used in breadboard or soldered circuits. The two most common varieties are TRS and TRRS. The T stands for “tip”; the R stands for “ring” and the S stands for “sleeve”:
TRS Audio Jack
TRS audio plugs are found on the standard stereo headphones that don’t have a microphone. There are several styles of wires used to connect TRS plugs to the headphone earbuds. One type has a copper wire ground sheath wrapped around two insulated audio signal wires. Another type has two separate insulated wires, each with its own left or right audio signal wire and a ground wire inside. The third type has insulated wires for the ground, right audio, and left audio inside a single cable. Usually red wires are for the right audio channel and blue wires are for the left audio channel. Check the image below to see which wires are audio signal wires and which are ground wires in the most common TRS wiring schemes (image courtesy of DIY Perks on YouTube).
The wires are connected to the TRS plug like this:
If you are wiring up a new plug, the wires are connected to the pins of the plug like this (image courtesy of Rob Robinette):
If you only want to use the TRS connection as a mono input, the left and right audio channel wires can be tied together into one. Once you have the wires stripped and isolated, simply solder them to the correct input channels in your circuit, or attach pin connectors to them so they can be used in a breadboard.
TRRS Audio Jack
The TRRS audio plug is found on headphones for the iPhone and other headphones that have a microphone. After you cut open the plastic insulating sheath you will find 5 separate wires. The solid red wire is the right audio channel, and the red and copper twisted wire is the ground for the right audio channel. The solid green wire is the left audio channel, and the green and copper twisted wire is the ground for the left audio channel. There is also a wire that has a red and green twisted sheath with a copper wire inside. The inner copper wire is the microphone line, and the outer sheath is the ground for the microphone. You will also find another plastic cord that is used to strengthen the headphone cable:
The TRRS plug is connected to the wires like this:
If you are wiring a new plug, the pins of the TRRS plug connect like this:
If you only need a mono audio input with the TRRS connector, you can combine the combine the red and green wires to make a single mono audio wire, then combine the ground wires to make a single ground wire.
Before soldering or attempting to connect the wires to anything, you should know that there is a very thin coating of electrically insulating material on each wire. This is how the wires can be bundled together without any plastic insulation. In order to solder them or attach anything conductive, just run a flame over them quickly to burn off the insulation, then wipe them clean.
Once you have done that, it’s a simple matter to solder them directly to the inputs on your PCB, or solder them to jumper wire pins so they can be inserted into a breadboard.