How to Hack a Headphone Jack

At some point in your DIY audio projects, you’re going to need a way to input audio into your circuits. One of the most versatile ways to do that is to use a 3.5 mm stereo audio jack. These can be salvaged from an old set of portable audio headphones. If you cut off the ear buds, you can plug the jack into an audio source and connect the wires directly to your circuits.

In this tutorial, I’ll show you how to wire the two most common types of audio jacks – 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 standard stereo headphones that don’t have a microphone. After you cut into the cable, you’ll probably find one of three common ways these can be wired:

1. Copper wire ground sheath wrapped around two insulated audio signal wires.
2. Two separate insulated wires, each with its own signal wire and a ground wire inside.
3. Separate insulated wires for the ground, right audio, and left audio inside a single cable.

Usually red wires are the right audio channel and blue wires are 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:

Depending on the type of plug, you may have access to the pins inside the connector’s housing. The wires are connected to the pins of the plug like this (image courtesy of Rob Robinette):

If you only need a mono input, the left and right audio channel wires can be connected together.

Once you’ve identified the wires, simply solder them to the correct input channels in your circuit, or attach pin connectors so they can be used in a breadboard.

TRRS Audio Jack

The TRRS audio plug is found on iPhone headphones and other headphones that have a microphone. After you cut open the plastic insulating sheath you’ll find 5 separate wires:

• Solid red wire: right audio channel signal
• Red and copper twisted wire: ground for the right audio channel
• Solid green wire: left audio channel signal
• Green and copper twisted wire: ground for the left audio channel
• Red and green sheath with a copper wire inside: Inner copper wire is the microphone signal, outer sheath is the microphone ground.

You’ll also find a plastic cord that’s used to strengthen the headphone cable:

The TRRS plug connects to the wires like this:

If you can get to the pins inside the plug’s housing, 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.

There’s a very thin coating of insulating material on each wire, which is how they can be bundled together without any plastic insulation. Before soldering or connecting them to anything conductive, run a flame over the wires quickly to burn off the insulation, then wipe clean.

Once you’ve done that, the wires can be soldered directly to the inputs on your PCB, or connected to jumper wire pins so they can be inserted into a breadboard.

There are two types of audio systems, stereo and mono. A stereo sound system has two independent audio channel signals, whereas a monophonic system reproduces multiple signals through one channel. 

AMPLFY speakers are designed as a stereo sound system. 

As such each speaker will be receiving an independent audio signal. The left speaker will be receiving a 'left' audio signal, whereas the right speaker will be receiving a 'right' audio signal.

The amplifier receives the audio signal from a source (Phone or an MP3 player) via either an aux cable (pictured in the gallery below), bluetooth or an alternative medium and sends the left and right signal to the corresponding speaker. If we were to dissect the Aux Cable, there would be three wires - a ground cable (usually black or a shielded wire), a right signal cable (usually red) and a left signal cable (usually white or yellow). 

In order for the amplifier to receive an audio signal, the audio signal cables from the LED control panel must be wired to the audio signal cables of the amplifier. However, because we are connecting the 'ground' of multiple signals, a 'buzzing' noise occurs. Therefore, a ground 'loop' isolator must be wired between the audio signal cables of the LED Control Panel and the Audio Signal Cables of the Amplifier. 

Update:

We have updated our LED Bluetooth Decoders to a newer version, which has the ground loop isolation function built into the chip. If your kit was purchased before Nov 2016 and has the ‘Ground Loop Isolator’ included in the kit, you will still need to follow this step. If you have the newer kit, instead of a ground loop isolator you will have a 3-pin cable, which will connect directly from the Amplifier to the LED Bluetooth Decoder. See the picture below.