Audio jacks have been around for decades and have been used in a wide variety of applications. while they are simple in their basic functionality, they can be used in complex systems. To better understand some of their capabilities, we’ll delve into the “guts” of these connectors and see what they have to offer. When looking at a data sheet for a seemingly simple audio jack, you’ll often find a variety of schematics with a variation of switches and connections. In this post, we’ll look at how to read these schematics, describe the various types of switches available, and discuss how they’re implemented in audio applications.
what is a switch?
In its basic definition related to electrical connectors, a switch is a device for making and breaking connection in an electrical circuit. audio connectors are available without switches, with simple switches or with complex switching systems. these switches are often represented on a schematic for the connector available in the data sheet. Below are some typical schematics showing some of those switch options.
Reading: Headphone connection diagram
How to Read an Audio Jack Schematic
Before we get to the switch function, we first need to understand how to read an audio jack schematic. audio plugs can come with as few as 2 conductors up to 6 or more conductors. For this example, we will focus on the standard 3-conductor stereo plug. Below is a plug diagram and basic schematic including typical terminal designations. this specific example does not include switches.
When reading the schematic, think of the plug being inserted from left to right to align with the respective terminals of the mating jack.
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Now, we are going to add a switch to the terminal 2 position (tip). The switch on the left shown below, is classified as normally closed because in the un-plugged state, terminal 10 is making direct contact (closed) with terminal 2. It would typically be referred to as a “tip switch” since the switch is located on the “tip” terminal. Now again, we visualize the mating plug being inserted from left to right. When the tip makes contact with terminal 2, it pushes this spring away from terminal 10 making the contact “open” between these terminals.
In a similar way, multiple switches could be present on different contacts. Below is an example of a 4 conductor plug, with 3 switches located on the tip, ring 1, and ring 2 terminals.
Even though this looks more complex, it is still has the same basic functionality of the single switch variation, except there are 2 additional switches present.
all of the switches we’ve seen so far have been normally closed switches. Some other switching functions would be classified as normally open, single pole double throw (spdt), and bipolar double throw (dpdt). many of these switches would be isolated from audio signals and could be used to control other parts of a circuit.
Are Audio Jack Switches Needed?
the application dictates how many and what type of switches are needed. If you’re just plugging your headphones into an mp3 player to listen to music, you don’t necessarily need an audio jack with switches. however, if you need to switch audio between speakers and headphones, detect when the plug is inserted, use the inserted plug to control other parts of your circuit, or are using an audio mixing console, you probably want to use a connector with a switching function. the following are some conceptual examples that could be applied to multiple applications.
switch audio between speakers and headphones
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In the first figure, the plug is not inserted, so the switches for terminals 10 and 11 are closed, routing the audio to the speaker. in the second figure, the plug is inserted that opens contacts 10 and 11, thus routing the audio to the headphones.
Detect When the Plug Is Inserted
Similarly, this configuration would activate a detection function when the contact of terminal 10 is opened by inserting the plug.
Controlling Other Portions of a Circuit Independent of the Audio Signals
In this example, terminals 4~6 are electrically independent from audio signals 1~3. this uses a spdt switch where pins 4 and 5 are connected in the unplugged state, and then pins 5 and 6 would be connected in a plugged in state. this could be used to switch between circuit functions “a” or “b” with the plug inserted.
By understanding how to use the various switch configurations within an audio jack and their function, you can utilize these interconnect devices in a wide array of applications to perform tasks of varying complexity.
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