AVR Freaks

A block diagram would help; perhaps (also) a schematic ...

@DocJC. The technique is valid of course, but creating a 100mV offset or so seems more logical.

I left it deliberately to OP to figure this out (he already mentioned 2 resistors in his first post) to keep it "short".

My posts tend to get rather long sometimes...

Jo forgot to put a junction/ dot on the crossing between the resistors & the speaker output.

Why all those dots on the speaker? All insignificant.

A bit more sophisticated:

Without adding any external resistors you can put a varying DC bias on the "Audio input".

Then you can measure the RC time constant on the speaker output with the ADC.

I thought you wanted some kind of feedback to a uC ?

Using relays and mosfets seems like overkill for a circuit like this.

Another technique is to put a resistor in series with the audio and simply short the "output side" of the resistor to GND with a transistor or Fet when you want the output to be off.

But for really good advice we need to see the whole picture. Where is your audio coming from? Is there a uC nearby?

If so, then why do you need detection?

If it has anything to do with the "waterproof" ness of your connectors. If the inside of the connectors gets wet while there is a DC voltage present they will corrode. You will need a different kind of circuit for that.

My first vote is with AwNeil. Go get yourself a waterproof plug with the switch built in.

If that is not an option, then measuring the RC constant seems second best.

If waterproofness is an issue, beware of DC voltages and electrolysis.

(No intention to insult), sometimes I just can't resist letting some typo's be for wahat they are.

Of course audio is an AC signal. If audio were a DC signal your ears will get filled with audio and burst.

It's also why C1 and C2 are in the last schematic. They block the DC part.

Part of my advise was based on the assumption you could make your audio source emit a DC signal for headphone detection.

The circuit as you have drawn it is exactly what I mean.

Unfortunately I've made an error there, I did not think it through completely.

If you put a 1k resistor in series with an 4 Ohm speaker you wil not be able to get any decent sound level output.

Shorting the  signal to GND is only a viable option with high impedance inputs, such as an opamp buffer in the place of your speaker / headphone.

After all these posts I get the general idea that your experience level with electronics is not very high.

I want to reccomend that you build some ciruits on a breadboard. Find out your self what works, and what does not work.

In the mean time you'll boost your general knowledge of electronics.

That said, one can use the internal pullup of the AVR.  IME (at least in one app) the weak internal pullup is defeated [enough] by the low impedance connected device that it nicely reads logic 0.  Pin change can be used to detect some plugging/unplugging changes.

But then the AC coupled drive to the speaker/headphone would swing the I/O pin below ground, and the protection diode would take the brunt of it.  Wouldn't you need a high-value resistor before the I/O pin?

In my world: Draw dots to connect wires.

No dot == no connection.

There is nothing wrong with 4-way connections.

No dot is no connection, just 2 wires.

A dot means a 4 way connection.

It's not my rule I just follow the rules of my PCB Package (KiCad)

But I believe there is pretty much a consensus on this.

And for everybody else reading this:

Please stop using the "arcs / bows" to let a wire jump over another wire. This was amost abolished in the '70ies and '80ies when schematic entry programs became common.

I have never ever seen a  schematics package that uses them. Maybe some insignificant niche program uses it.

And it didn't even work properly on paper. Tried to draw such a "bow", made it a bit too small and it looked like a "dot".

Only DaveCad still uses it.

It's simple:

Wires do not connect untill you connect them. Wether you do it with a green dot or with a dab of solder does not matter much.

All those arcs and bows in a cable conduit of cables trying to avoid touching each other is a big squimy mess.

Something resembling this:

https://www.autodesk.com/products/eagle/blog/top-10-tips-draw-next-schematic-design-like-pro/

First, whenever you have two wires that form a junction and share an electrical connection, that intersection needs to have a junction dot. This is standard practice in every schematic design, and some tools like Autodesk EAGLE will add the junction dot for you

When adding junctions for intersecting wires, it’s also recommended to avoid a 4-way intersection as this will likely add to the confusion when reading your circuit. Instead, opt for a set of shared intersections as shown in the image below where each junction has its own unique connection. This makes it much easier to understand exactly the proper connections and avoid misinterpretation.

https://webcache.googleusercontent.com/search?q=cache:n3a1z2Hcbt4J:https://www.revolvy.com/main/index.php%3Fs%3DCircuit%2520diagram%26item_type%3Dtopic+&cd=9&hl=en&ct=clnk&gl=us

Wire Crossover Symbols for Circuit Diagrams. The CAD symbol for insulated crossing wires is the same as the older, non-CAD symbol for non-insulated crossing wires. To avoid confusion, the wire "jump" (semi-circle) symbol for insulated wires in non-CAD schematics is recommended (as opposed to using the CAD-style symbol for no connection), so as to avoid confusion with the original, older style symbol, which means the exact opposite. The newer, recommended style for 4-way wire connections in both CAD and non-CAD schematics is to stagger the joining wires into T-junctions.^[3]

The linkages between leads were once simple crossings of lines. With the arrival of computerized drafting, the connection of two intersecting wires was shown by a crossing of wires with a "dot" or "blob" to indicate a connection. At the same time, the crossover was simplified to be the same crossing, but without a "dot". However, there was a danger of confusing the wires that were connected and not connected in this manner, if the dot was drawn too small or accidentally omitted (e.g. the "dot" could disappear after several passes through a copy machine).^[4] As such, the modern practice for representing a 4-way wire connection is to draw a straight wire and then to draw the other wires staggered along it with "dots" as connections (see diagram), so as to form two separate T-junctions that brook no confusion and are clearly not a crossover.^{[5] [6]}

For crossing wires that are insulated from one another, a small semi-circle symbol is commonly used to show one wire "jumping over" the other wire^{[3] [7] [8]} (similar to how jumper wires are used).

A common, hybrid style of drawing combines the T-junction crossovers with "dot" connections and the wire "jump" semi-circle symbols for insulated crossings. In this manner, a "dot" that is too small to see or that has accidentally disappeared can still be clearly differentiated from a "jump".