Sending data to a smartphone via the headphone jack?

[fuzzybabybunny]

I've got this meat thermometer and the probe terminates into a 2.5mm male headphone plug. The resistance measured at the headphone plug corresponds to the temperature.

Now, I don't believe that smartphones can read resistance directly through their headphone jacks, right? The only way to have signal flow into the headphone jack is if the sensor was outputting different voltages, and then on Android or Apple use their "record microphone audio" API or whatever?

So if I have a sensor or a probe that I want to output into the headphone jack of a smartphone, I would need to have it powered and outputting voltage? Is there a simple way of doing this? I've got a Wemos D1 mini but an entire microcontroller seems like it would be overkill.

 

[Ken g6]

Thinking analog here...

This jack is both a microphone and a headphone jack, right? So I imagine that the headphone could output a tone, which could be sent through the resistor, and back to the microphone input. Then you could just measure the loudness of the returning tone. You'd have to study the system to figure out if you need an extra resistor in line for safe voltage levels.

 

[tynopik]

pretty sure you want a raspberry pi or something

 

[who?]

The "headphone" jack may be able to do whatever the circuitry tells it to since it's part of a smart device.

 

[who?]

Also "headphone" plugs are 3.5mm with two channels and a ground. The plug on the meat thermometer sensor may be matched to the electronic meat thermometer readout unit and not be compatible with a headphone jack.

 

[Kaido]

I've got this meat thermometer and the probe terminates into a 2.5mm male headphone plug. The resistance measured at the headphone plug corresponds to the temperature.

Now, I don't believe that smartphones can read resistance directly through their headphone jacks, right? The only way to have signal flow into the headphone jack is if the sensor was outputting different voltages, and then on Android or Apple use their "record microphone audio" API or whatever?

So if I have a sensor or a probe that I want to output into the headphone jack of a smartphone, I would need to have it powered and outputting voltage? Is there a simple way of doing this? I've got a Wemos D1 mini but an entire microcontroller seems like it would be overkill.

Yes, I have an anemometer (windspeed reader) that reads data through the headphone jack. Temperature measurement is doable as well; Thermodo sells a plug-in unit that does it:

https://thermodo.com

Might be worth plugging it in & seeing if any of the apps detect it, just for the haha's:

http://thermodo.com/software/

Although I'd imagine their temp readers are custom for the iPhone. Supermechanical has a meat probe more like what you're describing:

https://supermechanical.com/range/

Maybe download their app & try it out? See if it works, and if it does, compare it to a regular temperature-reader & see if it's accurate. Report back!

 

[who?]

The outputs to the headphone jack are probably selected by multiplexers that can be switched between audio and more practical circuits.

 

[Carson Dyle]

Like who? said, headphone jacks are 3.5mm. That 2.5mm plug is the size used by digital food thermometers. Which are cheap.