Do not connect a speaker directly to a headphone jack (Speaker Impedance)

During the early days of exploring the headphone jack, we did some crazy stuff all in the name of science. And although many of them resulted in ecstatic moments of awe that we cherished, sometimes things went a little out of hand. But we learned important things from this experience.

In one of our previous posts, we showed you how we nearly fried our headphone jack ( appropriately titled Don’t do this! ). And in this post we will show you how to keep your USB port safe while playing around with speakers.

Speaker Impedance


It is important to note that the speaker offers resistance to the flow of electrons. And when dealing with DC, we call it resistance but when one is dealing with AC it goes by the name of impedance.

And by virtue of Ohm’s law , we get that:

Lower the impedance → more current → greater load → increased power

Raise the impedance → less current → smaller load → decreased power

And as a general rule of thumb, small speakers (like the ones on your headphone) offer really high resistance to the flow of current and larger ones offer little to no resistance at all.

This caused us an Arduino because we accidentally connected ~4 Ohm speaker to the Arduino. And due to its low impedance, it became power greedy and destroyed it while also temporarily shutting down the USB port. So, yet another thing that one must be careful about.

How to be careful ?

Now that you know about speaker impedance and what it can do, we strongly suggest that you read the following article  to enlighten yourself:

Understanding Speaker Impedance





Preparing a headphone jack for hacking

This is one of the most frequently asked questions regarding our project on the headphone jack : I have an old headphone, how do I configure it to do all the stuff that you feature on your blog ? This post will be a pictorial DIY edition of it.

One of the first steps is to procure an old headphone ( in working condition or otherwise).


And then cut off the mic and the rest of the earphones with it. ( But don’t throw it away! ) The reason why we do this is because when you want to hack into a device, its a boon to have accessibility to the Input/Output ports.


When you strip open the wire that you have, in the case of a TRRS headphone jack you will find 4 wires (Left,Right,Mic and ground) and with a TRS (Left, Right and Ground). The next step is to attach female jumper wires to them so we can plug in anything we want.


These wires are not your conventional “plug and play” type i.e If you take these wires  and plug them into anything it won’t work. This is because they have a non-conductive plastic-like coating in them that prevents the wires from shorting.

Therefore soldering them to the jumper wire is a bit tricky. But in our experience it helps to preheat the wires before soldering and also to wrap the wire in a braid fashion for longer life.


And similarly you solder the rest of the wires as well. Now in order to find out which wire corresponds to what, connect a speaker between the Left/Right and the ground, plug it into your computer and start playing tones.


If you are asking where am I going to find a speaker ? Well just use the speaker from your headphone that you stripped off in step 1 and solder two wires to its terminals like the picture above and you are all set.



The headphone jack meets an actual spark gap!

So, we had the opportunity to test out the headphone jack with an actual spark gap and it was absolutely wonderful. Check it out:

With the data we can actualy find out the frequency of the spark occurrence. In our case it turned out to be ~ 34 – 36 Hz. And since this is in the Audible range we can actually hear this (somehow we missed this when making the video)

Screenshot from 2017-06-10 20:01:07

Audio file : GoogleDrive


Part – I – Lightning detector with a simple headphone jack

Part – II – Detecting switching ON/OFF of Tube Light using headphone jack

Part – III – Cigarette lighter spark detection using headphone jack


It is ridiculously easy to generate any audio signal using Python

Updated: May 15,2019

Now it comes as a surprise to many people when I tell them that generating an audio waveform is extremely simple.

One needs to have basic understanding on how audio signals work and basic python programming to generate any audio wave form. This post will show you exactly how.

Python packages needed: Numpy, Scipy


How to play the audio the generated audio file on computer ?

1. Command line using SoX

play -t raw -r 44.1k -e signed -b 8 -c 1 test.wav

where -r = sampling rate -b = sampling precision (bits) -c = number of channels

2. Use Audacity (check video)


Link to code : GitHub

You can find a list of other waveforms that can be generated using SciPy here

Known Issues:

[1] This does add any headers to the audio file and therefore you cannot play it on any media player as is . Check this reddit post if you really want to have one.

[2] Adding headers to the above code seems to be making it slower. And this is a problem if you want to make larger audio files.

[3] The code generates only 8-bit audio signal. Feel free to play around with the code to change it to other formats.

[4] A lot of technical details were conveniently not included in code in order to appeal to the theme of this post. And therefore this code is not “efficient”.

DIY: Obstacle detector with Audible feedback (IR sensor + Headphone jack + 555 timer)

We were inspired by the buzzer that you find in mobile and laptop showrooms – the ones that produce this annoying high frequency tone if you fiddle a ‘little too much’ with the displayed product.


We use a 555 timer in its Astable mode to produce the frequency tone and couple it with a digital IR sensor module. We do this by connecting the output pin and the ground parallel to R2 in the figure.


And as a result when there are no objects in the vicinity, the system produces a high frequency tone, but when an object is introduced the sound dies out.  This is attributed to the change in resistance value.

Here is another variation of the same:

Cigarette Lighter spark detection using headphone jack

This is part-III of the post series on detecting electromagnetic waves using headphone jack. In this we capture the EMW that emanate from the spark gap junction on a lighter. This is analogous to our gas lighter experiment but conducted at a smaller scale.

Screenshot from 2017-06-07 11:41:35

We say that this is analogous to the Gas lighter experiment because the waveforms obtained are extremely similar in nature.

Screenshot from 2017-06-07 13:35:47


Check out:

Part – I – Lightning detector using headphone jack 

Part – II  – Detecting switching ON/OFF tubelight with a headphone jack


Detect switching ON/OFF of Tube-light with a simple headphone jack

Now in our previous post, we established that the headphone jack can be used to successfully detect electromagnetic disturbances ( Sparks and Lightning ). In this post, we explore the interaction of the tube light with the headphone jack.


Here is a close up of the peak that you saw in the video:


Nowadays of course, we have moved on Non-flickering tubelights and it is highly unlikely that we might be able to detect the peculiar peaks that you see on this. But to be sure we are currently working on this and we will keep you guys posted on the results.

Also if we could incorporate this into a IoT network, things will go crazy!!!


*   Image Source

Lightning detector with a simple headphone jack

Okay, this probably one of those posts that is ecstatic to draft because of the shear wonder that it encapsulates. We captured lightning using nothing more than just a mere headphone jack and its so simple that anyone around the world with an access to an old headphone jack can do it too!



Take an old headphone jack and strip off the mic part and you are good to go OR if you have a dedicated USB sound card you can use that!



Sparks of any kind produce electromagnetic disturbances and it is these disturbances made by lightning that we will be detecting. That is the reason we are stripping off the microphone from the headphone jack and keeping only the wire.  The wire will act as an antenna to pick up the signal.

Just to be clear, this is NOT related to the sound of the thunder by any means.

Test with Gas Lighter

Before we test the headphone jack with lightning, we needed to know how the headphone jack reacted to sparks and how a spark looks like when recorded with a headphone jack.

Since gas lighters are capable of producing sparks, we thought that it would be a great place to start. Here’s what we observed:

** Although we use a USB sound card in our videos, this works with an ordinary TRS/TRRS headphone jack as well.

Capturing lightning

Now that we have a good idea of what is going on with a gas lighter, we can predict a similar pattern with a lightning as well. Why ? Well, because lightning is the same phenomenon but, at a much bigger scale.

How do you do it ? First things first, to state the obvious one needs lightning. But besides that the setup is similar to the previous one except that unlike the gas lighter, we have to use the human body as an antenna by holding the wire coming from the mic pin of the headphone jack in our hand

Processing the recording

The audio file that we acquired has been uploaded to Google Drive (links below) but we strongly suggest that you try it out yourself to get a feel for this powerful technology that many people disregard as quotidian.

This is how the raw audio file might look (recorded with Audacity):

Now we amplify this signal on Audacity. (Effect –> Amplify)



Now you see these three prominent peaks, now these are for sure caused by the lightning. How are we so sure? Well, we were able to visually validate the data. What are those other peaks ? They are lightning too (!!!), but ones that are happening at a distance (probably many kilometers away).

Now in order to be completely sure, we repeated the same experiment another evening.. And here’s what we got:

Screenshot from 2017-05-18 10:05:53

This was a much more dramatic day with lots of lightning! ( as is evident from the numerous peaks )

How cool is that you can something as simple as a headphone jack to procure information about lightning that is probably happens kilometers away. This was absolutely ecstatic!

What does one peak look like ?

Here is a close up of one peak that was recorded:


Sampling rate: 44100 Hz

Screenshot from 2017-05-24 12:43:23

Sampling rate: 384000 Hz

This resembles very closely to a Guassian Wave packet . ( In physics, a wave packet (or wave train) is a short “burst” or “envelope” of localized wave action that travels as a unit )


We believe that the electromagnetic disturbance that is detected during a lightning / spark is a Gaussian wave packet.  (If you believe otherwise let us know why by pinging us at or in the comments section)


Video Demo:

Will be uploaded soon! (subject to environmental weather conditions ;P)

If you found this post interesting, check out

Part- II-  Detect switching ON/OFF of Tube-light with a simple headphone jack

Part – III – Cigarette lighter spark detection using headphone jack

Part – IV –  The Headphone jack meets an actual spark gap!!!!!!

Thunder Audio file (44100 Hz): GoogleDrive link

Thunder Audio file (384000 Hz): GoogleDrive link

Don’t do this! – Headphone jack

Technically, one should not give more than 3V/3.3V (according to the Android Documentation) between the ground and the left/right/mic pin of the headphone jack. But there is this innate curiosity to know what would happen if one was crazy enough to do so.

We request you to not try this at home since doing this can damage your sound card! But nevertheless here is what would happen:

Testing basic headphone jack functions (Android)

In this post we will be trying to emulate basic functions as prescribed in the Android Documentation.  In order to understand the functions we first need to understand the circuit layout of the headphone jack which is as follows:

Screenshot from 2017-05-22 11:11:21

Now with this circuit in hand you can perform a series of tasks. This has been summarized in the table below.

Screenshot from 2017-05-22 11:03:00

This post will primarily focus on the Function A since that is the one that is commonplace in all mobile phones with a headphone jack. In the following video, we demonstrate how to emulate the following functions using a headphone jack

  • Play/Pause
  • Open Google Voice
  • Next song
  • Radio
  • Emulating Google voice