Humans as elements of a circuit
Humans are amazing antennas!
Humans as antennas is an established paradigm and the works on Body Coupled Communications(BCC) and Personal Area Netwok (PAN) from the MIT media lab are at the frontiers of innovation based on this concept. Their works get into the technicalities of such a communication such as protocols, circuit design, etc. The only down side being that, the technology is inaccessible to the common man. If you still want to experiment with it, we have something that could get you started.
In this post, we connected the headphone jack’s mic wire to the human body and used it to transmit and receive signals through space – Wireless!
Why the headphone jack ? Why not? Not only is it something that is readily accessible, it also does not require additional hardware.
In this post, we demonstrate this idea by turning the drawdio circuit made by Jay Silver using the 555 timer ‘wireless’ by using the human as an antenna.
In order to make the drawdio circuit (see diagram below) wireless, take out R5 and place your hand instead to complete the circuit.
Hook up a headphone jack to your computer and listen to the signals received on your mic. Your body will act as an antenna and you will be able to receive the signal on your computer. Make sure to adjust the gain of the microphone accordingly.
(see our post – Preparing a headphone jack for hacking to know how to set up your headphone jack in order for this to work)
Now if you are aware about common grounds then the above video might not seem as appealing because the drawdio in the above case by powered by an Arduino connected to the computer which is receiving the audio signal. The same concept does work with different grounds as well as we demonstrate in the following video where the drawdio is powered externally through an OTG cable.
If you would like to transmit the drawdio output in the RF range instead, one can hook up the output of the drawdio to a crystal oscillator and touch the output wire of the crystal oscillator instead. In this video, a 32 MHz crystal oscillator is used and a FM radio app tuned at 96MHz is used to pick up the drawdio signal. This would be another way to demonstrate the idea of using the human body as an antenna.*
Instead of the drawdio, if you would like to transmit serial data from the USB port wireless, we can play the same game. Just place your hand on the TX pin of the USB-TTL and listen on the mic of the headphone.
What can you do with this ?
There are obvious limitations of using a headphone jack for BCC rather than something more dedicated as explored by the folks at the MIT media lab, this post is an exploration on how one can intuitively achieve this using the headphone jack.
*There is a great chance that many of you might have already tried this out in your car at some point.
** More explorations on the drawdio circuit click here
** More explorations on the headphone jack click here.