Two Arduino boards sharing data through a living biological body - Page 1
Forum section: electronics / general

author: gioblu
author_rank: Newbie
timestamp: May 10, 2017, 01:40:38 am
content: Hi there, I am new, nice to meet you all!Compliments to the creator for the instructive and interesting videos! I really have appreciated free energy debunking, really funnySo, I am dedicating my time to an opensource communication protocol, or better network protocol stack, called PJON:https://github.com/gioblu/PJONI have developed personally one of the available physical layers, called PJDL:https://github.com/gioblu/PJON/blob/master/strategies/SoftwareBitBang/specification/PJDL-specification-v1.1.mdThe quite interesting thing I have noticed is that it is possible to get a reliable communication channel (with acknowledge, so bidirectional) using my body touching with the left hand the IO of an Arduino and with the right the IO of another (that are both sharing ground), here is a video of an experiment showing that through my old oscilloscope:Is this something standard, achievable also with other single channel physical layers and standards?Is it right to consider this experiment as a proof tha PJDL has high resilience to high resistance/capacitance/interference communication medium?

author: Rerouter
author_rank: Super Contributor
timestamp: May 10, 2017, 02:28:39 am
content: its somewhat expected to work, so long as your input data is immune to the massive amount of mains hum the human body acts like an antenna for (at my workbench i put out 22V AC into 1 megaohm)your skin resistance is somewhere between 1500 ohm and 400K ohm depending on the day at DC, at AC it gets much harder, as meat is naturally capacitive. , the input resistance of an arduino's gates are generally well above 100K ohms, so at low speeds, it would just come down to your contact resistance as to whether it worked reliably or not,at higher speeds, its harder,

author: Ian.M
author_rank: Super Contributor
timestamp: May 10, 2017, 03:13:07 am
content: seehttp://www.microchip.com/design-centers/embedded-security/reference-designs/bodycom

author: gioblu
author_rank: Newbie
timestamp: May 10, 2017, 01:54:44 pm
content: Thank you for your feedback, I have tried today with 1-Wire and it doesnt work through my body

author: hfleming
author_rank: Regular Contributor
timestamp: May 10, 2017, 04:58:46 pm
content: Biological tissue is ver diificult to characterize. Not only is it dependent on the cleanliness of the skin, but also on the amount of sweat in the contact are, but also on the salinity of the sweat that depends on our body. In addition, between a battery also form between the electrodes and skin, and after a couple of seconds (or minutes) iontophoresis will start taking place due to the skin-electrode batter effect, thereby changing things. As soon as you go to AC excitation of the skin, things become even more complicated, as now you have different electrical characteristics for each layer of the skin, not even talking about fat. Add to that, your body also generates its own electrical signals (muscle contractions), and that your body acts as a huge antenna picking up any external electrical field, like mains.Sure, if you use very low datarates, you might get a signal through from your finger to your toe, but that is about it.

author: tablatronix
author_rank: Regular Contributor
timestamp: May 10, 2017, 06:27:05 pm
content: Didn't MIT media lab or someone do this a while back, I think their POC was exchanging "business cards" with a handshake.

author: gioblu
author_rank: Newbie
timestamp: May 10, 2017, 07:50:37 pm
content: QuoteCiao hfleming, I detect 70-90% reliability with bidirectional packet delivery (with ack) at 39.800kBd or 4.975kB/s and it works passing through the whole body connecting two arduinos touching one with the left hand, the other with the right one.I do consider 40kBd as not so slow rate, but maybe we come from different fields and our perception is different

author: bktemp
author_rank: Super Contributor
timestamp: May 15, 2017, 07:58:13 pm
content: It isn't suprising that using flesh as a conductor for a low data rate is working. It is just a (not very good) electrical conductor, but some resistance doesn't care for data signals since there is no current involved, als long as the capacitcance is low enough to not distort the signals too much.If your protocol is good enough, try it again without any external GND connection (for example connecting one board to one hand and the other board to the other hand without any other wires going from one board to the other board).It is possible to transfer several MBits/s through the body like this pill camera does: