Serial over Skin?(Capacitance sensor/transmitter?)

I remember reading somewhere about a chip that let you transmit data over skin. I have no idea if it was every more then a concept. I was thinking about maybe transferring a byte of data between two people when they touch (and are also touching their arduinos or the sensor of course). It could make for an interesting project.

Anyone know of such a sensor/transmitter?

Thanks -Francis

PS Its been a few years since I've been involved with microcontrollers and I'm back and loving every moment with this thing. Everything you guys have done (from the board/chip to the libraries you've produced) has made my experience quite wonderful. I'm very happy to be back into EE again.

Interesting, not seen that before but I assume you could do it easily using some sort of FSK (frequency shift keying), like the old modems used to do. Only using a higher frequency to get a better signal, maybe up at 100KHz or so.

I don't know if you've seen the Drawdio but they've got a video of people touching each other to complete a circuit. Might be worth a look:


I could probably use the drawdio's signal to detect presence but I'd like to communicate some data. I did some more research last night and it looks like there are two companies 3 years ago that announced chips that were like rfid's but instead of proximity it was touch oriented. I unfortunately can't prove that they ever released any products. One was NTT's RedTacton and the other was ...I can't find it now. If I could get a part number I'd hit up mouser but I can't even find their companies listed.

The FSK seems like the right idea, it seems to be used primarily for radio (FM being a form of it) but that's ok, a weak enough signal and you have to touch the receiver for it to pick up a transmission. =) I have no idea what kind of voltage i'd need or how the properties of skin affect it or even any chips to support encoding decoding, but I'm starting my research. (I've got about 8 different wikipedia and google tabs open)

I was wondering if I could just use pulse width modulation instead as that (producing and reading pwm) is built in to the audrino. According to the docs analogWrite() producing a pwm with a freq of about 490 Hz, a far cry from 100khz. Maybe there's an easy way to encode/decode that pwm on a 100khz carrier? Or am I getting ahead of myself and ignoring an easy uart/serial, shift register or parallel (hopefully ttl) chip that does the FSK?

the atmega168, which is the chip that some of the arduinos are based on, are more than capable of 100kHz pwm. you should be able to do that in the arduino environment. but it may not be as straight forward!

I don't see why PWM wouldn't work as well as FSK, it's just with FSK you can get a better modulation index and it is a bit easier to decode than PWM. You could also use CW, that is bursts of tone, long and short a bit like Morse code.