single wire signal transmit

[sstimuluss]

back once more to tap the collective wisdom..
could someone please tell me whether the circuit below would work? or it just wishful thinking?

a 555 output connected via resistor to n-mosfet, to oscillate an LED powered by a separate battery..

this particular circuit is just for research purposes, i'm trying to find a way to transmit a pulse via skin contact between two otherwise isolated circuits, so the 1M resistor represents light skin contact

 

[Russlk]

There has to be a return path for the signal. The capacitance between the sender and receiver could be the path; how is it configured?

 

[AllVol]

What if the skin resistance provided the return path? In other words, touching a proper contact might provide the return.

 

[Sceadwian]

http://www.amasci.com/tesla/tmistk.html

It's easier just to run a second wire though. If you have one, what's wrong with two?

 

[ljcox]

And you have not included any electrostatic protection for the gate of the MOSFET.

 

[sstimuluss]

There has to be a return path for the signal. The capacitance between the sender and receiver could be the path; how is it configured?

I will use a configuration similar to what RonH suggested for transmitter and receiver:

Frequency division multiplexing:
Each circuit has an oscillator (relatively low frequency) connected to one electrode, and a tuned amplifier connected to the other electrode, and a synchronous demodulator following that receiver, the output signal being proportional to the resistance between the electrodes. You would then use that output to drive your MIDI transducer. The frequency selectivity would cause it to reject signals from another electrode, which would be at another frequency.

What if the skin resistance provided the return path? In other words, touching a proper contact might provide the return.

http://www.amasci.com/tesla/tmistk.html
It's easier just to run a second wire though. If you have one, what's wrong with two?

hey you're both absolutely right! (and thanks for that very interesting link!)
slightly modified the circuit above, and using an 4071 OR gate and NPN transistor instead of mosfet.. palm sized contact surface area per electrode

it works when all four contacts are touched, although the LED signal is a little weak and i can just just feel the current spiking along to the pulse (AC?)

when the two electrodes connected to ground are directly connected to each other (ie. common ground), the LED pulse amplitude is at maximum.. So in the skin resistance network, Hi output from 555 is being biased lower by a resistive contact to 555's ground, , voltage at OR gate is also biased lower via resistive contact to LED's ground, and this weakens the amplitude of the pulses.

through the skin, 555's ground is resistively connected to LED's ground though which is the important part.

i wonder if it needs so much current, perhaps i just need stronger amplification on the receiver end so that i can weaken the transmit signal..

 

[sstimuluss]

And you have not included any electrostatic protection for the gate of the MOSFET.

true, the circuit's pretty rough.. thank for pointing that out