Hi all

Thanks for the tips, maybe the 1-wire could be a choice.

But I was thinking about something like modulate a 15V line with the
i2c sinal, isn't it possible?

===========================  15V bus
    |                |
 ------           ------
|  15V |         |  15V |
| conv |         | conv |
 ------           ------
    |               |
    |               |
 --------        --------
|   i2c  |      |   i2c  |
|        | ...  |        |
| device |      | device |
 --------        --------

Do you think it is very dificult to design something like this?

Thanks a lot
Rodrigo


"Robert E. Griffith" <bob@JUNGA.COM> writes:

> The Dallas 1-Wire protocol does the same thing.  Many of their 1-Wire
> devices can use parasitic power meaning they need only a gnd and signal
> wires.  Normally they just suck up some power through the pull up resistor
> on the signal line while the signal line is not being pulled low by someone
> transmitting.  But some devices occasionally need more power than can be
> provided through the pull up resistor.  In that case the master can drive
> the signal line high through a mosfet for a period of time.
>
> In any case, maybe you can use the 1-Wire protocol.  Dallas has a 1-Wire
> master chip that can be controlled via RS232.  I am not sure how you can
> implement the slave end, but maybe Dallas has a chip for that also.
>
> --BobG
>
> -----Original Message-----
> From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On
> Behalf Of Bob Ammerman
> Sent: Thursday, March 06, 2003 10:44 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC]: I2C + Power supply through 2 wires
>
> > I need to connect a remote control (wired) to a main system, both
> > using PICs, through I2C bus. My idea is to connect using only 2 wires,
> > using those wires for power supply also. It would be something like this:
>
> I have done something like this using a proprietart synchronous protocol.
>
> In my case I only had to transmit in one direction, from the source of power
> to the target.
>
> I simply pulse with modulated the power supply. I used 3 different symbols.
> A zero was a 95% wide pulse. A one was 90% wide, and a special escape symbol
> 85% wide marked the start of a message.
>
> A diode and cap at the target held the power supply up during the low
> intervals of the pulses.
>
> You could implement a bidirection system by having the target drive a signal
> back on the power line during the low period from the source.
>
> Bob Ammerman
> RAm Systems
>
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