Re: Signal interference in a long cable

Depending on what you are up to you might want a completely different design...balenced lines and twisted pairs, do a Google search and some circuits should pop up


* Micha?? Pleban (lists@michau.name) wrote:
> Hello!
> 
> Francesco Messineo wrote:
> 
> > what kind of termination did you use?
> 
> I tried a termination resistor. I used a potentiometer to try different
> values from x Ohm to xxx Ohm, none had any visible impact.
> 
> > What gate drives the signal?
> 
> I believe it's a HMOS-II chip.
> 
> > Is the power to the driver and receiver chip very well bypassed?
> 
> I am not sure what that means :-(
> 
> > if it's really an "interference" (the exact term here is crosstalk)
> > between two signals, you have to run a GND wire between each two data
> > (or clock or whatever else) wires. That's how original parallel SCSI
> > and HPIB bus cables were made. Of course these busses are also *very*
> > well terminated.
> 
> That is a good idea, but it would mean I had to make my own cable
> instead of using an off-the-shelf one. I can go there, but as a last resort.
> 
> > It might be a termination issue or a bypassing issue likely.
> > You should first try to add a 47 ohm resistor just before the cable
> > beginning at the driver side, on every signal (but VCC if any and
> > GND).
> 
> Another good idea, but soldering resistors inside a C65 gives me chills
> for some reason ;-) The receiver is also meant to work on a sock machine
> without madifications.
> 
> > The take a picture of the scope with AC coupling, gnd clip on gnd pin
> > of the driver and probe tip on the VCC pin of the driver. The do the
> > same on receiver chip. This will show you if there's any ground or
> > power bounce (bad decoupling in this case).
> 
> I will do that tomorrow, thanks.
> 
> > Also, whenever you suspect a crosstalk issue, take a picture of both
> > signals, not just one :)
> 
> There are six signals in the cable, plus GND and reset. I am not sure
> what crosstalks with what :-(
> 
> Regards,
> Michau.
> 
> 
> 
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