Re: Signal interference in a long cable

On 12/21/2016 07:51 PM, Michał Pleban wrote:
> Hello!
>
> I am fighting with signal interference in a long cable. I have clock and
> data signals, plus some others too (they come from the C65 to the 1565
> drive).
>
> The signals interfere with each other, causing the clock signal to look
> like this:
>
> http://i68.tinypic.com/nqqth.jpg
>
> The longer the cable, the worse the signal distortion. The distorted
> clock signal confuses the shift register, making it shift some unwanted
> bits and causing corruption of the received data.
>
> I tried some simple stuff like termination but it didn't really change
> anything. Passing the clock signal via some receiver circuit (for
> example, 7414 Schmitt trigger gate, or a 75182 line receiver) helps
> *somewhat*, but with a long enough cable (over 1 meter) the distortions
> become too big to filter them out this way.
>
> I am not very goot at analog stuff, so I would appreciate any pointers
> to what can be done with this?

You have short spikes you want to get rid off. How about a capacitor 
between the signal and GND. Yes, that will soften the signal in general 
so you have to experiment if there is a cap that will work without 
softening the rising and falling edges too much. Put the cap at the 
input of the shift register or the 74LS14 if used.

Try 470pF and see what happens.

  Gerrit



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