Effect of mains interferance on low voltage power lines??

[ste2006]

Hi Guys,

This is probably an easy one but i am gettin myself a little concerned over a problem that may not exist,

I am being forced inside a chassis to join two boards with a 14 Way IDC Ribbon Cable, problem is the Ribbon cable needs to run close (maybe 25mm) away from an insulated 220V 50Hz mains supply, Both cables are only about 50cm in length but i am concerned about picking up interferance from the mains supply on to my ribbon cable.

At the far side i have two microcontrollers and some UART stuff going back and forward, Should the decoupling capacitors placed beside the IC already do the trick to get rid of any problems or should i add another low value Cap at the start of the board??

I think i am worrying about nothing but better to ask and be sure,

Thanks,

 

[D.A.(Tony)Stewart]

There are EMC standards for ingress that a designer needs to be aware of for interference. THese exist in Europe (CE) USA (FCC) and Japan as well as other nations.
We used to test for ingress with AC lines and brush type electric motors with data cables next to it for measuring coupling. So I would plan on designing a shield from ingress. THis can include; CM choke around cable, foil or braid ground plane, signal interface filters and TVS diodes.

I once designed a rocket remote control ground station with 2 computers in full duplex and a rack of multi-programmer HP equipment for battery chargers and ADC cards and MUX switches. The design was a success with remote control and CRT monitor of 96 functions (SCADA) in 1976, but the failure I learnt after I left for a better job, was the lack of attention I overlooked to the RS232 driver over the 1 mile distance from COntrol building to Launchpad.. THe Launch team's RF radio ingress cause data errors on the cable and total communication was lost during bursts. A CM choke and LC differential filter would have filtered the signals , had I thought of the customer supplied cable ingress problems.. Don't make the same mistake.

 

[ste2006]

even with such short lengths at 50cm you would think its necessary then yes??

Any need fo extra caps on the far power supply lines??

Thanks