Or maybee: How to ground?

I am designed a AT89C51RB2 "powered" officemachine controller. I am in doubt, how to connect my digital ground to the chasisground. This device is a class 1 thing - its made of iron, and connected to mains, and not doubleisolated, so it should have its chassis connected to the mains earth (with a yellow/green wire) for safety reasons. As we know "mains earth" is NOT something nice, great omnipotential nothingnes. Its more like a electric/electronic garbage can, carrying al sorts of noise at almost any voltage levet betwen zero and aprox 50V AC - at least in europe.

For screening reasons, I would prefer to connect my digital ground to the chassis, but I dont want all the trash from the mains earth. I the analog world, one would do it through something like 50 ohm in series with some 10 nF to get the screening effect and break the ground loop. But I am not so shure about "good engeneering practice" when it comes to the digital domain.

Any comments apreaciated.

Ha' en god dag

Per Guldmann

So should I just connect my digital ground to this