Noise on Data Line. Need help

[Tiwana6330]

Its a really weird problem and I have run out of idea what to do. So I am hoping someone will help me here. Pl see the attached system diagram

**broken link removed**

So when the relay switches (switching voltage is 220v AC and Switched Voltage is 220V AC), it adds noise to data line (as marked in diagrams). There is no connection what so ever between relay and data line except the AC line.

The noise is just a few Nano-Second wide. As a start, I placed a RC Low pass filter on the data line but it didn't solve the problem (actually worse **broken link removed** ). The RC values are 330nf and 47KOhm resistor.

Any ideas what could be wrong or any possible fix? I can only add stuff to relay or the data line

 

[FvM]

There seems to be a problem with both attachments.

 

[Tiwana6330]

Do not know what went wrong with attachments. Here is the System Diagram



Here is the scoped signal

 

[siongboon]

It will be better if you can post the schematic or photo your setup propably.
The noise can come in from a number of means.

Do not know what went wrong with attachments. Here is the System Diagram

View attachment 67242

Here is the scoped signal
View attachment 67243

 

[FvM]

The waveforms show mainly one thing: Either the "LPF" itself is useless, the signal is completely bypassing it, or the measurement is not showing the signal correctly, e.g. due to unsuitable probing.

The filter values suggest, that the signal is very slow, so completely supressing the interferences with a filter should be easy. So if the waveform does show the real interfering signal or not, it's apparently bypassing the filter. If so, it's mainly a matter of circuit layout and ground wiring.