Suppression of electromagnetic interference at VIn

Hello,

I am using an 8.5 V DC power supply from my home telephone system to supply an Arduino Uno board by VIn. Now, I get some noise on the telephone, probably by interference from the Arduino back into the phone system. Does anybody have an easy circuit to suppress those interferences to put between the phone system and the Arduino?

Thanks a lot!

Regards, Dondae

It is called a filter. I would at the very least put a large (10uF) and a small (1 to 10nF) caps on the input. Otherwise you need to figure out the frequency range of noise, and implement an appropriate filter. It sounds like you just need a low pass filter, but a standard RC one won't respond fast enough (and the appropriate sized R would probably limit the current too much). Wikipedia has some decent articles on this.

Use a different power supply... ?

That would mean an additional wall power supply (waste of energy). The power supply for the telephone system is connected to mains anyway.

Since I do not have an oscilloscope I will try the filter as suggested above. If this does not work, I will try different component values.

How do you know there is noise?

What kind of filtering are you using when connecting your arduino to the phone line?

When I pick up the phone there is noise in the line. I can hear it. I just connect to Arduino VIn and GND to the DC power supply of the home telephone system (it's an old analogue home system by the company "Quante" of Wuppertal, not available anymore)

Digital circuits, especially CMOS, put a lot of switching noise on the power and ground lines.

Install the 10uF and 0.1uF capacitors right at the Arduino end of the 8.5V line.

cjdelphi's solution is much more straightforward. Other than power, are there any other connections between the Arduino and your phone system? It is also possible that radiated energy is getting into the phone.

How about disconnecting the phone, when you are playing with your arduino ?

As well as the capacitors you need a seriese inductor. Add caps each side if the inductor. It should be as big a value as you can get hold of.

Grumpy_Mike:
As well as the capacitors you need a seriese inductor. Add caps each side if the inductor. It should be as big a value as you can get hold of.

This is what I was suggesting as well, but at the very least, add the small and large caps on the power input of the Arduino. That alone I imagine will drop down the noise by a lot.

I put this circuit between the Arduino and the phone system

470 uH, 12 R


8,5 V o------------------------||------------------------o Vin
| | | |
Phone | | | |
system 10 nF ___ 10 uF ___ 10 nF ___ 10 uF ___ Arduino Uno
| |
| | |
__|
| | | |
GND o------------------------------------------------------o GND

but to no avail. Then I noticed that my FritzBox WLAN Router is connected by ethernet to the Arduino with GND connection over the ethernet cable. So most probably I have something like a ground loop between the WLAN Router, Arduino and phone system. I now use the wall power supply of the WLAN router and have no more noise on the phone line.

Thank you again,

dondae

Good job tracking down the problem, and thank you for letting us know. This could help someone with a similar problem in the future.