Noise problems

[Rob Northen]

I've made a little project with an Arduino, interfaced to a VFD.
It works great, except when I turn something on or off in my house, ex. a lamp. Then the txt on the VFD goes crazy, and I need to reset the board.

A few things I've tried;
-Running the board off diffrent power supply's (5v) both switchmode and one
with a transformer and DC-DC converter.
-Adding caps on the output of the powersupply, including plastic film and ceramic ones.

-Using and input filter in front of the powersupply (230v side), not sure what the filter is called, metal can with caps and inducters inside.


Nothing helps.

Any ideas ?

[Longbow]

Re: Noise problems

If possible, a schematic of your project would be interesting. The problem appears to be line voltage fluctuation, rather than rf interference. Possibly the chip is being reset when other appliances are switched on.

[Th3_uN1Qu3]

Re: Noise problems

If the power supply is regulated the problem is not line voltage fluctuation. It COULD however be a bad ground in the house wiring, which is a pretty serious issue.

If you run the project on batteries and it behaves, then you definitely have a grounding issue.

[Rob Northen]

Re: Noise problems

Its not a grounding problem or line voltage fluctuation, I'am a electrican myself and made the house wiring. When installed, ground was checked ok.
I'am getting more into its the cabel between the processor board and the display, its about 60cm long..

[Th3_uN1Qu3]

Re: Noise problems

Maybe you need more bypass caps then?

[joshnz]

Re: Noise problems

Its not a grounding problem or line voltage fluctuation, I'am a electrican myself and made the house wiring. When installed, ground was checked ok.
I'am getting more into its the cabel between the processor board and the display, its about 60cm long..

is the cable shielded? I guess not I have had some weird thing's happen with my projects all related to interference or cross-talk.

[Rob Northen]

Re: Noise problems

Problem solved, after putting pull-up resistors on unused digital pins on MCU...

[Longbow]

Re: Noise problems

Thanks for reporting back. Terminating all unused inputs on IC's, especially CMOS, is SOP because of their extremely high impedance. I came across a lot of equipment that had simple mechanical switches connected directly to a CMOS gate input. After a short while a tiny amount of oxidation on the switch, along with dust that settled on the switches would change the voltage on the input pins and cause unbelievable intermittent problems.

[ben7]

Re: Noise problems

Ah, yes, you should always use pullup resistors on any unused pins of ICs, or else there will be problems!

-Ben