Actually I'd like to eliminate any noise from
public main ac power line, because if there
any appliences no matter how small if connected or
disconnected to power line contributes
some noise. In this case my application might be
too sensitive.

Hallo Kurnia,

if you fabricate +5V for your micrcontroller system with the help of classical design, means using mains transformer + rectifier + electrolytic storage capacitor + voltage regulator, this should normally be enough to suppress switching noise on mains voltage to an acceptable level. You can check this by the help of an oscilloscope connected to the output of 5V regulator, while introducing noise on mains e.g. by unplugging heavy loads like 'rice cookers' (nice example, makes me hungry!).

But may be there's something wrong with your power supply unit? Besides others, possible reasons for misfunctioning are:

1. Too small power rating or secondary voltage of mains transformer.
2. Too small capacitance of electrolytic storage capacitor. Sometimes, this can be observed, when the capacitor is an old or poor one. Then, try a new one.
3. Neglected necessary decoupling capacitors arround voltage regulator. Two 100nF X7R ceramics from input pin to 0V pin and from output pin to 0V pin is a good remedy.

In any case, you can test any eventual malfunctioning by the help of an oscilloscope: Is the output voltage remaining constant, without showing any glitches or dips?


I think it's more probable, that noise is entering your system via IR circuitry. If here high gains are used in combination with poor ground routing and/or neglecting of any shield (Faraday cage), then noise from mains voltage can very easily enter your system via stray capacitance or inductive coupling.

If this is the case, only improving your IR circuitry can help. Can you give some details about your IR circuitry? A schematic would help really much!!! As registered member you can easily publish a gif-file here...


Kai