Microcontroller switching affects other parts of circuit

[BenzT]

Hi,

I am switching the port D of the PIC microcontroller at 50KHz.

while(1)
{
LATD = 0xFF
DelayUs(10);
LATD = 0x00
DelayUs(10);
}

But the PORT D pins are not connected in circuit. They are free only.

But i am getting some high frequency, high amplitude noise in other part of the circuit ( analog amplifier ). If i commented the above program, there is no noise in the analog section.

I tried the above program for PORT E also, there too heavy switching noise presents on analog amplifier.

Why the microcontroller pin switching affects my other circuit?

 

[FvM]

Presumed your report is correct, no switching pin externally connected, there will be still power supply and ground switching spikes due to port pin capacitance. With insufficient power supply bypassing, the noise spreads allover the circuit.

 

[BenzT]

Well i have connected 0.1uF at the power pins of all the IC's. Also have connected 10uF electrolytic capacitor at the input and output of 7805 IC.

 

[andre_luis]

Well i have connected 0.1uF at the power pins of all the IC's.

You have to spread some ceramic capacitors along analog power supply section, not only close to IC's. Anyway, it is likelly having issue with grounding plane, perhaps not well sized or even analog and digital components not sepparated within distanced regions of the board.

 

[c_mitra]

But the PORT D pins are not connected in circuit. They are free only.

Very likely a layout problem; if the port D pin is not connected to any circuit part, please pull it up/down and your problem will magically disappear (hopefully!).

Pin left unconnected (unloaded) is not a good design habit but anyway check that the power supply is well bypassed.