Need advice on filtering, customized Arduino board


Just finished a problem with the help of forum Gurus with signal level problem between my customized Arduino board and L293 driver board which I cnc machined and populated with components.

The problem solved by putting resistors between command pins of Arduino that go to L293 board and ground. After adding those resistors (of 100K).

Next I included my servo motor to the circuit. The new problem was unexpected jumps of servo motor. I thought this may be the same problem, and added another resistor, same 100k between servo pin on Arduino and GND. The problem solved and the movement went on more accurate than I have seen before on my servo and my original Arduino (well, this is qualitative so forget it:D).

Before, if I found such jumping on servo, I could thought that I need to include some more caps for filtering the noise, but now I need your advise to come to some deeper understanding, may be with some other tutorials about Arduino, signal level, noise filtering, if such tutorials now exist?

Could you please suggest the reason why such a thing happen, so I make a new Arduino DIY board that won't have this problem?

These are my boards:

one question came in my mind - do the servo's have their own power supply?

Do you mean battery source?

If so, the battery is one, but the servo has an LM7808, getting the power from there.

You mean I should have 2 batteries, separated?

Show us a schematic of the PCB alongside with a PCB layout with the component placement shown in the picture.

// Per.