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[on:]

My project consists of:

5 4051 multiplexer chips (31 pots connected to 4 chips, all connected to "master" 4051)
6 4021 registers (46 buttons)
4 74HC595 registers (27 LEDs)
1 LM324D amp

Now I was thinking of separating the power lines like this

+5V from arduino to 4021+74HC595+LM324D, GND from each of those chips to arduino GND
+9V to 4051, ground from those chips to GND of 9V adapter.

Why? Because I've learned 4051 are really sensitive. When there is nothing connected to Arduino except from those mux chips everything seems to work fine, but the more stuff I add readings become worse.

What should I do? I do not have much experience with grounds and larger schematics like this (larger for me at least) so please advise me.

[Reply #1 on:]

By "Arduino ground", are you using an actual Arduino board, or making your own PCB?  If you're doing your own PCB, don't run from IC to IC, use planes instead.

Biggest thing is to use 100nF caps on each power pin to ground.  Use a 10uF cap nearby each "group" of ICs to remove any power dips.  If you're making your own board, a 100uF cap at the PSU entry helps too.  If noise is still a problem, you may need to use inductors between noisy components.

[Reply #2 on:]

Make sure to connect all power supply grounds together. Your description does not read like you have.

[Reply #3 on:]

I would recommend de-coupling caps for every device.

[Reply #4 on:]

By "Arduino ground", are you using an actual Arduino board, or making your own PCB? 

This whole project is on one PCB. There are two ground planes - one for 4051 chips and one for the other ones. I attached the picture. Do note that the board isn't finished yet. The first GND plane (upper) will be connected to Arduino and other (lower) to 9V adapters ground. Is that correct anyways?

Biggest thing is to use 100nF caps on each power pin to ground.  Use a 10uF cap nearby each "group" of ICs to remove any power dips.  If you're making your own board, a 100uF cap at the PSU entry helps too.  If noise is still a problem, you may need to use inductors between noisy components.

So I should add caps to mux chips aswell?

[Reply #5 on:]

Both grounds will still have to be joined somewhere. Choose a single common point where the "bridge" should be.

Power bypass caps on EVERYTHING, positioned as close as possible to the chip's power pins.

[Reply #6 on:]

Can we clarify if ground for the 4051's means Vss or Vee?

[Reply #7 on:]

http://www.ti.com/lit/ds/symlink/cd74hc4051.pdf

Vee would be Gnd per TI's datasheet.

[Reply #8 on:]

http://www.ti.com/lit/ds/symlink/cd74hc4051.pdf

Vee would be Gnd per TI's datasheet.

They call Vss ground, not Vee.  We are talking about the CD4051, not the 74HC4051 though - there will
possibly be differences in thresholds.

I'm not sure you can reliably drive the control inputs from 5V when Vdd is 9V, it would be more common
for Vee = -5V, Vss=gnd=0V, Vdd=+5V from what I understand.

[Reply #9 on:]

Yes, unless you were running from a single supply. Then Vee = Gnd.

[Reply #10 on:]

It looks like the chips require split +/-5V supply.

you can buy +/-5V DC-DC converters, that's the easiest way to solve this.

[Reply #11 on:]

I'm having difficulties understanding this. So in short best thing to would be to just use Arduinos +5 power supply and use decoupling caps on every chip?

[Reply #12 on:]

You only need the -ve  where your "analog" signal is going negative.   As it would for a very
small AC or audio signal.

If your input signal is a DC analog signal with the same +ve and ground limits as your circuit,
you don't need the negative input and you can connect both Vss and Vee to ground.

[Reply #13 on:]

Maybe the simpler solution would be just to use caps on each chip, connect everything to Arduino except for potentiometers on another source?

[Reply #14 on:]

just to make sure that you don't get brown outs I would connect a LM7805 or buck ic to the 9V supply and connect all the 5V ic's to it. You cant overdo it with the decoupling caps.