Capacitors causing noisy potentiometer readings

Hi

I have an Arduino project where I'm using a max7219 IC to control a 2-digit 7-segment display. I followed the circuit tutorial HERE:

It works great, even though I don't fully understand what the capacitors are doing in this example as I'm fairly new to electronics.

The problem I'm having is that in the same project I have a potentiometer that's sharing the same 5V source, and the capacitors are causing noise and therefore resulting in fluctuating values.

How do I go about avoiding this since the arduino only has the one 5V source?

Those look like simple power supply bypass caps. Did I miss another one? How did you reach the conclusion that the capacitors are causing noise? It doesn't make sense.

Edit - hold on, I just read that all again. There isn't enough information here. We need to see a schematic so that we don't get bogged down in generalities.

We have no idea what the potentiometer does, or how it is connected. Or what the rest of the system looks like.

I removed the capacitors and the pot is smooth (but of course the 7-seg doesn’t work) so I know it’s the caps causing the noise.

I didn’t make a schematic, I just went straight to the board, but here’s a pic.

The pot is connected to the same 5V source and I’m reading it off A0 input.

Hi,
Ops pic.

Thanks....Tom... :slight_smile:

Hi,
If the way you can tell there is noise is because of the display, then how do you know when you remove the caps and have no display?

I removed the capacitors and the pot is smooth (but of course the 7-seg doesn't work) so I know it's the caps causing the noise.

Put a 100uF on the 5V supply on the protoboard, see if that makes a difference.
In your code you should have a brightness control, decrease that.

The fact that removing the caps results in no display is worrying.

The noise will be coming from your 9217 and the display multiplexing.

Please draw your circuit and post a picture of it.

Tom... :slight_smile:

TomGeorge:
If the way you can tell there is noise is because of the display, then how do you know when you remove the caps and have no display?

Good point...

TomGeorge:
Put a 100uF on the 5V supply on the protoboard, see if that makes a difference.
In your code you should have a brightness control, decrease that.

Remove the other caps? Or leave them all?

I will make a fritzing diagram shortly.

Hi,
Leave them all, keep the low value cap as close the the 9217 power input pins.

Tom… :slight_smile:

I will make a fritzing diagram shortly.

Instead, please make a pencil drawing on paper, and photograph/post that. It is easier and more likely to be correct.

Fritzing diagrams are usually misleading, difficult to interpret and often dead wrong.

flyagaricus:
I will make a fritzing diagram shortly.

NOOOOOOO!

Please, no pretty Fritzing pictures. They are NOT schematics. They are useless for engineering purposes.

Draw the schematic on the back of an envelope and take a photo of it- it will still be far superior to a Fritzing picture.

SteveMann:
Draw the schematic on the back of an envelope and take a photo of it- it will still be far superior to a Fritzing picture.

I really don't think you mean that. I wouldn't know where to begin.

One thing I noticed. I have a piezo buzzer that continuously buzzed until I connected the ground to it's own ground on the arduino and the buzzing stopped. So I connected the pot ground to the same separate ground that the piezo it connected to and it seems to have stopped the noise - but only after I added the 100uF cap as per Tom's suggestion. So, it seems bother are necessary, but I have no idea why...

I really don’t think you mean that. I wouldn’t know where to begin.

He really means that, we all do. Ok, maybe not an envelope but a piece of clean A4 paper. A hand drawn schematic, however scruffy it might be, is what we need. Drawing schematics is a required skill for electronics, time to start with your project. Honestly, do your best even if it’s your first attempt and not very good.

I agree, I need to learn, but for now - take a look at this fritz while I learn to draw schematics…

Hi,
OPs pic.

Put the wire going from the pot to gnd, closer to gnd at the other end of the board, next to the 5V wire going to the pot.

Tom.... :slight_smile:

Is this a rare example of a Fritzing diagram actually being more use than a schematic? :confused:

flyagaricus:
One thing I noticed. I have a piezo buzzer that continuously buzzed until I connected the ground to it’s own ground on the arduino and the buzzing stopped. So I connected the pot ground to the same separate ground that the piezo it connected to and it seems to have stopped the noise - but only after I added the 100uF cap as per Tom’s suggestion. So, it seems bother are necessary, but I have no idea why…

All the more reason for a real schematic. I have no clue what you just said. There is only one ground.

PerryBebbington:
Is this a rare example of a Fritzing diagram actually being more use than a schematic? :confused:

OK, you figure out his problem.

SteveMann:
OK, you figure out his problem.

Well Tom George did! At least I think he did. Would not have been clear on a schematic. I'm on a train heading for Paris at the moment, using this website on a phone is hard work.

take a look at this fritz while I learn to draw schematics

No thanks. Since the Fritzing Idiot Diagram has no pin numbers or labels, it is extremely difficult to verify connections.

Tutorial on schematic drawings here.

TomGeorge:
Hi,
OPs pic.

Put the wire going from the pot to gnd, closer to gnd at the other end of the board, next to the 5V wire going to the pot.

Tom.... :slight_smile:

Did that - the pot values are still jumpy. It definitely something to do with the display though, occasionally, the display just shuts off, and then the pot behaves normally, as well as the buzzer.

SteveMann:
All the more reason for a real schematic. I have no clue what you just said. There is only one ground.

What I meant is that I ran a jumper from one of the other Arduino GND pins to a separate area of the breadboard and that faithfully removes the (faint) buzzing of the piezo. If I connect the pot to this same "seperate" ground, it reads much smoother.