MSGEQ7 Breakout - first PCB

Hey guys!
I am designing my first PCB, a breakout board for the music visualizer IC MSGEQ7. I want to use normal resistors and capacitors (non smd) and solder the few components myself.

I started the PCB with Fritzing (might not be the best software for that but its okay) and i finished today.

What I want to know now is, if my PCB is okay. I am searching for a PCB tutorial which covers what is important when creating PCBs, not how to do it. I remember that someone said there should not be traces with 90degree edges or something like that. I never did that before, so is there any good guide you know? Or what should I change/improve/avoid/pay attention with my pcb?

The audio jack has some plastic pins at the bottom (marked black in Fritzing). Do i have to add holes there manually or will fritzing do that for me?

If I pay for a 55cm pcb and mine is only 33cm, will they cut off the rest? I just want a smaller one, thats okay.

Here some information about my current PCB:

Schematic:

PCB in Fritzing:

How it could look like later

Fritzing file is attached (schematic got a bit disordered after some changes).

MSGEQ7_PCB7.zip (21.6 KB)

Congratulations on trying to get a PCB made. It is really exciting the first time you get a manufactured board delivered and it looks like what you designed!

If I pay for a 55cm pcb and mine is only 33cm, will they cut off the rest?

You get the size of the PCB. The price break is UP TO 5x5, if yours is 3x3 then you will get a 3x3 in the mail.

The audio jack has some plastic pins at the bottom (marked black in Fritzing). Do i have to add holes there manually or will Fritzing do that for me?

That depends on whether Fritzing has the correct model for the device that you are using. In Eagle (what I use) if it is not in the model it will not get built that way. You can always cut off the plastic pins…

I remember that someone said there should not be traces with 90degree edges or something like that.

I am not an expert, but for something like you have here it will make little difference.

NOTE - I've never used the MSGEQ7 but I basically understand how it works... And, its a nifty chip!!!

It's a fairly simple circuit, but I suggest you build a breadboard version first, if you haven't already.

The MSGEQ7 is tricky to troubleshoot because you can't easily test it without fully-functioning software. And, some people have had trouble with the software. So, it's better to know that your software is working before connecting an new-untested PCB. If it works, no problem... But if the breadboard works and the PCB doesn't, you'll know where to look.

You'll still have to troubleshoot the breadboard & software together (if there's a problem) and you won't know if it's a hardware or software problem. But, it's better to get this out of the way before having a PCB made.

Okay thanks guys.
I will learn how to use eagle and copy my pcb there.

And yeah I know hot it works, I even made a homemade PCB and I developed the library on github :wink:

I will post my new eagle pcb sooner or later here again. Thx

So now ive redone it in eagle. May someone check the files? I used the sparkfun library to add some ICs.

Egale complains about the audio jack. Whats wrong here?

Also the vias have something eagle doesnt like.

I also made the PCB a bit larger so it also does not complain about the outline.

Should I round the pcb edges somehow?

Are the parts itself correct, standard parts? I want to use normal resistors, capacitors and pinheaders. The msgeq7 should be placed into another holder, to move it out again (like the Arduino Uno DIP Atmega chip). Do I have to change something for this holder?

I will try to place a ground plate and also add some text on the pcb for connections.

I also want to add a logo to the pcb. How do I do this best? Maybe I can move this to the copper field as a water trademark, not a white print. If you understand what I am trying to say. How to do that?

Anything else that could cause problems?

Eagle files attached.

MSGEQ7.zip (494 KB)

MSGEQ7_V4.zip (471 KB)

May someone want to check my new Eagle files?
Anything you would improve? Egale files attached.

MSGEQ7_V4 (2).zip (486 KB)

I'm using one of them in my last project and it works well :slight_smile:

test video

bought on ebay for some bucks

about your PCB be aware about the tracks clearance. like under R1 and under IC2
for the components use a MLCC capacitor for C3 and C7 (33pF) because standard through hole ceramic capacitors have a high...hum no, Very high temperature coefficient when they have low value (pico range) :wink:
(the one on the picture with black dot are not very good, they have very high drift compared to the low drift precision metal film blue resistors on its side xD)
so this cap is used as main oscillator as described in the datasheet. if the oscillator frequency shift the filter frequencies shift too :wink:

What do you mean by track clearance? What should I change, I dont really understand the problem.

Do you also know hot to connect the last 2 lines? Eagle DCR always complains about the hole. I can use audio jacks with only 3 pins, but if I could make both work this would be probably better. Also I have tried to edit that sparkfun package but had no success in removing the 2 inner pins. Could you help me with that?

Do you think I should connect the ground of the Audio with the Ground of the Arduino?

Generally one would say yes. But since I am having so many problem with unwanted audio noises i am a bit afraid of touching the Audio’s ground. Example: My Layptops PSU somehow generates to bad power, that the Audio has awful ‘knacks’ and high sounds in it. This also happens with USB soundcards. Meaning the problem is caused by a bad PSU and transmitted via the ground signal in all Laptop connected devices. So I am afraid that if I plug in my Arduino via USB cable, that the sound of will also disturb the MSGEQ7 attached sound device (pretending its another device playing the sound).

So do you think I should connect both grounds? Or should I place a jumper to manually change the connection? If yes, should it be closed or opened by default?

Any example capacitor I can buy?
The datasheet says they are ±2% is that much?
I also have this type:

And They also offer this (dont have this right now)

Edit: the maybe final? version of the board is now attached

MSGEQ7_V4 (4).zip (466 KB)

What do you mean by track clearance? What should I change, I dont really understand the problem.
the clearance is the space between two tracks, a track and a hole etc.
if you start a "DRC' you will have "clearance warning" because the space between two tracks is not enough.
here an example of the board I'm working today (4 layers) (I've modified the DRC rules to get example errors :wink: )

Do you also know hot to connect the last 2 lines? Eagle DCR always complains about the hole. I can use audio jacks with only 3 pins, but if I could make both work this would be probably better. Also I have tried to edit that sparkfun package but had no success in removing the 2 inner pins. Could you help me with that?[/b]
I can edit your board but it will not be totally your work at the end. You must do it yourself to understand the proscess :wink:

Do you think I should connect the ground of the Audio with the Ground of the Arduino?
yes the ground must be common. the MGSEQ7 create it's own mid reference voltage on the CG pin (pin 6 called GND in the datasheet)
here is my application schematic. you can see the ground is common

Generally one would say yes. But since I am having so many problem with unwanted audio noises i am a bit afraid of touching the Audio's ground. Example: My Layptops PSU somehow generates to bad power, that the Audio has awful 'knacks' and high sounds in it. This also happens with USB soundcards. Meaning the problem is caused by a bad PSU and transmitted via the ground signal in all Laptop connected devices. So I am afraid that if I plug in my Arduino via USB cable, that the sound of will also disturb the MSGEQ7 attached sound device (pretending its another device playing the sound).
I'm working on an audio product at my job (32bits microcontroller + sigma audio DSP chip) and I have the same troubles with noise from laptop.
it's caused by the little leakage current flowing through the isolation transformer (no earth connection on the laptop power supply) and from the Y class capacitor between the ground of the PSU output and the live circuit (but you must know the inside of the switching mode power supply to understand well :slight_smile: )

you can check this point by measuring the AC voltage between a real earth connection in the wall socket and the + or the - of the DC jack of the laptop. I'm pretty sure you will measure near 75V AC (110VAC here in France)
it's this current that create a little shock when you are touching two computers, with only one connected to the earth.

So do you think I should connect both grounds? Or should I place a jumper to manually change the connection? If yes, should it be closed or opened by default?
the ground of the arduino must be the same with the audio ground and the GND of the MSGEQ7.
if not you have the risk to kill the arduino or chip by the leakage current (high voltage peak discharge between the first side at 75VAC and the other side to the real earth level)
in the datasheet you can see VSSA ("A" for analog) it's the 0V for the analog signal

Any example capacitor I can buy?
The datasheet says they are +-2% is that much?
I also have this type:
http://www.reichelt.de/Scheiben/KERKO-500-33P/3/index.html?ACTION=3&GROUPID=3169&ARTICLE=9338&OFFSET=16&WKID=0&SID=11VM@Q3X8AAAIAABEfF648d3164518193942f1a8a8290c08c1fe4&LANGUAGE=EN
And They also offer this (dont have this right now)
http://www.reichelt.de/Styroflexkondensatoren/CY-22-2-33P/3/index.html?ACTION=3&GROUPID=3158&ARTICLE=42424&OFFSET=16&WKID=0&SID=11VM@Q3X8AAAIAABEfF648d3164518193942f1a8a8290c08c1fe4&LANGUAGE=EN

take the second one, it's much better
another one

Thx for this very good information!

I was talking about this last wire:

Now I edited the part and removed the inner 2 pins since I dont use them at all. I think there is no other way to wire them properly.

The ground problem:
I sure connect the gnd of the MSGEQ7 with the Arduino. I just wasnt sure about connecting this ground with the audio's ground.
So you would suggest to connect both grounds directly (in my schematic just remove the jumper), did I understand that correct? But then the Audio will output noises, you are aware of that?
If I do not connect them together, the ONLY connection to the Arduino is the 100nF capacitor of the Audio lines to the MSGEQ7. Only a capacitor, no real connection. Would this still causes any problems? I havent tested it though, because I dont have the hardware here right now. I was just afraid of the noises from Laptop.

Do you have any idea how to solve the laptop noise problem? A smaller PSU outputs less noise than the bigger one. (living in germany, 230V, laptop has 19V). I now try to connect the smaller one to the docing station and connect the sound to the laptop directly, so I have less noise and its quite acceptable. But I am still searching for a better solution. May another PSU help?

The guy from Reichelt support said that the first one only have +-2% while the 2nd has +-5% tolerance. Is is anything else important? What is different about the Glimmer capacitor? In your link you posted the one I also posted. Was this a mistake?

I was talking about this last wire:

Now I edited the part and removed the inner 2 pins since I dont use them at all. I think there is no other way to wire them properly.

the solution was to route the wire from the external side of the PCB :wink:

The ground problem:
I sure connect the gnd of the MSGEQ7 with the Arduino. I just wasnt sure about connecting this ground with the audio’s ground.
So you would suggest to connect both grounds directly (in my schematic just remove the jumper), did I understand that correct? But then the Audio will output noises, you are aware of that?
If I do not connect them together, the ONLY connection to the Arduino is the 100nF capacitor of the Audio lines to the MSGEQ7. Only a capacitor, no real connection. Would this still causes any problems? I havent tested it though, because I dont have the hardware here right now. I was just afraid of the noises from Laptop.

the audio signal ground must be connected to the board ground as a 0v reference. the ground will disappears with this reference.
The audio signals are AC so they are going through the 100nF cap . it’s a “AC coupling” capacitor to remove any DC bias voltage so no problem. (you can see C28 doing same job on my schematic)

Do you have any idea how to solve the laptop noise problem? A smaller PSU outputs less noise than the bigger one. (living in germany, 230V, laptop has 19V). I now try to connect the smaller one to the docing station and connect the sound to the laptop directly, so I have less noise and its quite acceptable. But I am still searching for a better solution. May another PSU help?

with the common ground the noise will be low if you are not using external appliance like audio amplifier or CD reader.
the ground is like the vintage LP player with the thumbscrew at the rear to connect the amplifier ground.

The guy from Reichelt support said that the first one only have ±2% while the 2nd has ±5% tolerance. Is is anything else important? What is different about the Glimmer capacitor? In your link you posted the one I also posted. Was this a mistake?

it’s a not a tolerance but a temperature coefficient problem.
cheap disc ceramic capacitor are a very high temp co. more when the value is low like 33pF
you can try to make an audio frequency oscillator with a NE555.
use a ceramic disc capacitor and listen the sound. if you heat the disc with your finger you can be sure the frequency will increase from low frequency to high pitch :slight_smile:
this is why on my schematic I’ve specified “C0G” dielectric. it’s a very tight tolerance and tempco dielectric.

So I will connect ground and change the pcb. thx!

Do you still think the traces are too close? The DRC check accepts them. (have a new version, below)

I am using external music boxes so it is a problem with the ground of laptop vs amplifier. May you explain a solution in a bit simpler way?

So the red capacitor from Reichelt is okay you think? I’ll probably order some then. Or ask a teacher :wink:

You noticed to pull some lines low in your picture before removing it. Does it matter for the Arduino breakout board? I dont understand what you mean by that note.

Another question: What if I check one audio check if its physically plugged in. If not it connects the audio lines to ground by default, so the audio signal is just silent. Would this work? Should I use a pulldown here or better not touch the signal at all?

PCB
Schematic

The PCB is very close to production. It can be found here:
https://github.com/NicoHood/MSGEQ7/tree/dev/board

I found another capacitor here. The datasheet says mlcc at one picture. So is this capacitor okay?

this capacitor is ok :slight_smile:
wich version of eagle do you use? because I can't open the sch or brd files.

Version 7.2 should work!? You could open the PDF or the png files to get at least an overview of the board.

I dont know on what values I should look. Maybe I can find a better seller, since Conrad is very expensive.

Edit: I think I want to order from conrad. I collected all materials, does this look fine to you (5 boards)? You can search via the "best-nr"

Is there any reason this PCB not be a 1/2" or so larger in both width and length? I appears that a little more real estate outside the component area could allow for more comfortable routing. - Scotty

Not really. I tried to make it as compact as possible (as always) and the routing seems fine to me. I only used 2 vias and made the Audio lines and VCC thinker. Any problem with this? As I said its my first PCB.

Hi Nico, did you ever produce these boards? Interested in buying some

Sparkfun has MSGEQ7 shields.
Leo..