UNO R3, MP3 shield, amp y148

[batarale]

Hello,

Although i don’t know anything about electronics i decided to build my first arduino project.
Only because i can see this absolutely great community that is involved and actively share knowledge
So thank you in advance for your help and have patience with this noob

Idea is simple. Play sound in house when someone open the door in back yard.

What i did so far:

Arduino uno R3 with MP3 player shield.
Amplifier is Y148.

I use one power source for both arduino and amp, 12v/3a.
I soldered wires on +/- barrel jack on arduino board and connected to +/- on amp (red/black wires)
Audio out from mp3 shield is connected to audio in by this brown mic cable. (I soldered wires to
appropriate pins in 3.5mm jack).
There are speakers connected and also relay switch as input.

It works!

However, the problem is this strange noise i hear that i can’t identify…
It appears only when audio source is connected. Amp it self is really quiet without source in.
NO buzz or any other sound, other than some murmur when volume potentiometer is turned…
The sound is kinda higher frequency, not deep buzzing usually related to amp…

Also, it may work for say two days without any noise, than suddenly it appears.
I really don’t know where to look. Please point me in right direction, but also be specific.
I don’t know how to read schema… I can clarify more if needed.

Thanks again.

[batarale]

I guess this is ground issue...

Any hint?

Edit: When i plugin in headset, not using amp at all, sound in nice and clean...

[wolframore]

Since it only happens with the amplifier/speaker and not with headset, it sounds like it's happening in the amp/speaker combo circuitry.

Audio amplifiers can be tricky... sounds like you're getting either ground noise or RF interference, could be impedance mismatch... some of them love to pickup noise from cellphones... this is why high-end audio circuits exists and circuits are engineered to reduce or eliminate interference. You will have to figure out what's causing this so you can try to counter it. The inexpensive modules work but not always designed to a high standard. It's art and science behind getting great results and sometimes very expensive. You will have to figure out what its worth to you.

So just simply speaking you will not get $1000 performance out of a small few dollar module...

[batarale]

Thanks for your response.

I tested with SF mp3 player shield which i burned up unfortunately, same sound appears.

It is totally erratic. It may work without noise for two days. Than suddenly it starts... Than, if it is noisy currently, it may stop when i disconnect any of diodes green/red...

On the other side, it may start only than, when either of two is connected :)

I see lot of projects on the net with similar setup, so i guess it is doable without some special engineering...

Don't need $1000+ sound :). When it works sound is great for my need. Looks like noise stops when song starts playing... if this mean anything.

Edit: When play starts, both diodes are on, so can this be anyhow related? What diode can do to noise reduction? I tried just turning both diodes on without play and noise disappears...

[wolframore]

Can you provide the sketch? Are you by any chance using PWM on those LED's?

Also can you let me know what wires you used on the brown mic cable? Did you ground the shielding for it?

[batarale]

Pardon my ignorance, but i don’t know how to create schematics…

I’m not using PWM.

In source cable i’m using two isolated wires to connect appropriate left/right audio out to audio in.
Currently, shielding (which is here third wire) is not connected to ground in audio jack. Just with experimenting i found that by not connecting it, noise does not appear.

Power is shared between amp and aruino/shield. Barrel jack in arduino is where i soldered wires to + and gnd and connected to +/gnd on amp.

Current setup is attached. I changed pins since i noticed that all other pins are HIGH no mater what i set in code. Probably player shield is using them, not sure…

However, only when both diodes are on, noise is gone. 24 hours up without noise
I know this is mess and looks ridiculous cuz i’m not sure what i’m doing

Appreciate your help!

Code:

#include <SPI.h>

//Add the SdFat Libraries
#include <SdFat.h>
#include <SdFatUtil.h>
//and the MP3 Shield Library
#include <SFEMP3Shield.h>

SdFat sd;
SFEMP3Shield MP3player;

int PIN_SWITCH = 3;
int PIN_LED_GREEN = 4;
int PIN_LED_RED = 5;

void setup() {

Serial.begin(9600);

pinMode(PIN_LED_GREEN, OUTPUT);
pinMode(PIN_LED_RED, OUTPUT);
pinMode(PIN_SWITCH, INPUT);

digitalWrite(PIN_LED_GREEN, HIGH);
digitalWrite(PIN_LED_RED, HIGH);
digitalWrite(PIN_SWITCH, HIGH); //turn on internal pullups for reed input

//Initialize the SdCard.
if(!sd.begin(SD_SEL, SPI_FULL_SPEED)) sd.initErrorHalt();
// depending upon your SdCard environment, SPI_HAVE_SPEED may work better.
if(!sd.chdir("/")) sd.errorHalt(“sd.chdir”);

//Initialize the MP3 Player Shield
MP3player.begin();
}

void loop() {

// Read the switch
int proximity = digitalRead(PIN_SWITCH);

// door closed
if (proximity == LOW) {
MP3player.stopTrack();
}

// door open
if (proximity == HIGH) {
MP3player.playTrack(0001);
}
}

[wolframore]

Could you try something... move the LED connections to PIN 10 and 11. On the original shield PIN 3 & 4 are taken by the shield.

[batarale]

Hi wolframore,

I tried, no trace of noise but only because both leds are HIGH, even if i set LOW on those pins. I will leave it as it is, on pins 4,5, since those are the ones i can control, will simply keep them HIGH.

So far it's good. I really dunno what is going on, but it works :)

Thank you for trying!

[batarale]

As my friend suggested, i added 2 100R resistors between GND/L and GND/R outputs in mp3 shield. Signal cable shielding is grounded. He explained something about impedance of player is different than amp input impedance...

Noise is gone and everything works as expected now...