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Topic: Signal noise on Vcc using Catalex serial MP3 module (Read 777 times) previous topic - next topic

ee0u30eb

Hi all,

I'm creating a project with the Catalex serial MP3 player and I am controlling it using an IR receiver and IRlib library.

The issue i am seeing is that the IR receiver is constantly outputting signals as if there is a 38kHz signal present even though there isn't.

I have isolated the issue to the MP3 player which shares its Vcc and Gnd... powering it off stops the problem. I have tried adding a small cap between Gnd and Vcc to filter any noise but this doesn't seem to be fixing the problem. is there anything else I could do?

The circuit is at its bare bones right now... IR receiver hooked up to power and pin D11, mp3 module hooked up to power and pins D5 and D6, nothing else.

Thanks!

Grumpy_Mike

What IR receiver are you using?
Most recommend a 100R in series with the power rail and a 4u7F capacitor from the power pin on the IR to ground.

ee0u30eb

To be entirely honest I do not know... I pulled it from my scrap electronics pile. I have a few IR sensors and they are all exhibiting the same issue.

I'll try the resistor idea and get back, thanks for your help

ee0u30eb

Ok.. I have played with some values and found some that seem to work well (limited by what I have available right now). A 1uF cap from source to Gnd and a 68ohm resistor seem to blocking the noise out.

So if I recall correctly this is a high pass filter, where Fc = 1/ (2 Pi RC)

In which case I guess this blocks anything below Fc which works out as 2.3kHz

Is that correct? When I try to get values closer to 38kHz it doesn't work as well and I would ahve thought it should.

Thanks for you help, its really appreciated

Grumpy_Mike

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So if I recall correctly this is a high pass filter,
No it is a low pass filter.

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In which case I guess this blocks anything below Fc which works out as 2.3kHz. Is that correct?
No. The Fc is where the output drops by half, it continues to pass higher stuff at a lower and lower amount as the frequency increases.

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When I try to get values closer to 38kHz it doesn't work as well and I would have thought it should.
The lower you can make the Fc of the filter the better, not the other way round.

ee0u30eb

Just an update in case anyone else has the issue.

The noise came back from time to time and although I thought I had isolated the source, it turns out it was my overhead day bright compact fluorescent tube light causing the noise!

I'm not sure how best to avoid this apart from turning that light off - the problem this causes is that the IR loop executes over and over when the noise is there and slows down the rest of the program. The added noise also means that the IR signal isn't always read correctly and requires a few presses to get the right code.

Grumpy_Mike

Is this optical noise? That is does it go away when you cover the IR receiver?

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