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HC-05 and annoying pulsation

Thread starter #1
I'm using Arduino Uno + Hc05 within the guitar effects chain that is between guitar and amplifier. It happens that the blinking of the LED on HC05 is also transmitted to the output of the loudspeaker from which comes an annoying pulsation that I would like to eliminate.

In fact, if I power off the HC-05, the bluetooth switches off, the LED goes off and the pulse disappears.

I tried to put a 100 uF capacitor in parallel to the power of the HC05 but I did not solve anything and the pulsation remains.
 

cowboybob

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#2
I'm using Arduino Uno + Hc05 within the guitar effects chain that is between guitar and amplifier. ...
What device in the guitar effects chain is the HC-05 "talking" to?

It sounds as though the HC-05's "State" port output (PI08, used to drive the LED) is somehow getting into the audio stream.

A block diagram of your Bluetooth system would be useful. Or, better yet, a schematic.
 
Thread starter #3
Thread starter #5
At the top of the picture, there is the chassis containing the buttons, to the right there is the connector for the 9V plug that goes to 7805, screwed to the chassis and leaned on a button.

Always on the right but at the bottom of the chassis, there is the USB socket, secured with two-component glue, where I plug the cable that leads to the USB input of the effect. At the center there is Arduino (below) and the USB Host (above), all spaced from a plastic base, using 2 screws, also fixed with two-component glue.

On the left of the photo is the HC-05 and the switch that serves to disable bluetooth when I have to program Arduino.
 

cowboybob

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#6
I see.

Is the "pulsing" a recent problem? If so, did it follow an update of the Arduino software or a wiring alteration?

The solution might be as simple as disabling the HC-05 0n-board "State" LED (if you're lucky). How handy are you with a soldering tool and SMDs (Surface Mount Devices).

<EDIT 0923 EST> Also (sort of a SWAG) as an afterthought, the ground wiring arrangement(s) could be forming a ground loop back though the whole system (from the HC-05 all the way to the amp). This could be allowing the pulse(s) of PIO5 to be presenting at the output.
 
Last edited:
Thread starter #8
I see.
Is the "pulsing" a recent problem? If so, did it follow an update of the Arduino software or a wiring alteration?
no

The solution might be as simple as disabling the HC-05 0n-board "State" LED (if you're lucky). How handy are you with a soldering tool and SMDs (Surface Mount Devices).
I can try
<EDIT 0923 EST> Also (sort of a SWAG) as an afterthought, the ground wiring arrangement(s) could be forming a ground loop back though the whole system (from the HC-05 all the way to the amp). This could be allowing the pulse(s) of PIO5 to be presenting at the output.[/QUOTE]

I've been careful about wiring to avoid ground loop. It must be caused by the voltage drop on the LED
 

cowboybob

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#9
Put a cap across the led 104 would do.
Also a reasonable effort.

Although, noticed this addition at the State pin, which appears to feed another LED (or something) added in the stomp box:
upload_2017-10-2_9-26-1.png
Disconnect it at the PCB and see if that eliminates the "pulsation".
 

be80be

Well-Known Member
#10
If the led is some kind of blocking delay that could be a problem it be like keying a mic at a fast rate
 
Thread starter #13
I understand it depends on the power supply. If i use a power bank or a power supply with isolated outputs, I have no noise but the power bank is not a guarantee and the power supply with isolated outputs I do not have it yet
 
Thread starter #14
I put another power supply with multiple filtered but not isolated outputs and the pulse has stopped. For a moment I thought I was fixing the problem but now i feel more accentuated the same background hum of the amplifier.
 

cowboybob

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#15
I put another power supply with multiple filtered but not isolated outputs and the pulse has stopped. For a moment I thought I was fixing the problem but now i feel more accentuated the same background hum of the amplifier.
Sounding like a grounding problem again (if the background hum is 60Hz/50Hz, wherever you live). Try connecting a common ground in the stomp box to the aluminum shell housing. And make sure ALL the power supplies have a common, earth ground. One floating ground in a audio system (as you probably know) can make for a lot of HUM...
It's not the led it's the keying
Agreed, be80be. The LED is not causing the problem. The triggering of the LED does appear to be the problem in that it syncs with the "pulsation". Thus far, those square waves triggers (chock full of harmonics) are somehow worming their way into the audio system. The why is elusive but I'm leaning towards a grounding problem. Tough to do from a distance... :banghead:.
 
Thread starter #16
I tried with a wire to make the bridge between the aluminum enclosure and the chassis of another pedal and the noise is reduced but only a little but it does not cancel
 

cowboybob

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#17
There needs to be a continuous, unbroken ground path from all instruments, electronics and metal enclosures to earth ground.

Otherwise, spurious electrical noise will find its way into the system.
 
Thread starter #18
I have 5 pedals in the pedalboard, 4 analog and one digital and to eliminate the ground loops I connected the 5 pedals in parallel with the same power supply using a daisy chain like this
http://guitargearfinder.com/wp-content/uploads/2017/03/guitar-pedals-daisy-chain.jpg
but, important, leaving the positive and the negative only to a stomp box, while to other pedals I cut the mass, leaving only the positive pole, so the stomp boxes take the ground from the jack connections. If i try to put the ground back on the power of all the pedals, I think it would be like you suggest doing but so the noise is stronger
 

cowboybob

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Most Helpful Member
#19
Given the complexity of your system, I still suspect a grounding problem, especially since:
... while to other pedals I cut the mass, leaving only the positive pole, so the stomp boxes take the ground from the jack connections...
My emphasis.
Not good enough.

For the sake of the argument, just try running a ground wire from a known system earth ground (amp chassis?) to the ground connection of the power jack on the stomp box.

Actually attach it, not just hold it in place with a finger.
You, too, are a ground of sorts, but allow an antenna...
 

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