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1  Using Arduino / Networking, Protocols, and Devices / Re: Connect to linvor on: October 01, 2013, 09:47:36 am
I have quite some expertise on the linvor and am happy to try to help, but maybe this problem is already solved?

Let me know if you still need help.

By the way, the linvor is only good for the most basic of bluetooth comms and it generates tons of EMI, so don't expect too much from it.

I have now swtiched to a Sparkfun BlueSRMIF which is far far superior in all respects.

2  Using Arduino / Project Guidance / Re: Electric Guitar Controls via Arduino on: September 30, 2013, 10:03:03 am

This has progressed very very far, thanks to this forum and many others!

Forget relays, though...

Check out my full detailed reports at my website , and also a little write up I got in HackADay.

I've spent lots and lots of time on it and the result is really really cooooool!

Let me know what you think!
3  Using Arduino / General Electronics / Re: Bluetooth and Arduino Electromagnetic interference question on: September 29, 2013, 03:57:29 pm
Well friends, I have spent now probably over 500 hours on this problem and have come to a new hypothesis.

The whistling was due to lack of shielding on the JY-MCU BT module - what do you want for 4€.

My spanking new Sparkfun BlueSMIRF with the shielded and certified RN42 bluetooth radio is quiet as can be!

Using a home made RF stethoscope, I found that the clicking at each data exchange seems to be the passing of the 5v square waves on the RX/TX lines.

Since the Bluesmirf is connected by a shielded cable, I doubled the shielding with copper mesh and then tin foil, and the clicking is practically gone.  It seems to be radiated from ever millimeter of exposed unshielded rx/tx line.

So, I now believe that housing the rx/tx lines and the bt module in a Faraday cage will eliminate all the clicking. As the circuit board stands today, this is not possible, but even with the shielding I was able to do, the noise is practically gone!

Also, I'm going to run the Bluesmirf at 3.3v instead of 5v to reduce the amplitude of the square waves.


The moral of the story: Square wave pulses cause EMI !
4  Using Arduino / General Electronics / Re: Bluetooth and Arduino Electromagnetic interference question on: September 10, 2013, 01:26:16 pm
Hello ArudGuitar fans!

Here's what may be the last report on the noise issue.

After carefully separating the audio and arduino grounds, installing the Sparkfun BLUESMIRF BT module running aty 115200 Baud, and using shielded wires wherever possible here's what we can say:
  • the BT whistle is far less than before, it is still present, but not noticeable when playing the guitar in normal circumstances
  • the data clicking may be "popping" of Vactrol LEDs or just surge into the amp when a pickup is activated.

For PWM pins, the Stackexchange electronics forum ( came up with a suggestion of stepping the PWM values, instead of jumping, so that the differences are less and there is less surge. THIS WORKED to reduce the popping, even remove it completely! But only for the PWM pins, not for the digital out pins which turn on/off the pickups.  Another suggestion using an RC damper( to prevent surge on vactrol LED had no effect.

So all that remains is to possibly try the following inductor filter circuit on the VCC/GND of the Bluetooth module to see if that can reduce the whistle....

Unless someone has an idea ;-)

5  Using Arduino / General Electronics / Re: Bluetooth and Arduino Electromagnetic interference question on: September 03, 2013, 01:06:35 pm
Well fans, I am back and baffled by the latest news.

I just deployed a new Sparkfun BlueSmirf BT module based on the Roving networks RN42 shielded bt circuit.

The result is better but not great:
  • the whistling noise is only slightly  less pronounced, but does not switch off after 10 seconds like it did on the JY-MCU
  • the clicking noise is greatly reduced, but still present

So, I am at the end of the road. Unless any of you very helpful arduino forum friends have an idea? grumpy_mike, are you still out there?

In any case, I will be showing the ArduGuitar at the  Kerkrade Maker Faire this coming 7 & 8 Sept. So if you're in the Netherlands and want to drop in, please do!

Thanks to everyone!
ps. you can still make suggestions for how to get rid of the noise ;-)
6  Using Arduino / General Electronics / Re: Bluetooth and Arduino Electromagnetic interference question on: September 01, 2013, 06:42:12 am
Hello all you dissatisfied DSO-Nano owners (and I'm one of them ;-)

No question about it: the 100€ spent on the DSO NANO was money for junk....

But, let me get back to the thread.

As you know, I have been struggling with a whistling noise induced on the opto-isolated audio circuit of my Arduino+Bluetooth+Android controlled electric guitar.

After lots of attempts at reducing the noise, the current situation is as follows:
  • The audio circuit is now fully opto-isolated from the arduino & bluetooth circuit: no common grounds, nothing touching, absolutely nothing,
  • The shielding has been reviewed and all potential ground loops have been removed,
  • Although 0.1µF caps were tested at points between Vcc and Gnd, these did nothing and were removed.

The result is that the whistle noise is reduced, much reduced!

But an annoying clicking is now very present - perhaps it was always there, but drowned out by the whistle?  The clicking is only present during data transmission from the Android to the Arduino; as soon as I stop interacting on the phone, the clicking stops. This was not the case with the whistle which only stops 10 seconds after interaction has ended.

Any ideas on what that could be?

It finally occurred to me to talk to a bluetooth expert and the tech support at Sparkfun pointed me to Roving Networks ( These guys manufacture industrial quality wireless solutions, including the RN42 bluetooth circuits used in the Sparkfun line of bt/serial modules. both Sparkfun and Roving tech support were fantastic. Once I gave Roving the info on the JY-MCU they were able to explain that it is neither certified nor shielded and that explains why the noise leaks so strongly.  So, in the end, the JY-MCU is really just more cheap junk (but still worth 4€ if you aren't concerned with being legal and noise...). 

By the way, the Sparkfun bluetooth tutorial and the Roving networks advanced user guides are great sources of info and inspiration!

I am now waiting for the arrival of a RN42 based "Sparkfun BlueSmirf Silver" module which is both certified and shielded!

Hopefully, this will be the end of the tunnel.... a report will follow later this week.

Thanks to all!
7  Using Arduino / General Electronics / Re: Bluetooth and Arduino Electromagnetic interference question on: August 31, 2013, 04:41:27 am
Hi Mauried!

I don't know the frequency of the whistle, alas. (I have a DSO NANO oscilloscope but that hasn't been able to measure anything, or maybe I just don't understand how to use it???).

In any case, I can tell you what happens.

  • after powering up the circuit, all is quiet, even though the BT module is on and is connected to another device (PC or Android phone)
  • as soon as a device sends data over bluetooth the whistle begins,
  • after the device stops sending data, the whistle continues for exactly 10 seconds, then stops.  I assume that this is the BT module going into some low-power sleep mode
  • this cycle repeats at every data transmission

I have recently been in contact with some bluetooth experts from who tell me that the JY-MCU is not at all shielded, as is normally required by law for all BT devices, and that it is not "certified" as a consequence. Naturally, all the Roving Networks bt modules are legal and certified and thus shielded.  By shielding, they refer to the clock circuitry, not the antenna.  The people there, and also at Sparkfun, think there's a good chance that using a higher spec bt module will make a huge difference.

I am now waiting for my RN42 bt module to arrive (Sparkfun product: ).

I will report on the result!

Thanks, Mauried, and thanks to everyone who has helped in this !
8  Using Arduino / General Electronics / Re: Bluetooth and Arduino Electromagnetic interference question on: August 30, 2013, 02:57:31 am
In the meantime, I've ordered a Sparkfun BlueSmirf silver module, which is based on the Roving Networks RN-42 bluetooth circuit which I hope is shielded. Roving says that their modules are used in electric guitars with no problem...

Hopefully, this will resolve the issues, but maybe not.

As an experiment, I held the guitar cable near my logitec bluetooth mouse. The result was the same whistle noise.

The problem with 433Mhz or other radio links is that I would then have to connect it to my android phone and make the whole unit a lot less practical...

Thanks for your suggestion!
9  Using Arduino / General Electronics / Re: Bluetooth and Arduino Electromagnetic interference question on: August 29, 2013, 04:19:42 am
Dear All,

After all these months trying to understand how noise from the JY-MCU bluetooth module gets into my guitar's amp, I finally, and embarrassingly, did a simple test.

I powered up the arduino and JY-MCU and connected via BT to my smartphone.

I took just the cable from the amp, not connected to the guitar or to anything else, and this is a specially shielded coaxial cable that cost a small fortune, and held it near the JY-MCU.  The result was the characteristic BT whistle.

My conclusion is that the JY-MCU is just a really noisy piece of hardware in the electromagnetic spectrum that the guitar's audio circuit can capture, since the whole thing acts like an antenna.

So, this brings me to ask you all: How can I communicate with my arduino, wirelessly without leaking electromagnetic noise?
  • Use a different BT module?  any suggestions?
  • Try a WiFi shield or module? any suggestions?
  • Try Xbee or other radio frequency module? any suggestions?
  • Other ideas?

In any event, I think that we can conclude that the JY-MCU is not the right choice for audio applications!

Thanks everyone, again, for helping me to get to the bottom of the problem !

Thanks to all of you who may have a solution to propose!

10  Using Arduino / General Electronics / Re: Bluetooth and Arduino Electromagnetic interference question on: August 29, 2013, 02:42:25 am
Hi Winner!

Thanks for your contribution!

I have already tried running the BT serial at lots of rates up to 115200 baud with no difference on the whistle, alas.

If I connect a USB cable and run the serial comms via the wire there is no whistle.

So the hunt continues ;-)

Thanks for your help - *all* suggestions are more than welcome!

11  Using Arduino / General Electronics / Re: Bluetooth and Arduino Electromagnetic interference question on: August 28, 2013, 10:26:00 am
Well, after yesterdays success, comes today's failures.

Everything I found yesterday seems to be a bit false today.  The no-noise setup caused by separating the power supplies for the arduino and the JY-MCU had no effect today!  The BT whistle is back but NOT as bad as ever... 

I have discovered that it is now reduced.  I attribute this to the separation of the audio and control circuits and careful attention to shielding.

Nonetheless, the BT Whistle is still present while BT comms takes place and for exactly 10 seconds after the last communication.

I am pretty convinced that the remaining noise is captured via the guitar pickups...

I ask you all, again, I know, any thoughts?

12  Using Arduino / General Electronics / Re: Bluetooth and Arduino Electromagnetic interference question on: August 27, 2013, 04:12:33 pm
Hi Polymorph,

Thanks for your tips.

However, I'm fighting against hum and noise from the Bluetooth module, not PWM.  In fact, I get the BT whistling even if there is no PWM.

Please excuse my ignorance, but how exactly would I connect the 0.1µF caps to my circuit? I don't know what you mean ...

Thanks so much,
13  Using Arduino / General Electronics / Re: Bluetooth and Arduino Electromagnetic interference question on: August 27, 2013, 09:04:42 am
Yo Team!

I had a "Eureka moment" just now!

After trying all sorts of things with capacitors to filter the BT whistle, and keeping the vactrols in a faraday cage and using all shielded cables I concluded this:
  • without common ground, there is too much hum getting into the audio part of the ciruit
  • with common ground, the BT whistle is present

So I thought suddenly, what if I power the BT from a separate power supply?  This may not work since the JY-MCU still needs to have a common ground with the Arduino as a basis for its serial IO... But why not try it anyway?

So I connected a L805CV 5V regulator to a 9V battery and used the +5V output to power the BT module; I connected the L805 ground to the Arduino ground, ie. the common ground everywhere including the guitar aurdio...  I powered the Arduino also from the 9V battery and...
... and ...
... and ...

NO NOISE!!!!!  YES! An Incredible result!

But how to explain it?

I also tried not connecting the circuit to the guitar, but keeping it very close, and using a mechanical pot instead of the vactrols. There was no BT whistle.

I can only conclude that somehow the BT module was inducing a signal into the Arduino's ground and that this was bleeding into the ground of the guitar.  But then when the +5V supply to the BT module was provided by a different source, not the Arduino +5V out, then the signal was no longer carried to the ground ?

Does anyone out there have an explanation?

I will continue to experiment, but I am going ahead with a second prototype installation in my ArduGuitar!

14  Using Arduino / General Electronics / Re: Bluetooth and Arduino Electromagnetic interference question on: August 26, 2013, 03:08:02 am
Hi not-so-grumpy-mike and everyone else!

I'm sorry for the long silence but I'm back now ready for more fun!

I guess the last time we were trying capacitors across the LEDs? I will do it this week and report.

You asked if PWM impacted the noise: no the noise is the same with or without PWM.

Do we have any ideas as to how the BT signal gets into the opto-isolated audio part of the circuit? Are the vactrols acting as antennae? Might it help to shield them?

Any new thoughts?

Thanks again!
15  Topics / Science and Measurement / Re: DSO Nano V3 - not impressed on: August 01, 2013, 03:40:01 am
oh, you're right! 

I have no solution. 

I regret even more buying this stupid device....

BUT MAYBE SOMEONE FROM SeedStudio will read this and make a new firmware that actually works!!!!!

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