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Topic: Bluetooth Potentiometer Crackle (Read 523 times) previous topic - next topic

smclement57


So I'm working on a guitar pedal project that uses bluetooth. The hm-10, (bluetooth module), is constantly receiving data every 30 milli and then the arduino uses that info to control MCP41100 digipots. The only issue I'm having is that when the bluetooth is turned on you can hear either that data transfer or the stepping of the potentiometer, I'm not sure which. The guitar signal is clean until the bluetooth get connected and the potentiometer starts working. I'm looking for a way to quiet it down if anyone could help.

Grumpy_Mike

Quote
The only issue I'm having is that when the bluetooth is turned on you can hear either that data transfer or the stepping of the potentiometer, I'm not sure which.
So the first thing to do is to try and determine which it is. Once you have done that you can go about taking measures to prevent it.

So eliminate the blue tooth first, and replace it with a mechanical pot changing the digital one.


smclement57

I narrowed it down to the digital potentiometer today, but the project wont work with analog pots they need to be digital. Is there any kind of compressor circuit or something i could run it through to eliminate the sound the to pot stepping up and down? This is my first real project and I dont know too much about sound signals.

smclement57

After some scouring i've found this is called the zipper effect and it is infact due to the stepping of the pot. If anyone could help with any system of eliminating this sound itd be greatly appreciated.

al1fch

#4
Oct 03, 2019, 09:09 pm Last Edit: Oct 03, 2019, 09:13 pm by al1fch
Hi
Less or no zipper effect ?
Some digital potentiometers differ siwitching to signal's zero crossing and so offer reduced zipping noise. Here are  some ones  :
https://www.maximintegrated.com/en/products/analog/data-converters/digital-potentiometers/DS1882.html
https://datasheets.maximintegrated.com/en/ds/MAX5408-MAX5411.pdf

Grumpy_Mike

#5
Oct 04, 2019, 09:15 am Last Edit: Oct 04, 2019, 09:16 am by Grumpy_Mike
Well done in tracking it down. Yes the zipper effect is actually injecting noise into your signal. This is a specific high frequency and the only way to eliminate it is to use a filter. You could use a narrow notch filter tuned to the frequency of one of the clicks.

But much better is to "eliminate it at source", which means stop it being generated in the first place. So al1fch has the answer to use a digital pot that doesn't generate the noise in the first place. A pot that was designed for audio applications. Read the data sheet of any pot before you buy it. If it does not mention audio applications then you assume that it is not suitable.

smclement57

Thanks for the answers guys I'll give it a whirl and get back.

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