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Topic: Virtual, variable resistors, with saved presets recallable by MIDI (Read 16184 times) previous topic - next topic

Stoopalini

So far so good ....

Made a little more progress today, but on the hardware side this time.  I need to get it down to a reasonable size to fit inside the effect pedal.

Here's the current state.  I was able to get everything on the board, so just need to add the MIDI input jack and the breakout box I/O jack to it. 

The bottom side has jumper wires soldered in for the connections.  Certainly a circuit board would be preferable, but this will work for this project.




Stoopalini

I hooked up the Arduino to the effect pedal today and gave it a test.  When the pedal is operating on a 9v battery, and the Arduino off a 9v to 5v DC power converter supply (the power supply came with my arduino accessory kit), it works as designed.  Albeit, the guitar signal has noise injected, but it works to adjust LEVEL and DRIVE VIA the Digi-POTS, and saving & recalling presets is functional.

When I connect the effect pedal to the same wall wart feeding the 9v to 5v converter feeding the Arduino (using a Y adapter for effect pedals), the noise is so bad I can't even hear the guitar signal anymore.

Here is the power converter I was using.  I had the 5v output from this converter wired into the 5v and GND pins on the Arduino.



So, functionality wise, the design is working to: control, save, and recall the two parameters; so it seems I need to start work on the power supply solution.

I assume I should place ferrite beads on the 6 lines going from the Digi-Pots to the effect pedal PCB, but not sure how to spec out which ones to buy. And can I use 1, or maybe 2?  Or do I need 6 (one for each wire)?  Any help here would be great!

Also, not sure how to determine where I should be tapping into the power within the pedal for feeding the Arduino.  Is it worth trying to feed 9v into the VIN pin, by splitting the 9v power from the wall wart plugged into the effect pedal?

Grumpy_Mike

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When I connect the effect pedal to the same wall wart feeding the 9v to 5v converter feeding the Arduino (using a Y adapter for effect pedals), the noise is so bad I can't even hear the guitar signal anymore.
Sounds like you have grounding problems. Have you connected the grounds together of the two systems?

The problem with effects peddles is that they often have what is called "ground lift" resistors fitted. This means that the signal ground for the audio is not at the same potential as the ground for the electronics of the peddle.
I faced that problem when I built a common power supply for five assorted peddles for my son. In the end I had to make a separate mains power supply for each peddle built into a box.

Without a schematic for the peddle it is hard to be definitive as to what to do. The simplest solution might be to have two isolated power supplies and opto isolate the digital pots, but I appreciate that is not the most elegant of solutions.

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I assume I should place ferrite beads on the 6 lines going from the Digi-Pots to the effect pedal PCB,
I don't think that will do anything for you.

allanhurst

Remember my earlier comments on the floating earth which i suspect  your pedal employs..  so I suspect you'll need a floating psu.

What does the noise sound like ? Hum ? hiss ? warbling?

Allan.


Stoopalini

Sounds like you have grounding problems. Have you connected the grounds together of the two systems?
I used a Y splitter cable on the power source, with one side going to the effect pedal and the other side going to the 9v to 5v converter.  I assume this means they're sharing the same ground?

The problem with effects peddles is that they often have what is called "ground lift" resistors fitted. This means that the signal ground for the audio is not at the same potential as the ground for the electronics of the peddle.
I faced that problem when I built a common power supply for five assorted peddles for my son. In the end I had to make a separate mains power supply for each peddle built into a box.
Yes, I completely understand this.  I have a TrueTone 1SPOT power supply on my pedal board, because every lead on it is an isolated lead.

Without a schematic for the peddle it is hard to be definitive as to what to do. The simplest solution might be to have two isolated power supplies and opto isolate the digital pots, but I appreciate that is not the most elegant of solutions.
Understood.  I was hoping to find a solution that didn't require 6 more opticouplers though :(


Remember my earlier comments on the floating earth which i suspect  your pedal employs..  so I suspect you'll need a floating psu.

What does the noise sound like ? Hum ? hiss ? warbling?

Allan.
Ya, I remember ... I was hoping you'd chime in. 

The noise sounds like buzzing/hum.

I just tested with two 9v batteries.  One powering the effect pedal, and the other powering the Arduino setup by attaching the positive lead to VIN and the negative lead to GND.  This produced a whisper quiet signal and works great! 

Just need to figure out how to get this type of performance when using 9vdc power from the power supply.

Thanks guys, really appreciate your help.  I'm very pleased with the results thus far!

Stoopalini

As another test, I tried a battery powering the Arduino setup, and the 9vdc wall wart on the effect pedal, and it's also quiet. 

So does this mean I need to configure a floating power supply connection for the Arduino setup?  How can I accomplish that by tapping into the 9v alread going into the effect pedal ... or is that even possible?

Grumpy_Mike

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So does this mean I need to configure a floating power supply connection for the Arduino setup?
Yes it looks like it.

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How can I accomplish that by tapping into the 9v alread going into the effect pedal
Sadly you can't. By definition if it is already going to one piece of equipment it can't float with respect to another.

Maybe you could use an isolated DC to DC converter but they do produce noise, they are expensive and they might inject more noise than you have at the moment.

Read about them here https://www.digikey.co.uk/en/product-highlight/r/recom-power/book-of-knowledge

allanhurst

Sadly I concur with Grumpy_Mike - I don't think there's a neat fix for this.

2 wallwarts are a pest, but not terribly expensive.


Allan

Stoopalini

What makes a floating power supply, floating?  Could I build a small board to accept 9v from the power socket of the pedal, and create an additional floating power supply just for the Arduino?  

I run 7 pedals off the 1SPOT power supply I have now, but it uses isolated leads for every jack.  What goes into building an isolated lead?  Could I use the 9vdc coming in to the pedal to create an additional isolated lead for the Arduino?


2 wallwarts are a pest, but not terribly expensive.
Agreed.  If I need to plug two power supplies into the effect pedal when it's done, one for the pedal and one for the digital controls, then so be it ...

Out of curiosity, I just plugged the effect pedal and the Arduino into two separate leads on my 1SPOT power supply.  It definitely was not as noisy as sharing the same wall wart, but also definitely not as quiet as using two batteries.  

It's probably worth mentioning I also have the setup sitting on my desk, right next to a laptop that seems to have the cooling fan running constantly.  So some of the noise is probably being injected through EMI, especially with the effect pedal's PCB just sitting loose (ie: not in the metal pedal enclosure) on the desk top.


allanhurst

Isolated means no electrical connection between the parts. Deriving an isolated supply from another requires an isolated dc-dc convertor as GM suggests.

EMI may be a problem, but it's not your major one. Cooling fans don't make much electrical noise. The PC processor etc DOES - but not in the audio range.

Sorry

Allan

Stoopalini

Gotcha. Googling "isolated DC to DC Converter" is coming up with lots of results.  Is there an IC I could use for this, or is it more complex than that?

I'm finding things like "fly-buck converters"

For example, the Texas Instruments LM5160-Q1

allanhurst

My feeling is that this is a bit like your investigation into motor-driven pots....yeah, you could do it, but it's a lot of hard work which inessential to your project.

Allan

Stoopalini

I spoke to a buddy who is an electrical engineer at Flextronics, and also has a business making pedals and custom guitar circuitry.  He recomemded to try upping the input voltage to 12v, and using a 7809 voltage regulator for supplying 9v to the pedal's PCB and a 7805 to supply 5v to the Arduino.  It might not be enough, but for a couple of dollars, certainly worth trying. 

Parts are ordered, and I should have them in a couple days. 

Grumpy_Mike

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He recomemded to try upping the input voltage to 12v, and using a 7809 voltage regulator for supplying 9v to the pedal's PCB and a 7805 to supply 5v to the Arduino. 
I can't see how this would help with the problem at all from what you have described.

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Googling "isolated DC to DC Converter" is coming up with lots of results.  Is there an IC I could use for this, or is it more complex than that?
It is not just an IC but a method of designing the circuit and normally involves a transformer. You can buy ready made isolated DC-DC converter modules, the main consideration / cost being how much current you want to draw from it. Your peddle should not take too much current.

Much cheaper is two mains supplies which are isolated from each other by default. That is to say that all mains power supply are isolated from the mains and so will be isolated from each other. If you only want one lead then connect it to two converters inside the box.

allanhurst

OK - if you're determined to do it with one wallwart, the enclosed should work ..

Values for R3 and R4 might be a bit high - check for 5v across the arduino ( use the 5v pin) .

They must be equal.


regards.....


Allan

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