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Making an existing EQ digital through Wiring Board (Read 10312 times)
04/11/07 at 03:34:35

Gr8Scott   Offline
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I have a project I would like to do, but I'm totally new to the Wiring language and also to the electronics side of things as well.  I'm good with a soldering iron and I can read schematics.  I'm also a very fast learner with most things.  What I really want at the moment is guidance from those who have any level of experience.

I want to take an existing stereo EQ that has a small footprint and turn it into a digitally controlled EQ with 16 memory presets that are changed using an ethernet (cat 5) network cable.  What I'm thinking of doing is removing the existing EQ sliders from their solder points and wiring the audio paths of the digital pots in their place.  I've found a I2C controlled digital pot (DS1882) that seems to fit my needs, but the price is steep for each unit ($11 each unit) and I'll need 8 of them.  The I2C chips have 3 pins for ID, which means I can use 8 digital pots max using that type chip.  I plan to piggyback the ethernet cable into this unit (the existing control network is a closed loop and there are no more available places to add a cable etc.  I don't want this unit to communicate on it's own and I basically want it to change to it's own internal corresponding preset number from the ethernet line and not try to send output to the other items.  I want it to be a silent accessory that the existing network is unaware of. 

Possible?  What will be the toughest part?  Other than the I2C pots, cat 5 splitter, EQ and Wiring Board what else do I need?  Is I2C the way to go or is there a better alternative.

The choice of using the ethernet cable is something I can't change.  It HAS to be done using that.  If I could change it to USB port etc, I'd do it for sure, but I can't.  I do wonder if I could use a ethernet to USB converter and still make it work?  Not sure...  I've hacked the CVS digicam with a USB cable before, so I'm familiar with how USB works.  Cheesy

All help/guidance will be immensely appreciated.  Cheesy
Gr8Scott
 
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Reply #1 - 04/11/07 at 22:24:53

barragan   Offline
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hi, well I am not an expert on EQs but what you are proposing sounds reasonable. You're right about the Digital potentiometer DS1882, you can connect up to 8 to the same bus, the address can be set using the pins or with the command byte as specified in the datasheet http://datasheets.maxim-ic.com/en/ds/DS1882.pdf
There is an example that might help you as well, using the I2C, and includes the code for setting the address of the device http://wiring.org.co/learning/examples/SFRRanger_reader.html for such device. There is also an example using another digital pot http://wiring.org.co/learning/examples/digital_potentiometer.html but for sure the one you're proposing will work fine. I'd suggest you to try make small tests with one and then just replicate your findings. If you can post more details that would help.
 
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Reply #2 - 04/12/07 at 04:38:41

Gr8Scott   Offline
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barragan wrote on 04/11/07 at 22:24:53:
hi, well I am not an expert on EQs but what you are proposing sounds reasonable. You're right about the Digital potentiometer DS1882, you can connect up to 8 to the same bus, the address can be set using the pins or with the command byte as specified in the datasheet http://datasheets.maxim-ic.com/en/ds/DS1882.pdf
There is an example that might help you as well, using the I2C, and includes the code for setting the address of the device http://wiring.org.co/learning/examples/SFRRanger_reader.html for such device. There is also an example using another digital pot http://wiring.org.co/learning/examples/digital_potentiometer.html but for sure the one you're proposing will work fine. I'd suggest you to try make small tests with one and then just replicate your findings. If you can post more details that would help.


Thanks for the links.  That will help me immensely.  If I use the command byte instead of the pins, how many different units can I use?

I'll be happy to share details.  I'm usually not encouraged to share lots of details because I make very long posts with way too many details that most people could care less about.

Here goes.

This is for two Vox Valvetronix AD120VTH heads I own.  This guitar amp is phenominal, but needs a little help EQ wise through the effects loop to sound correct at times.  Different guitar speakers sound best with certain amp models and not so good with the others.  With this programmable EQ, I can make the EQ attempt to correct for the speaker type through the effects loop.  This will make my clean fender and VOX models sound as nice as the Marshall models.  The VC12 stores whole banks of patches etc and sends the whole shebang to the amp etc.  It will store the current set of patches in the amp as well.  Because of all the intense com going on between the two, I figure the CAT5 cables are used in a more or less standard ethernet config.

This amps and controller pedal use the CAT5 cable to communicate with each other.  The VC12 controller has two CAT5 ports, but both amps will take up both ports.  I thought about splitting off the CAT5 cable or hacking into the amp itself, but I'll pick up a Netgear 4 port hub instead.  That should allow me to mirror the communications between the amp and the pedal to the EQ's.  I'm just hoping that putting the EQ's online with the amp and pedal won't cause issues with the amp or pedal working properly.  Same concern with the hub to be honest.  I think the Ethernet side of things will be my largest problem.  I need to make the wired board use ethernet.

I'll need to find an ethernet monitor program to see what the output from the pedal is.  This is what I want to program the EQ to respond to.  The amp/pedal has 4 banks and 4 patches.  I expect the com between them to primarily be some sort of patch change command followed by a 0-3, 0-3 of some sort.  It could literally say Patch 3,2.  The EQ will then read that Patch 3,2 is engaged and pull up the EQ settings from memory location 3,2 and send the appropriate commands to the pots.

The reason I want to do this project is that no product of this type exists for the Vox amp.  The improvement in the sound of the amp will be quite significant.  Not that it sounds bad as is.  There's always room for improvement.

I've thought about using the original sliders elsewhere as analog inputs for the EQ.  This would allow easy editing and the option of switching to analog control of the eq when needed.  I've thought of having a sort of global EQ change command to remedy the EQ for different locations.  Rooms with lots of clutter probably won't work well with tons of bass and will sound muddy in such an environment and a global cut of bass and boost of the mids would go a long way to make the guitar sound better in such an environment.  Of course, the global change is a temporary change.  Probably throw an analog, global and write button on the front.

Is I2C the way to go here?  Is there a better alternative?
 
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Reply #3 - 04/16/07 at 01:17:58

barragan   Offline
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hi, seems like you can use up to 8 units pero i2c bus, which seems limiting since you could use up to 128 devices in the same bus, there must be some other reference which enable you to do it, but the DS1882 has 2 potentiometers on it, so with 8 of them it will be 16 pots. The other thing I was looking at is that the DS1882 has a CE line which enables/disables the bus for that particular chip, if you control that line with a wiring digital pin you could have different chips sharing the same address by anable and disabling the chip appropriately. I think the best start is get one and just give it a try.
 
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Reply #4 - 04/22/07 at 04:04:31

Gr8Scott   Offline
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barragan wrote on 04/16/07 at 01:17:58:
hi, seems like you can use up to 8 units pero i2c bus, which seems limiting since you could use up to 128 devices in the same bus, there must be some other reference which enable you to do it, but the DS1882 has 2 potentiometers on it, so with 8 of them it will be 16 pots. The other thing I was looking at is that the DS1882 has a CE line which enables/disables the bus for that particular chip, if you control that line with a wiring digital pin you could have different chips sharing the same address by anable and disabling the chip appropriately. I think the best start is get one and just give it a try.


The EQ's are seven band stereo units with a gain knob (yet another potentiometer) which brings me to a total of 17 pots needed per unit.  If I can switch them all off via a digital pin that I can activate, I can use another 8 units on another board to operate the second unit I plan on building.

THANKS SO MUCH!  I'll get on it when I can.  Other projects are taking precidence for the next few months.  I'll get on this when those are completed.  I'm in the investigatory phase for now.  I really can't wait to get on this though as I now have two amps ready for the EQ units and a clear path of how to make them operate thanks to you.
 
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Reply #5 - 04/23/07 at 12:18:46

Gr8Scott   Offline
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Whoops!!!  I was tired when I wrote that.  The total needed pots for the EQ will be 15.  14 will need to be double sided and single control bringing the total down to 7 double sided and 1 single.  That's what those digital pots do best.  Smiley

Thanks again Barragan for the help.
« Last Edit: 04/23/07 at 14:00:17 by Forum Admin »  
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