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### Topic: Crosspoint Switch (Read 2635 times)previous topic - next topic

#### MattiasOfTheMetal

##### Sep 17, 2012, 11:18 am
Hi! I have lurked the forums for a while and searched google thoroughly for the past few weeks, and this is my first post on a forum (ever), so bear with me. I felt it fell into this category rather than audio, but if a mod could move it if I am wrong then I would appreciate it.

Ok, so my goal is to incorporate an 8x8 crosspoint switch into a guitar. I plan to route a pin to each + and - of each coil (two humbuckers). I have read up that a guitar signal can be less than 100mv up to 1v. I've always heard it was < 0.3v, so I'm going to run a volt meter aside my guitar signal tomorrow to verify my max voltage swing.
I have found a few chips that seem possible for me to use, the MT8809 (http://www.zarlink.com/zarlink/MT8809_DataSheet_Sept11.pdf), and the MAX456 (http://pdf1.alldatasheet.com/datasheet-pdf/view/73393/MAXIM/MAX456CPL.html).

They both seem to have really low capacitance, not much crosstalk, but their voltage swing for the io pins are +/- 0.3v, which could potentially be a problem.
From looking at the datasheet of the mt8809, it seems easier to interface rather than the max456 due to the address table on page 7.

That is only one part of my scheme.
The other, is that the guitar will be phantom powered over a regular 1/4" cable, 2 conductor (mono), meaning the + and - signal for the guitar which is an AC voltage, will also carry 9v DC. (I already have that part done)
My question is, is that if there is 9 volts on that signal, how may I remove that DC voltage from the signal onboard the guitar to not fry the cp switch while still powering my arduino and the other goodies I'm adding to it?
So the cable would carry the signal and 9v, then send only the 9v for the onboard arduino, and only signal to the io pins of the crosspoint switch/pickups.
It almost seems it would be easiest to just have a crosspoint capable of > 9v... *sigh*
I would appreciate it if anyone can give me some insight. I have not bought the chip yet, I'm still searching for the right one.
Food for thought.
Nom.

#### MattiasOfTheMetal

#1
##### Sep 17, 2012, 10:17 pm
I have come up with a simpler idea since I posted last, and it is more efficient. However, on my guitar's pedalboard, I was planning to use a cp switch on that as well, which I don't see a simple way around without building my own switch matrix.
I have two questions though:
1. If I do use a cp switch, since most are limited to +/- 0.3v, is there any way to increase the max/min voltages or work around them?
2. If I don't use one, what kind of switch could I use? I was originally thinking transistors, but they are polarized, are they not? And I don't wish to add any gain to the signal. I also looked at optocouplers, but I've never used them before.
If anyone can point my in the right direction, I'd appreciate it. =]
Food for thought.
Nom.

#2
##### Sep 18, 2012, 01:29 am
Quote
I was originally thinking transistors, but they are polarized, are they not?

FETs?

Quote
It almost seems it would be easiest to just have a crosspoint capable of > 9v.

ADG5204, ADG5208/5209, ADG5233/5234, ADG5236. But AFAIK they all need dual supplies if you want to switch AC. This could be generated locally with a DC-DC converter though. For DC they go to 40v or some such.

______
Rob
Rob Gray aka the GRAYnomad www.robgray.com

#### Docedison

#3
##### Sep 18, 2012, 07:15 am
For low level up to +/- 7.5V CD4016, 51, 52, 53, 66,67, 97 and CD4516 are all low current analog transmission gates. I enclosed a CD405X data sheet it covers the '51, 52, 53...
Just an Idea.

Doc
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"The solution of every problem is another problem." -Johann Wolfgang von Goethe
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#### MattiasOfTheMetal

#4
##### Sep 18, 2012, 08:12 am
Thanks for the input,
I looked at those chips, and I couldn't find any that weren't surface mount.
I was interested in those few that were IC switches, could be useful.

@Doc
I appreciate the help,
If I'm reading right on the datasheet you attached for the CD405(x) series, the max voltage to pass through a pin is 15vdc, but I don't see anything about ac. And it looks like the min voltage it can handle is 0v, to the voltage supplied to it. I'd have to run it directly off 9v, and command it with 5v from the arduino, for it to handle the 9v dc power, but what would I do about the ac signal?
Food for thought.
Nom.

#### TonyD

#5
##### Sep 18, 2012, 11:31 am

If I'm reading right on the datasheet you attached for the CD405(x) series, the max voltage to pass through a pin is 15vdc, but I don't see anything about ac. And it looks like the min voltage it can handle is 0v, to the voltage supplied to it. I'd have to run it directly off 9v, and command it with 5v from the arduino, for it to handle the 9v dc power, but what would I do about the ac signal?

You need to think about biasing (i.e. giving it a DC V level to sit on top of) the AC signal if you want to pass the full AC signal (positive and negative cycle) through the 4051 working on a +9V single supply rail.

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