PROJECT: Crossbar

[R.G.]

Yeah, I genned up a crossbar matrix out of the Zarlink 8x8 a couple of months back.

Works fine, as expected. No particular hitches.

Essentially all of the effort is in making up the user interface to tell it what to do. Fortunately I had a lot of that already in the can since my work on the ASMOP series a few years back.

Getting user interface that you understand this week is easy. Getting one that you understand in a year is hard. Getting one that a person who hasn't read the manual can do is... HARD.

[Chuck]

Thanks R.G.
The programming part for me is the easy part.
The circuit is the hard part, specifically keep the analog signal clean and fresh without loss.

Was there any noticeable tone or dynamic range loss?

Chuck

[R.G.]

No noticeable degradation until you hit the voltage limits, then it sounded unpleasant in a SS type of way.

Keep the signal level well under the specified peaks. I ran mine from +/-5V and signals up to over 4V peak had no problem.

If you don't do the -Vee supply, you'll have to AC couple and bias the AC inputs. I just ran it with bipolar supplies.

Standard practice for analog+digital chips apply - decouple power, watch where analog and digital ground meet, separate analog and digital signals, etc.

On the whole, it was an easy chip to bring up.

I found my stuff. I ordered chips after Ton's post here in early January. I got it running a few days later.

[Chuck]

R.G.
Wow, cool.  I'm about to order the chip.  Did you use the MT8808 or the MT8809?

Would you care to share a schematic, or is it a productin piece?

Your help is always amazing.  I have your relay based switcher working in my rack right now.
Chuck

[Chuck]

R.G,
Ok, I think I have it figured out -- using the MT8809.  I just have to use a 0.1 uF cap between the Positive Power Supply and the ground.

I was thinking if using two 74HC595A Serial input/ Parallel output shift registers with internal latch.

I can control the 74HC595A's using a PIC18F452.  Using this method, I would basically set the pins on a 74HC595A high or low and actually control the data, strobe and CS pins on the MT8809 by shifting pins, not using a clock.

By analog ground do you mean the ground on the effects loop jacks?
If I just connect the grounds from the 16 (8 in and 8 out) jacks -- I shouldn't have to connect that analog ground to the digital power ground at all right?

In the end the PIC receives midi events and sends a several serial commands to the shift register, which coverts these to parallel commands to control the MT8809.

Chuck

PS:  I'm a hobbiest, not a professional and I don't plan to market this as a completed device.

[Chuck]

Dang, I can't fnd anyplace to buy the MT8809.

Just the three models on Futurlec....

Does anyone know a source for the MT8809AE?

[Chuck]

Ok, I got the MT8816 Chip.  Arrived today.
I'm hoping to get some time this weekend to prototype something to see how it sounds.

Chuck

[Chuck]

Somehow I feel like I'm the only one in this thread anymore.

Ok, so here is a schematic using two Zarlink MT8816 analog switch arrays to switch any 16 inputs to any 16 outputs.  It uses a 8 audio buses between the MT8816s -- because to be honest I couldnt think of having ever needing more.

http://www.voodooengineering.com/release/Effects%20Router%20v01r.jpg
(Its a tabloid size drawing, but it prints well to letter size.  You may want to view it in a jpg viewer for a better look.)

The power supply and CPU is part of another drawing.  (PIC18 series microcontroller)

I know I didn't need two 74HC595 switch registers, but I was thinking about making the switching faster by switchng both 8816s at the same time.  R.G. spoke about grounding the amp out during switching.  I was thinking about taking one of the busses to do that.  I am sort of putting that off until later.

Here is where I could use some help.
Should I ground the audio jacks to the VEE, VSS or not at all?
I'm really hoping someone could respond to that question.

[David]

Chuck:

I believe you'll want your audio grounds connected together, but not to anything in the switching circuit.  Think about an ABY box.  You have two inputs on each channel.  One set of inputs is "selected" and connected to the output.  Otherwise, these connections shouldn't interact with anything else in the ABY circuitry.

[Chuck]

The MAX1044s arrived from Digikey today -- so now I can get the -5 volts..
And I made a new board, with a single 8816 setup for 8x8 routing.
I sent the board into ExpressPCB and it should be here Friday.  So we'll see....

I'm probably going to wind up with extra boards and chips for this if anyone wants to play.

Chuck

[Dave_B]

Somehow I feel like I'm the only one in this thread anymore.

Don't feel that way.  Some of these digital threads turn into journals.  That has a lot of value, IMO.  David was working on some MIDI pedals about a year ago.  I'm pretty sure it was just him after awhile, but I always checked in to see how the project was coming along.  Same with this one. 

[Chuck]

I'm trying to figure out a good way to connect the phone jacks to the pc board.
Normally I use PCB mount jacks, but 32 jacks is a lot of real estate.

I could wire each jack I guess.  I was hoping to keep everything modular since I'm just playing with this.  I don't look forward to making 32 pigtails for each jack.

I was thinking about making ( board with (4) jacks per board then using header pins and ribbon cable to link them to the main router board.  I like this best, but I'm not sure if it will be noisey.

Any suggestions?

[Chuck]

While I wait for parts and the board to be milled, I started working on the code.
R.G is right again though, the coding is going to take a lot longer then then putting together the circuit.

I drew up a front panel to have something to start with.

http://www.voodooengineering.com/release/FrontPanel.jpg
http://www.voodooengineering.com/release/RearPanel.jpg

In setup mode you need to:
Assign a name to an effect and an effect to an input or an output.
Assign effects to a position in a chain.
Name a chain.

The naming functions require being able to scroll through AlphaNum characters (Up/Down Arrow).
Using the left/right arrows to select the character positon.

In program mode you need to
Assign a chain to a Preset.
Save a Preset to one of four positions in a Bank.
I plan to have 32 banks of 4 presets each.

In Play mode you need to be able to:
Select a Bank  (Up and down arrow).
Select a preset within a bank (Left and right arrow).
Turn on and off an effect in a chain.  (Effect select buttons on the left)
Mute all outputs.
Use a Midi footcontroller.

In play mode the display shows you the chain and using a larger LED alphanum display show the Bank and Preset. ID.

I'm using a Rocktron MidiMate as a footcontroller for now.

I'm still working on the best way to jam 32 1/4 phone jacks onto a board and into a chassis.

This is all going to take a while.....

[Chuck]

Board is here and soldered.

http://www.voodooengineering.com/release/router1draft.jpg

This is an 8x8 version using a MT8816.  I wanted to start a little smaller then 16x16.
I have to work out the 1/4 jack mounts yet.

I have some tough work days ahead at my day job so we'll see you again next weekend.

[Dave_B]

Dang, that's purdy!  Chuck, I'm sure a bunch of folks will be interested when you fire this thing up.  Are you still pondering the µC part of it? 

Dave

[Nikolay]

What about analog device's AD75019JP
PDF here: http://www.farnell.com/datasheets/12530.pdf

This is 16x16 crosspoint array and first is more easy to find or take a free sample and second this replays the 2 MT8816 chips.

Just the idea.

[David]

Somehow I feel like I'm the only one in this thread anymore.

Don't feel that way.  Some of these digital threads turn into journals.  That has a lot of value, IMO.  David was working on some MIDI pedals about a year ago.  I'm pretty sure it was just him after awhile, but I always checked in to see how the project was coming along.  Same with this one. 

I haven't given up on them, either!  I have some stuff hangiing over my head that I have to handle first, then the pedal project is going to come back to life - bigger and badder than before.

[Chuck]

To be honest I just ran with the MT8816.  I have six of them now at $4.20 each.
The AD75019 looks cool. I like the serial control.  They are $22.00 each.
The AD75019 does look easier to draw up. 
Since I have a hadnfull of MT8816 chips I'll probably stick with this for a little while.

Chuck

[Chuck]

I haven't forgotten about this.  I just been busy with paying work.

I shall return!

[Chuck]

I got a ton of stoff done today.  Everything is all wired up to the midilab.  Now I can debug the code I'vee been noodling through.
In case you noticed, I am using board from midibox.org for the midilab.  Its just a development testbed...   I'm not marketing anything.
This is the 8x8 board I showed you earlier.  Right now there are only 4 jacks wired to it, because I'm not sure if the ribbon cable will introduce noise yet.

http://www.voodooengineering.com/release/lab1.jpg
http://www.voodooengineering.com/release/lab2.jpg
http://www.voodooengineering.com/release/lab3.jpg
http://www.voodooengineering.com/release/lab4.jpg
http://www.voodooengineering.com/release/lab5.jpg

Comments anyone?  Its wierd that there are thousands of views but no comments....