board to board bus - standards

[audiomixer]

Hi,

I have been working on my mixing console project and I am getting on with the analog boards design. thinking of the benefit the 51x standard has brought, any one inclined in sharing thoughts on a console bus wiring scheme?

I wanted to use a 34 / 40 pin ribbon cable for the bus and thought about a suitable arrangement for my console, but of course someone has done that already in the past so you might just chime in with your list.... would be fun to see how much common there is and if it could make sense to publish a spec that one can adhere if inclined to ;-)

attached is my first pass, 2main +4sub buses, pfl, solo, up to eight aux buses. reduced functionality with 20pin / 24pins.... no power, as I route power via a larger dedicated pin header.

 

[Rochey]

Awesome stuff!

But please, route USB (including digital power) and UART/MIDI.

Digital Control of Analog offers a massive amount of flexibility for those doing recall etc.

/R

 

[audiomixer]

all the controls are on a separate board.
on my mixer I opted for push buttons not switches. these are linked to an arduino with 128 I/O expansion. that allows me to control mute / PFL / bus switching for up to 16 channels. I believe I could add an other 16 channels with a second control board, but I have not tried. I could add USB and/or midi there, but on the audio bus ribbon cable I'd rather not..... I have no direct plan of enabling computer control of the switches, but it would be doable since the arduino can easily be connected to the workstation. I just haven't found that to be useful for me right now.

attached a picture showing the mock up with 16 channels muted (red swiches) one PFL active and some channels routed to bus A and bus B. In my mixer design all channels are routed to the main bus, and individual channels can be routed to two additional stereo buses. the idea behind proposing a standard would be to facilitate the use of others audio boards like hakanai's beautiful channels strips or his upcoming master section.  Spencer has posted some requirements for something quite similar just a few days ago. while not identical, we might speed up projects if we can reuse some designs. my desk should end up with a full featured master section eventually, but maybe someone would design something that would be suiting my needs before I can...

the switches are non latching and their respective state is shown via leds. It just happened I liked the look of the switches. The software controlled switches control either relays or fets on the audio board via a pin header. but I digress...

- Michael

 

[Rochey]

So.... the standard your proposing is a superset of your exact use case, therefor, it's not universal enough?

 

[audiomixer]

So.... the standard your proposing is a superset of your exact use case, therefor, it's not universal enough?

actually it is a superset by far, but otherwise I don't think anybody will take on it. two options are proposed right off the bat: use smaller pin count to reduce cost / size and some additional pins to be defined - I think some might want power on the same cable, and a few spare signals for pfl handling and the like. some quirks are specific of my design of course, like the symmetrical main bus...  in my opinion the design is sized for a full fledged diy console. I did quite a few live mixes with less buses in the past 

- Michael

 

[Rochey]

Well done. You just defined 500 and 51x.

Sorry, I'm not normally that b*tchy, I'm just sick of people thinking they are starting a revolution, then re-hashing the same stuff that we did 20 years ago.

Sadly, I do this sh*t for a living too

 

[Rochey]

ahhh... just re-read this. realized I was being a bit doushish.

To try and keep things more professional...
Let me provide some benefits to embedding a low power rails and a digital interface

- Digital Control and Audio Expansion become possible.
- Capability to integrate with DAW's for things like remote control and recall.
- Fancy LED/Relay switching all happens from the digital power rail, instead of the sensitive analog power rail.

Such capability looks 10 years into the future of groupdiy, instead of 20 years into the past.

 

[ramshackles]

You are running mono buses?

I'm following ruffrecords example with the eztubemixer, and using the eurocard format for a simple, discrete, modular mixer. Modules mate to a 3U backplane via a 32 way DIN connector.

My pinout at the moment is as follows:

1a In-              1b In+
2a In (screen) 2b In2 -
3a In2 +          3b In2 (screen)
4a 0V              4b Out 1
5a Bus            5b Out 2
6a Bus            6b Bus
7a Bus            7b Bus
8a Bus            8b Bus
9a Bus            9b Bus
10a Bus          10b Bus
11a Fader 0V  11b Bus
12a 0V            12b Fader send
13a 48V          13b 5V
14a -16V        14b -16V
15a +16V        15b +16V
16a 0V            16b 0V


The simplest configuration would be a single backplane with 3 stereo buses, 4 auxes and a stereo mix bus. You could duplicate the backplane over 6U and have the upper one dedicated to e.g. auxes and the lower one dedicated to mix buses. Of course, you could also use buses for other stuff...solo, logic etc.
Currently I have an EQ module, a mic preamp and a stereo summing module, so the exact configuration of the pinout could alter. Only pins 1-5b and 13a-16b are set in stone....

The modules are on 100 x 160mm eurocards, here is an example of an EQ in progress:

 

[ruffrecords]

I notice you have provision for up to 8 AUXes. I am curious, what would anyone use 8 AUXes for?

Cheers

Ian

 

[audiomixer]

thanks for your input

I did consider a backplane, but this is definitively not for me. it makes much more sense for functional modules, like yours, I agree. but then you do need a large and complicated (and costly) backplane with all the individual input / output routing. I was dwelling into a ribbon cable solution, that makes individual routing of independent signal (like your Module Input and to some degree your Outputs) almost not practical. I know it can be done, but it ends up in a messy dedicated cable harness and makes the IDC connection a lot more prone to failure. I have seen Dons solution with a partial backplane and headers to connect them to form a bus. I wonder if there was a common ground on a system like his...

I agree upon the possibility of reusing the buses for aux / main / surround as per ones personal taste. sure enough this is not to much of a problem, as long as bus is kept a bus. besides the main bus that is stereo and balanced for maximum performance beyond light speed all buses are mono, although my design will use them as stereo pairs. they are arranged so that one can choose the required bus size while still retaining basic compatibility. the basic bus count besides pfl / solo is 2 - 4 - 8 so you could easily implement a stereo master bus and up to four aux buses on the smaller 20pin layout.

I do agree somewhat with Rochey on the power / control issue. this is probably specific to some design decisions I made much earlier on: there already is a full fledged control bus with dedicated power for swichtes, relays, leds in my design so I have no need to put it on he same ribbon cable. It's part of the concept to fully separate audio and control. after thinking of usb as a comms solution inside the mixer I believe this would make things pretty ugly on the implementation side. USB is not readily daisy chained and I doubt that the overhead in programming a multi micro controller solution is a sensible thing too. my first design ideas where around individual micros on the switches pcb that talk to each other on a bus. now that I have 16 channels on a single Arduino I must say this made it much easier for me. programming was just a matter of reading the switches state and updating the outputs accordingly. I would plead for a I2c bus if you do need communication between modules.

I will rethink the arrangement so that it might fit i2c and power rails as default as well as some minimal signaling. any thoughts on individual 0V shield / ground wires between signals on a ribbon cable?

- Michael

 

[audiomixer]

I notice you have provision for up to 8 AUXes. I am curious, what would anyone use 8 AUXes for?

Cheers

Ian

good question indeed. to some extent filling up space up to 34pins on one side and ability to do a 8 bus system on the same pinout on the other. open for discussion ;-) subgroups and auxs are not necessarily dedicated functions as they are functionally equivalent on the bus at least.

- Michael

 

[Rochey]

I would plead for a I2c bus if you do need communication between modules.
I will rethink the arrangement so that it might fit i2c and power rails as default as well as some minimal signaling.
- Michael

Michael,

I like where you are going with this. Might I suggest a an ID pin that could tell the host wether the two digital pins are USB or I2C?

On the host side (i.e. your motherboard or whatever) you could have a simple Mux that is controlled by the ID pin.

I'll draw something up. My creative juices are flowing this morning.
Can you spare me 5 pins total?

 

[audiomixer]

here is V1.1 of the bus spec.

besides some tidying up I implement some of the discussed additional signals and added power rails for analog, phantom and digital supplies. plz have a look....

- Michael

 

[Rochey]

Michael,

from a board layout perspective, is there any chance you could put the digital stuff all at one end (after the PSU's?)
(pins 35 through 40)

Thanks again

Dafydd

 

[audiomixer]

Michael,

from a board layout perspective, is there any chance you could put the digital stuff all at one end (after the PSU's?)
(pins 35 through 40)

Thanks again

Dafydd

how about this?

- Michael

 

[Rochey]

Excellent,

I'm working on a method for the ID to switch the control method for either
USB
I2C
Midi TX/RX
UART RX/TX
As well as a standard interrupt line.

Just to be clear, is this for channel strip to channel strip, or from channel strip to main control system?

 

[audiomixer]

should span across channel strips, group and aux masters, and main summing bus of course.
all bus outs will be available on d-sub / XLR.

a monitor / CR section with multiple inputs will be on a separate board. still figuring out the specs....

- Michael

 

[ruffrecords]

here is V1.1 of the bus spec.

besides some tidying up I implement some of the discussed additional signals and added power rails for analog, phantom and digital supplies. plz have a look....

- Michael

What is the difference between 0V and AnalogGND?

Cheers

Ian

 

[audiomixer]

I wanted to provide a possibility to separate decoupling capacitors return currents from 0V reference.

- Michael

 

[Andy Peters]

USB is not readily daisy chained

I totally agree with this. If there's an intent to distribute USB to the various modules, then you need a USB Host (or OTG) controller in the master slot. This means at the least an ARM of some sort with mucho balls. To support distributing USB to the other slots, you have to connect your host's downstream port(s) to hubs, and then the hubs' downstream ports get routed to the slots, one port per. This is doable, although you must take care with the routing.

I haven't mentioned the world of hurt you'll enter when you need to consider the USB host driver stack. You might end up running Linux on your ARM. Congrats, you've now designed an embedded computer.

And to what end? What sort of thing will you have in your slots which make USB an attractive interface? It seems like a lot of overhead and complexity for very little gain.

I would plead for a I2c bus if you do need communication between modules.

I agree with this too. Every micro you'd want to use has at least one I2C bus interface, and I2C is multimaster, so if for some oddball reason slot 4 needs to talk to slot 5 it can do so. Of course you'd still want to have a master slot, and then that master slot needs to do something interesting that makes it a master. I can't see what that might be, except maybe it's got a host interface (USB? Ethernet?) back to some computer which does something interesting.

The thing with slot-to-slot communication is that now each slot needs to be aware of whatever is in the other slots, and know how they talk, and that's a level of detail I think that would need to be really thought through if it's to be useful. I mean, does an ADC module need to talk to, say, a preamp module or an EQ module? I don't see the utility.
-a