Bus powered MB64E with core32?

[findbuddha]

Would it be possible to use USB bus power for a MB64E (or MBLC with encoders instead of motor faders) with the Core32?

Thanks

[lylehaze]

Would it be "possible"??

Sure, anything is possible.

It might even work!

But it would almost certainly violate the USB specification.

If I remember right, any USB device may draw up to 5 volts at 100ma (or was it 50ma?) without any problems..

the USB bus MIGHT be able to supply up to 500 ma, BUT ONLY if the device asks for it and the request is approved by the host.

And here's the part most people miss completely.. it is the responsibility of the DEVICE to not draw more than the above limits,

and to shut ITSELF down if the request is denied. SO if you draw more than 100ma without making a request for more and WAITING

for that request to be approved, you are in violation of the spec.

And if you EVER draw more than 500 ma, even if you go through all the Request/approval stuff, you are in violation.

Does it matter? Depends on what you plan on doing with it, and if you plan on sharing it with others.

Have Fun,

LyleHaze

[Flemming]

Never thought of it that way... but ofcourse there is a limit to what the USB can handle

I have one of these and it runs from the USB just fine, but that doesn't mean that it draws as much juice as a Core32 would, i guess.. even considering it's comprehensive logic, blinken lights and 2 huge LCDs

Maybe the manual will tell something about it's 'appetite'... i really should take a look

[lylehaze]

You may note that I never said how much a core requires, nor how much an MB64E needs for current.

The only reason I know what I do about USB is because I have written a driver, and worked with the developer of the USB stack to iron out a few bugs, including some that are power related.

A LOT of early USB ports on computers are wired straight to the +5 volt supply. there is no current sensing, and certainly no means for the USB stack to switch power on and off.. On a rig like this, you can draw power until the wires melt. (Of course the voltage will drop a bit as the wire heats up)

So a lot of people assume that because it worked for them.. it will work for everyone.

Now, just teasing the demons: How many MIDIBoxers are actually willing to measure the maximum current draw on their project?

I'm guessing most will just find something that works and stick with it.. and if it's just for you, that's fine! The MMA will not come knocking at your door because you didn't ask properly for the 500ma max current.

But on the other side, a lot of MIDIBox projects are pushing professional grade.. and if you want to CLAIM that your rig is USB powered, you may want to know what that would really require.

Yeah, I know.. too much detail.

Maybe someone learned something useful from all this, anyway.

I need sleep.

LyleHaze

(more detail.. a full MB64E will have 128 digital inputs(64 encoders), each pulled up with a 10K resistor.. that works out to 64 ma of current right there... assuming we need to stay under 100 ma, we have spent 2/3 of the power budget before we have powered up a single chip.)

Edited January 21, 2010 by lylehaze

[findbuddha]

Hmmmm, thanks for that :)

It'd only be for my use, so I don't mind if it violates the spec as long as nothing melts or releases magic smoke.

The core32 page on ucapps.de recommends a power supply of at least 500ma, but doesn't go into detail about what peripheral boards that might be enough for, or whether it can get that over USB.

Perhaps Tk would be able to help us out here :)

[seppoman]

Another thing to be aware of: at the moment, there's no Core32 version of MB64(e) and only an alpha version of MBLC. And a MBLC is all about motorfaders, I guess it doesn't support using encoders instead of them, and you would need LED rings on the encoders if that box should make any sense. So if you really want to use a Core32 you'll either have to do a massive bit of programming yourself or wait for TK to release a mb64(e) version.

On the other hand, the only real advantage I see in using a Core32 for a simple Midi controller is the onboard USB. You could use a Core8 MB64e with built in GM5 Midi interface just as well, and even grab the 5V from the GM5.

regarding current consumption - I guess one DIN module will need about 20 mA, mainly used by the pullup resistors. current for the DOUT modules depends mostly on the current the LEDs you're using needs. bright LEDs will use up to 20 mA PER LED, so for a bus powered box I'd suggest to either skip the LEDs altogether or use not too many low power LEDs with suitable resistor values on the DOUT. The Core (8 or 32) itself doesn't need much current, I guess in the range of 50 mA (never measured it). The most problematic consumers are LCD displays with LED backlight. There's a huge range of current consumption between different models. It can go as low as 80 mA, but there are also models that take 300-400 mA when adjusted to good brightness.

Given these estimated values, the total current depends mostly on what exactly you want to build. A box with only a few encoders, no LCD or LEDs can go as low as 100 mA or less. If you want a huge and brightly illuminated flashing monster, better forget the bus power idea ;-)

S

[lylehaze]

Another thing to be aware of: at the moment, there's no Core32 version of MB64(e) and only an alpha version of MBLC. And a MBLC is all about motorfaders, I guess it doesn't support using encoders instead of them, and you would need LED rings on the encoders if that box should make any sense. So if you really want to use a Core32 you'll either have to do a massive bit of programming yourself or wait for TK to release a mb64(e) version.

On the other hand, the only real advantage I see in using a Core32 for a simple Midi controller is the onboard USB. You could use a Core8 MB64e with built in GM5 Midi interface just as well, and even grab the 5V from the GM5.

regarding current consumption - I guess one DIN module will need about 20 mA, mainly used by the pullup resistors. current for the DOUT modules depends mostly on the current the LEDs you're using needs. bright LEDs will use up to 20 mA PER LED, so for a bus powered box I'd suggest to either skip the LEDs altogether or use not too many low power LEDs with suitable resistor values on the DOUT. The Core (8 or 32) itself doesn't need much current, I guess in the range of 50 mA (never measured it). The most problematic consumers are LCD displays with LED backlight. There's a huge range of current consumption between different models. It can go as low as 80 mA, but there are also models that take 300-400 mA when adjusted to good brightness.

Given these estimated values, the total current depends mostly on what exactly you want to build. A box with only a few encoders, no LCD or LEDs can go as low as 100 mA or less. If you want a huge and brightly illuminated flashing monster, better forget the bus power idea ;-)

S

I'm picturing a "special" USB hub with a gasoline generator to power the attached peripherals.. :drool:

available in pull start or kickstart versions.

LyleHaze

[findbuddha]

The USB page on wikipedia mentions a Battery Charging Specification whereby devices can get up to 1.8A - presumably only possible on those standalone USB chargers for mp3 players.

I suppose I'll just build something and measure the power draw to see if I can bus power it :)