USB power Windows/Mac

[jerash]

Hello,
this afternoon, i've experiencing for two hours over the following problem :

When hitting hard a cymbal (DIY), the MD would not respond for about 1 second, so missing some hits on snare/kick/hihat. Then it come back to normal.
Sometimes, hitting too hard would cause the MD to hang, needing a restart.
Sometimes, it is like messages where in hold for one second, and then sent all at the same time after that second.

So, i tried many times to change the resistors values, because I thought my pads where too "hot", sending a too strong signal to the megadrum, because everything was fine when hitting the cymbals softly.
But it didn't change anything, neither by changing to a smaller piezzo less sensible.

The solution came from another post (http://www.megadrum.info/forums/viewtopic.php?f=4&t=1927&p=21055&hilit=usb+hub+external#p21055) talking about using an external powered usb hub to power the MD.

I don't have such a device, so i switched from my MacBook Pro to an old Windows laptop, and guess what.... the problem disappeared immediately !

So here is my conclusion : i think that the USB device declaration is not handled correctly by the macintosh so it doesn't give enough power to the MD.
What the cause could be ? either from the OSX Lion usb driver handling, or in the MD PIC firmware being not fully class compliant, or not 100% compatible with the brand new OSX Lion ?

Any suggestion is welcome as i would really appreciate to avoid using an external hub.
thanks, Raphaël

[dmitri]

The USB power is not controlled by OS/drivers, it is all in hardware. A USB port on a PC/laptop MUST provide +5V at 500mA.
I have a MacBook Pro 17" running Mac OS X Lion and I have no problems whatsoever using MegaDrum with it. In fact, before sending the kit to you it was tested on this very laptop.
I've also tested MegaDrum with MacBook Air 11" and had no problems either, including configuring it using MegaDrum Manager.

[jerash]

ah....my macbook is a 15''
I'll test again tomorrow with the two computer, maybe trying different usb ports...

off topic : for my job i had programmed some usb functions in C under windows, to verify power requirements of usb hard disk drives. Windows offers options to set the usb port with a limitation to 100mA. These elements are part of the usb descriptor. Maybe not applicable to audio peripherals.

[dmitri]

Power requirements in a USB device descriptor is for an OS to complain when a USB device power declaration exceeds OS's expectations. OS cannot limit current but a PC (hardware) may shut off a USB port when it senses too much current is being drawn (short circuit protection).

[jerash]

ok I trust your software knowledge

Further experiment today : Plugged on the mac again, everything goes fine So i don't really understand what's happening, maybe i have some soldering inside not that good. I'll check with time.

My only suggestion would be that i was using a hall effect sensor by honeywell for the hihat, but the data sheet says only 7mA of current under 5VDC. But today i switched to a regular on/off switch too, and until everything goes fine i'm happy because we'll use the unit in live show and i need something working 100%.

thanks.