V-USB on a battery powered device

[Ugly!]

Hi. My project is based on a attiny2313 and a ds1302. It's basically a rellay that opens at specifics times of the day. I'd like to set these times via USB and a PC. The device is battery powered with 2 AA batteries (3V). I don't wan't to powered the device via USB.

I´m not sure how should I interface with the USB port in terms of hardware.

- Can I leave the USB Vcc simple hainging?
- Do I have to wire the USB GND with my device GND?
- Do I have to use 3.6V zenner diodes if I'm powering with the 2x AA batteries?
- Do I have to set the USB_CFG_IS_SELF_POWERED to 1 in the usbconfig-prototype.h

Thanks in advance and best regards.
Mat

[Guest]

- Can I leave the USB Vcc simple hainging?

Yes, in fact, you should

- Do I have to wire the USB GND with my device GND?

Yes

- Do I have to use 3.6V zenner diodes if I'm powering with the 2x AA batteries?

I don't think you do, but I hope 2x AA batteries work, test it out first

- Do I have to set the USB_CFG_IS_SELF_POWERED to 1 in the usbconfig-prototype.h

You should
Also remember to rename the file "usbconfig.h", not "usbconfig-prototype.h"

[Mike J.]

- Do I have to use 3.6V zenner diodes if I'm powering with the 2x AA batteries?

In this case you don't need Z-Diodes, the Voltage is lower than 3.3V.