duemilanove, ethernet shield and logging shield

Hi all

This is going to be easy, im new to all this but i think i have the answer just want to check.

I have a duemilanove a logging shield and a ethernet shield.

Im using the examples from the site (with updated libraries) for the mod's done to the shields.

Both shields work on there own but as soon as i plug them both onto the duemilanove only the ethernet shield works.

The SD-card examples error.

Using a multimeter i have found the voltage on the 5v drops from 4.7v to 4.6v when accessing the sdcard with the ethernet shield on.

Im powering the lot via at the moment via usb and using the serial monitor for diagnostics. I think the problem is not enough power.

My question is this, can i power the duemilanove via a 12v psu AND still use the usb to the computer or will this damage the duemilanove/pc?

Thanks in advance

Im using this guide http://www.webweavertech.com/ovidiu/weblog/archives/000477.html

can i power the duemilanove via a 12v psu AND still use the usb to the computer

Yes, the Duemilanove has auto-switching on the power source so you can have them both plugged in at once. There are two operational modes: power supplied via the 2.1mm jack (which feeds through the on-board voltage regulator); and power supplied via the USB connection.

The auto-switching circuit favors the external power connection so if there is >6V available via the 2.1mm jack it will isolate the 5V line on the USB port and use the on-board regulator instead.

USB and the onboard regulator can both supply approximately the same amount of current though, so I don't think that will solve your problem if it really is a lack of power. I suspect the problem may be something else, most likely the boards fighting over SPI.

Jon Freetronics: www.freetronics.com Practical Arduino: www.practicalarduino.com