Viewmaster wrote:I tried connecting the 3v laser to the USB supply with a series resistor but no success so far.
There is a limit of 100mA on a USB port so if your laser uses more than that the port shuts down. If it's an active USB device during initial handshaking it can request up to 500mA should it need it. But I would be surprised if a laser diode needed anything like that much. If the PC is a laptop the limits could be lower, but they shouldn't be. Try an ordinary (visible) LED at 10mA first. Yer average red LED in series with 330R should do it.
Steve A.