Your old modem power supply should be ok for external power.
@zoomkatI guess Arduino Duemilanove already have a onboard 7805 Voltage Regulator Chip.
Quote from: zoomkat on Dec 21, 2013, 07:34 amYour old modem power supply should be ok for external power.Did you forget that it's an AC power supply giving out 22V with no load?Even rectifying and smoothing will be very close (if not over) the max input for the Arduino.
Your statement does not make much sense
Have you forgotten that he also measured the same power supply with the DMM set to AC volts and got a reading of around 22V?
The data plate on the power supply is 220vac in and 9vdc out.
In the photo his multimeter is on the appropriate settings and he gets an expected reading for a 9v wallwart. I'll let you ponder the readings when the multimeter is not set appropriately.
Exactly, it applies both ways.
Using an almost identical multimeter as the op is using......