Problem powering my UNO from external power supply!

HI there everybody! I am using an Arduino Uno and an Adafruit Wave Shield to play sounds from an SD card every time one of 2 photocell sensors detects a change in light. It has 2 LEDs (and a 3rd that flickers when there is sound) which work with the 2 photocells.

Plugged into USB:

both LEDs for sensors light up
LED connected between pin 13 and ground flashes a little bit, then flickers in accordance with the appropriate sound being played
sensors work correctly, triggering sounds

Plugged into a 9V 1000mA AC-to-DC converter:

both LEDs for sensors light up, a bit too bright i think
LED connected between pin 13 and ground flashes a little bit, then glows brightly for about 3 seconds
sensors do not work, no sounds play

hmmm! i thought it was because i needed more amperage from the power supply so I changed from 800mA to 1000mA, but that didn't work. now, to the multimeter:

When I check the 5VDC output pin, it reads 7.55 V, and the 3VDC pin reads 3.28 V. The VIN pin reads 8.23 V !!

Otherwise, when the thing is connected to the computer via USB, the 5V pin reads 4.94 V and the 3V pin reads 3.27 V. The VIN pin reads 4.94 V. And the sensors activate the sounds like they should.

So, can anybody help me? What's going on here? Did I miss-wire something on the Wave Shield? Did I fry my regulator or something?


--The Cosmic Matrix

How have you connected the 9v DC adapter to the Arduino?


Remove all other stuff you connected to the UNO, load blink, power it with ac adapter, measure again 5V and VIN. If 5V is still close to 7.5V, you probably have fried your 5V regulator. There are many ways you could have done it. Replace it if you can.

Plugged into a 9V 1000mA AC-to-DC converter:

If this is a transformer-type wall wart, it is probably unregulated, which means it outputs 9V ONLY when about 1000 mA are being drawn. With no load, it may output as much as 20V. To check, measure the output voltage without anything connected to it. If greater than 12 V, you probably fried the 5V regulator on the Arduino.

HI EVERYBODY! Sorry it took me so long to respond, especially when you were all so helpful!

Anyhow, here's the deal:

I have two adapters. One is a Radio Shack Enercell 9V 800mA unregulated wall-wart, which reads just about +10V w/ no load. The other is a WW-104 9V 1000mA regulated wall-wart, which reads just about +9V w/ no load.

I connect it through the 1/8" jack on the UNO.

When I run BLINK without my Waveshield connected, it seems to work even w/ a wall-wart.
But when I connect the Waveshield and hardware, my program CRASHES when I plug in the wall-wart!

I have to unplug the power plug, toggle the Serial Monitor icon and, with the USB still plugged in, the program will run again.

That's the issue. I can take pictures if ya want.

Any ideas? Sorry about the time warp! This project had to be put on the back burner, as it were. THANKS!!