Sufficient power supply

Hi all, I've been struggling with some power issues with my Arduino project.

I have Arduino Uno, RFID card reader and LCD display (with backlight)

Originally I had only Arduino and RFID. Everything worked as long as I had it connected via USB. Then I tried power adapter 5V, 2I. The arduino and RFID worked (ON diodes were HIGH), but the RFID antena's diode didn't blink when scan.

So I tested U and I at the RFID VCC and GND pins and I got 3,5V and 1,5I.

I thought "nevermind"..., I will work with the USB for the moment. Then I connected LCD display. It works if connected alone, but when I tried to plug it all together, RFID's ON diode didn't even blink.

And finally to my question:

What power supply (U,I) would you recommend for this case?

Best regards, Watchick

The current is in Ampere: http://en.wikipedia.org/wiki/Ampere So your adapter is 5 Volt and 2 Ampere ?

The Arduino Uno power socket is for 7 ... 12 Volts. Can you get an adapter of 7 ... 12V ? An adapter of 500mA or 1A should be enough. I use a 9V adapter for my Uno.

You can use an adapter of 5V, but you have to connect that to the +5V pin of the Arduino. That way you bypass the voltage regulator on the Arduino Uno board.

I use those “Plug-in” Breadboard power supplies for my projects and with the addition of a few (3 or 4) .1uF caps 'Sprinkled about the Bread Board power rails AND a 10uF and a 470uF cap at about the middle of the physical length of the supply rails for general 5V distribution (same for 3V3), If I have a heavy load (> 200 mA) that load gets powered separately… With the same Electrolytic’s. I leave the VR on the Arduino board to Only supply power to the Arduino. I am a little more aggressive about by-passing because I use the “Extension cable, shield and bread-board header” designed by Liudr you can see it on Inmojo or Dipmicro But the components are never ‘un-necessary’ even in real life… When I transfer those parts to a circuit board whether a “Home Made” or professionally made or just hand wired… I Know it will work. 1 .1uF cap per IC the 470 uF for low frequency or specifically battery operated w/o a regulator and the 10 uF cap for the rest… usually I use several 10 to 22 uF caps distributed about the board and the big caps where the power enters the PCB or where the regulator is and I Always use a 100 uF cap on the input to the regulator. Might sound either paranoid or wasteful… But the parts are inexpensive insurance… A Hard learned lesson from 30+ years of circuit design.
It’s a Bi**H when you call the chief engineer over for help and all he says is "Do You Have Enough By-Passing and you say yes I think so and he plugs in a 22uF cap and the problem goes away. Very Embarrassing and only done once or twice. Experience is my guide.

Doc