A lot of makers don't know how important it is to know the current draw of your project, or why you need to know this. In this tutorial I will explain to you how to measure the current draw of your project, and why it is so important to know this. This is a abbreviated tutorial, for the complete tutorial click on this link

Step 1: Items You Need for This Tutorial

Wall 5v 1A power adapter
DC Barrel Jack Adapter - Female 5.5x2.1mm
Multimeter with removable probes and dedicated Amp measuring port
Banana to Alligator clips multimeter probes
Adruino Uno R3
4 jumper wires

Step 2: Connecting the Probes to the Arduino UNo

NOTE:Do not connect the power adapter until everything is connected properly.

Connect 2 jumper wires to the screw terminals of the barrel adapter as seen in the picture above. Use a red lead for the + terminal and black for the - terminal.
Connect the black jumper wire (- or gnd terminal) from the barrel adapter to gnd port on your Arduino Uno
Connect the red wire (+ or 5V power) to the red alligator clip attached to the multimeter probe
Connect another jumper wire to the black alligator clip attached to the black mulitmeter probe. Connect the other side of the jumper wire to Vin on your Arduino Uno.

Step 3: Connecting Probes to the Multimeter

Connect the black banana clip connector to the port labeled COM (Common Ground) on your multimeter
Connect the red banana clip connector to the port labeled A (Amp) on your multi meter. Even though the Arduino UNO is only going to draw 30 to 35 mA it is always a good idea to connect it to the A port instead to the mA port to protect your multimeter from being damaged (See my blog for full explenation
Put the multimeter dial to A dc (direct current)

You are now ready for measuring the current draw of your project

Step 4: In Series, or Inline With Your Power Supply

We have now put your multimeter in Series or sometimes called Inline with your power supply. The current travels through the red probe lead to your multimeter, and passes through your multimeter out of your black probe lead to your Arduino Uno (see picture above)

If you connect your power adapter to the barrel adapter your Arduino will power up, and the display on your multimeter should read 0.032 Amp or something close to that. This translates to 32mA (a mA milliAmp is a 1000nd of a Amp).

Your multimeter might look a bit different then mine and might need more configuration that is specific to your device. Read the instructions that come with your multimeter to configure it properly.

Monitor your project current consumption for a while to see what the max current required for your project. If your project would draw more then a Amp you need to make sure your power adapter is able to supply the current requirements of your project (1A or higher).

Now you can also prevent spending to much on a power supply by buying a power supply that can handle your project, and not spend money on a 3A power supply when you only need 1A.

Go to my blog where you can find a bid more info by clicking on this link.