How to Measure Current and Why Should You Do It?

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About: My Name is Ab Kurk, and I help people explore the wonderful world of Arduino micro controllers with tutorial,tips and project ideas

Intro: How to Measure Current and Why Should You Do It?

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.

  1. 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.
  2. Connect the black jumper wire (- or gnd terminal) from the barrel adapter to gnd port on your Arduino Uno
  3. Connect the red wire (+ or 5V power) to the red alligator clip attached to the multimeter probe
  4. 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

  1. Connect the black banana clip connector to the port labeled COM (Common Ground) on your multimeter
  2. 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
  3. 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.

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    5 Discussions

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    2 left thumbs

    8 months ago

    Very nice Instructable. I really like the step-by-step approach and your pics and diagram are great. One thing - the end of Step 3 is


    1. "Put the multimeter dial to A dc (direct current)."
      However, the dial position is not labeled "A dc". It is "A" followed by solid line above a wavy line which I believe means Amps regardless of whether voltage is DC (solid) or AC (wavy).
    1 reply
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    arduinomakerman2 left thumbs

    Reply 8 months ago

    Thanks, I am glad you enjoyed it.

    To answer your question; If you watch the video at the beginning of the tutorial you will get a better explanation why. This multimeter has a function button that you press to switch between AC and DC.

    The reason why I don't go into that is because there are so many different types of multimeters that have different ways to set this. Because of this it is to complicated to cover them all.

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    JohnW51

    8 months ago

    Certainly a lot can be learned from checking current of a circuit sometimes and it is also often essential to know the actual current to insure the components are not being overloaded. For currents beyond the capabilities of your meter, you can put a VERY small resistor in series and measure the voltage across the resistor. Simple Ohm's Law calculation gives the current. In fact, current shunts in the range of 0.1 to 0.001 (or even smaller) are made specifically for this purpose. They are usually extremely accurate--something like +/- 0.01% or better. And not as expensive as one might imagine.