Measure the current drawn by my ardino mini?

Hello!

Everyone on this forum has been so helpful helping me get my project together, so i thought i’d ask a rather noobish question in the hope that someone can shake their head sadly and tell me the probably obvious answer.

I’m running a 5v arduino pro mini from a USB connection and would love to see the current it draws in sleep mode. How/ where should i attach my multimeter? I don’t want to hurt my arduino! Should i connect a resistor somewhere of a known resistance and read the voltage across it instead?

Huge thanks!

-Susan

Either way, you're going to have to place something in series with the load (to measure the voltage drop across a resistor you'd still have to place the resistor in series with the voltage line, and you'd want to use a small resistor 1ish ohm's or so, so your power supply voltage doesn't drop too much).

I'm assuming you're using either an FTDI cable or an FTDI basic breakout (from SparkFun) or something, right? (The Pro Mini has no USB on it - just ports for the +5V, gnd, TX and RX).

It will probably be best to use a breadboard, and (solid) wires.. Insert wires into the FTDI cable / breakout, and drop those into spots on the breadboard. Then use more wires to bring the connections back to the Pro Mini.

Then you're free to easily place your multimeter in series on the +5V line and measure away! (Remember most multimeters have different plugs for measuring current and voltage!)

Something like:

USB breakout -> breadboard -> multimeter -> breadboard -> Arduino

Does that make sense?

I assume a 'sleeping' AVR draws some microamps of current. Be sure to check the specs and range capacity of your multimeter to see that it is up to the task to measure such low current.

Lefty

thank you so much for such a clear answer! I’ll be sure to check my multimeter. Yes, it’s on a breakout board, so i’ll do as suggested :smiley:

Great! it dropped from 11.3mA to 0.59 mA in sleep mode.

Just to say the 0.59mA in sleep mode is quite high. There are other processors that will sleep at a tenth or less of this current, if this is a big issue.

for the moment i think that's ok, it can sleep for 379 hours with my back of the envelope calculation! am i right in saying that the capacity of the battery stays the same if you put more then one battery of the same capacity in series? so one capacity=220mAh battery has the same capacity as two of them stacked?

Yes if the batteries are in series then the current capacity is the same but the voltage is doubled.

Never put two batteries in parallel without circuitry to prevent one battery charging the other.