How to check a GSM shield power consumption?

I am trying to calculate the average power consumption of my Arduino Uno connected to a GSM Shield and 4 Led matrices.

When connecting it to a multimeter, like in the attached picture (taken from the Web) and setting the multimeter scale to 200ma, the board runs, but the modem of the GSM shield stops working. When setting the scale to 20, the board is not even powered.

It looks like the multimeter absorbs some power, so the shield has no sufficient power to work?
That’s kind of odd, because I am powering the board with a 12V drill battery stepped-down to 5V (without the multimeter it runs perfectly).

What am I doing wrong? :fearful:

Thank you

instead of a picture from the web, you should post a picture of what you've actually done ;)

  • there is no reason for it to stop working if it is connected through the multimeter (at 200mA), even if there is more than 200mA (and yes, it will draw more than that from time to time) , the multimeter will display "OL" , but everything should work as if it was not there ....maybe your wiring doesn't allow a good contact ?

  • when you try at 2A, do you put the multimeter wire at the right place (20A hole) ?

GSM units like lots of current to transmit, assume amps rather than milliamps.

However this is only during packet transmission, which with most GSM units is for 1/8th of the time (a single timeslot). Thus if it takes 2A (say) to transmit the average current shown on a multimeter would be about 300mA.

Your multimeter on a 200mA current scale will have about 1 ohm of shunt resistance, which at 2A will drop 2V and prevent the GSM unit from transmitting.

So use the 10A scale only for measuring current drain for a high current load like this.

People often get into difficulty powering GSM shields not realising the high peak current requirements. Normally a GSM unit is powered from a LiPo battery in a phone which has no problem at all with sourcing lots of amps.

Thank you for the answer.

As you can see, I connected the multimeter to the breadboard with a pin and am using the 20A scale.
Always with no success… :confused:

hum.... no, I can't see anything useful on these photos ;)

you could try to put the multimeter before the regulator, on the + side of the battery

Thank you alnath. Now it works.