How to measure current in circuit?

hi, I tried to measure current rate in ordinary blink program’s led circuit in arduino, so that I interrupted the circuit in between Led’s Ground pin and resistor from digital pin 7 (which I set as Output pin) I connected my multi meter in series in the circuit ( positive of multi meter to led negative and ground of the multi meter to resitor through ground of arduino) but circuit is not working and also it is not showing any current rating, I have dialed- my multi meter in Amps mode even in micro amps mode it is not working.

Are you sure the LED’s the right way round?

What you’re doing is basically what I did a while back as shown in the attached photo.

Just looked at the image. Apparently it shows 30ma. That's OK and even a tad higher than average LED actually needs.

no, not working, is there any problem in my multimeter, I can measure other readings correctly (voltage, resistance), my multimeter has amps measurement feature also. it is mastech MA830 model. but why? it is not working.

Sounds like your meter has a problem. Does the LED also stop working with your meter in the circuit?

You didn't answer my question about the led being the right way round. Presumably if you reconnect the wire the led comes on?

Have you checked the fuse in the meter?

KenF:
Sounds like your meter has a problem. Does the LED also stop working with your meter in the circuit?

yes, when I connect it in series led not working

Venki:
yes, when I connect it in series led not working

It might be worth opening up your meter. It's quite normal to have fuses in the Amp reading line. It could be blown.

JimboZA:
You didn't answer my question about the led being the right way round. Presumably if you reconnect the wire the led comes on?

yes, I checked led connected in the right way, when I connect it directly it is working. While in series only it is not working.

JimboZA:
Have you checked the fuse in the meter?

I think fuse is ok because I can measure other readings like voltage, resistance all are fine.

Thank you

Venki:
I think fuse is ok because I can measure other readings like voltage, resistance all are fine.

I'm not sure if the fuse in a meter is in the circuit for voltage and resistance measurements. The current through the meter for those readings is nowhere near as high as when the actual current from the circuit under test is all going through the meter.

In other words, I think (not 100% sure) that you can make those other readings even if the fuse has blown.

Voltage and resistance do NOT usually go through the series fuse that is there for current measurement. In practice the current flowing through your meter for those measurements is tiny. So any fuse that is usable for current would be pointless.

Edit: Agh beaten to it by JimboZA :slight_smile:

Yeah!!!!!!!!!!!!!!!! Thank you guys. Fuse only gone. Now it is working.

Excellent.

So now you need to ask yourself, what you did to pop the fuse last time you used the meter.....

yes, before somedays I measured Higher current more than fuse rating. Thank for helped me.

In my meter there is three port one is com and another one is 200 ma max and then 10 ADC port is confusing. It is stands for 10 amps and DC only or 10 AC and Dc like that. and laso it is mentioned 10 A max- unfused. Means if I used more than 10 amps means what will happen meter circuit will blown? And also 10 ADC pin only metioned with amps rating, so Within this amps How much maximum volt I can measure?

OK, the fuse is in the 200 mA circuit in common with the voltage and ohms ranges. As stated in the manual, it is a 200 mA fuse. It is almost impossible to blow the fuse on the voltage and current ranges because the internal resistances of these ranges prevents that much current flowing, though you can burn out other parts of the meter with excessive voltage.

The 10A range consists of a rather sturdy chunk of resistance wire directly between the COM and 10A terminals. It may actually read values well in excess of 10 Amps. Note that power dissipation is proportional to the square of the current, so that it will heat up four times as much if you double the current. Overloading this part (for any significant duration) will cause things to melt, such as the solder connecting that shunt wire and/ or the plastic case of the meter and just as likely, the test wires to the meter (or in fact, their insulation).

Note that inserting the meter in series with logic circuits introduces a substantial resistance and therefore voltage drop into the circuit. The current ranges generally correspond to 200 mV full scale and this drop can easily alter the behaviour of the circuit you are trying to test, so you need to use the 200mA range or even the 10A range for testing current draw.

yeah!!! this is very useful me and make me on sense. Thank you so much...

Paul__B:
Note that inserting the meter in series with logic circuits introduces a substantial resistance and therefore voltage drop into the circuit. The current ranges generally correspond to 200 mV full scale and this drop can easily alter the behaviour of the circuit you are trying to test, so you need to use the 200mA range or even the 10A range for testing current draw.

It sounds like your are very experienced hand. Is there any other gadgets for testing things and analysing, and also measure currents without affect the behavior.

Thank u so much...

Well not that you can measure current with one, but an oscilloscope’s very useful for seeing how voltage varies with time. You can also measure more than one signal’s voltage at the same time, so you can see (for example) the relationship between an output and the input that controls it.

Jimboza... thank you