Author Topic: µCurrent - Where am I going wrong?  (Read 2183 times)

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Offline rocksoftTopic starter

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µCurrent - Where am I going wrong?
« on: September 05, 2012, 08:39:15 pm »
Hi,

Got my µCurrent the other day, bought it specifically because I have a 3.0v microcontroller system and I need to measure the sleep current accurately, it draws somewhere in the region of 900na.

When I connected it all up it works fine for the milli-amp and micro-amp range and the micro runs and I get the output I expect from the µCurrent. However, when I switch to the nano-amp range it doesn't work as I was hoping. My micro fails to run and the voltage drop I get from the µCurrent is about 50% from my 3.0v source.

Since this is a micro it has some distinct levels of current consumption, at bootup it's around 6 milli-amps, it then does some work which takes around 20ma it then goes to sleep which is the current I wish to measure.

I'm suspecting the µCurrent is not allowing it to boot properly as I'm probably exceeding some of the spec for the range I'm selecting when the micro boots up.

I really just wanted to ask if anyone had any advice or point me to where I might be going wrong. I'm thinking I need to bypass the µCurrent initially while the micro boots up and goes to sleep, is it "safe" to just bridge the "current+" and "current-" terminals? By safe I mean will it damage the µCurrent?

Cheers,

Liam.



 

Offline gxti

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Re: µCurrent - Where am I going wrong?
« Reply #1 on: September 05, 2012, 08:44:16 pm »
You can always short the current terminals. There is nothing in the uCurrent that would try to drive current in or out of the terminals, so shorting them together just forces it to a zero reading.
 

Offline EEVblog

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Re: µCurrent - Where am I going wrong?
« Reply #2 on: September 05, 2012, 09:39:02 pm »
With hindsight, a small shorting switch across the input would have been handy I think.
Easy to mod in such a switch though.

Dave.
 

Offline krish2487

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Re: µCurrent - Where am I going wrong?
« Reply #3 on: September 06, 2012, 03:46:13 am »
@liam

I think your problem is with the burden voltage drop on the current shunt. There is nothing wrong with your ucurrent, nor are you doig anything wrong.

the 50% drop on the shunt in the nano amp range is indicating that the current consumption is more than what you expect the micro to draw.


Try to see if it works when you switch the range "on the fly" to nano amps after you apply the power in milli/micro amps for a couple of tens of seconds.

If your guess is right about the initial current consumption, let it boot up, settle down and then change the mode to nano amps range.
If it works, you know you are right.. If it doesnt, then you know your estimation of the current drawn is off..
If god made us in his image,
and we are this stupid
then....
 


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