uCurrent Gold meter - basics

[electronicsfun]

I'm still a newbie at electronics, and I could use some clarification on how to not overload this device.

From the PDF for the uCurrent, it saids not to put more current than the range for that current selection, or else you might blow the shunt resistor.  This is the top end for each range selection.

    300mA [mA range]
    1mA [uA range]
    1uA [nA range]

Let's say I have a microcontroller that sleeps for 10 seconds, wakes up and lights up LED, and then sleeps for another 10 seconds. I want to measure sleep current. I would keep the selector switch in [uA range] to measure the sleep current consumption. But when the microcontroller wakes up, the wake up activity consumes more current than the 1mA allowed in the [uA range]. Would that blow the shunt resistor? Would I have to move the selector switch from [uA] to [mA] quickly before the microcontroller wakes up? It seems like a pretty risky operation. Wondering if my understanding of overload current is correct, and if there's a better way of making this measurement?


Also, if you opt to use 3xAAA, would you solder wires from the AAA battery holder directly to the coin cell contacts? Or is there a better way I'm not seeing?

Thank you.
Jason

[michaeliv]

For the exact scenario you're describing it should be fine. The uA resistor is 10Ohms @ 0.125W so it should be good for up to 110mA on the uA range.
Though you will get a rather large voltage drop in your circuit ... so that might reset your micro(unlikely).
Also not sure if you might damage the rest of the uCurrent circuit, though at first glance it doesn't look like you would.

[MLXXXp]

I've done some calculations of maximum safe currents. I'm not aware of anyone disputing them.
https://www.eevblog.com/forum/crowd-funded-projects/current-gold-on-kickstarter/msg375819/#msg375819

Edit:
For maximum current if you keep the uCurrent powered up, or add diodes for input protection, see:
https://www.eevblog.com/forum/crowd-funded-projects/current-gold-on-kickstarter/msg376311/#msg376311

And for my mod that adds the input protection diodes:
https://www.eevblog.com/forum/crowd-funded-projects/current-gold-on-kickstarter/msg448208/#msg448208

[Gyro]

It doesn't have diode clamping as standard? 

Sounds like something to add immediately on delivery.

Edit: I've just searched out the schematic... I'm a bit surprised that it doesn't seem to have any input protection at all, even for the opamp. I'd always assumed it was better than that.

The absolute maximum rating on the Max4239 inputs is Vgnd-0.3V to Vcc+0.3V, I suspect that will be damaged before the resistors.