Electronic – Simple rig to measure current drawn in very short bursts

current measurementmicrocontroller

I have a microcontroller based circuit that sleeps most of the time and works in short bursts of less than 1 milisecond and I don't have access to a digital osciloscope so I could record this. I only have a simple one channel analog scope.

So, how did they do that in old times? Is there a way to set up some external circuitry to measure current that is drawn in short bursts?

What I'm thinking is a small low side resistor with a capacitor in parallel, but I'm not sure…

Best Answer

An indirect way to measure the magnitude of a current pulse would be to power the circuit from a capacitor. During each burst of activity by the processor, the capacitor voltage will drop by a value that's proportional to the charge (current × time) consumed during the burst.

ΔV = ΔQ / C = I × Δt / C

As long as you know what C and Δt are, you can determine the value of I:

I = C × ΔV / Δt

Obviously, the capacitor voltage will also "droop" over time because of internal leakage current and any quiescent current drawn by the load, so be sure to take this into account.