15C LE spike fix

[jebem]

(05-01-2014 12:13 PM)Jeff O. Wrote:  However, in looking at Lyuka's plot of current consumption in program run operation (reproduced below), I think I stand by my assertion that a capacitor won't do much to prevent voltage drop during program execution. There is a tiny AC component, but it is mostly DC which must come from the battery. I don't think that a capacitor will have any impact on that. The capacitor does seem to tame the current spikes in other situations.

That graphs shows just one part of the story. You are looking to the average current there, not the transient current pulses. That pulses can have several hundred of mA during just 1uS. To measure that current pulses we need to use a scope measuring the voltage at the Vcc processor terminals as well.

What are being proposed by others, like Lyuka, is to add additional capacitance (up to 100uF) to the existing 10uF decoupling capacitor, to improve the battery efficiency.

But of course one can not extract more energy than the one existing available in the cell battery! That is one limiting factor...
What we are discussing here is how that energy is delivered. Cells can only deliver low amounts of current in a kind of steady way (due to its high internal impedance) and so they are unable to supply instantaneous large amount of current. Capacitors can. That is why we couple a cap with a battery.

In the end, if the 15C LE has some feature missing in the design, like telling to replace the battery when it is low, nothing we can do with a capacitor will fix them. I agree with you.