[time-nuts] Motorola Oncore UT+ firmware upgrade & backup power questions

Attila Kinali attila at kinali.ch
Sun Mar 15 18:40:23 EDT 2015

On Sun, 15 Mar 2015 11:05:53 -0400
paul swed <paulswedb at gmail.com> wrote:

> I agree with Atilla from what I have seen. Its actually somewhat difficult
> to measure this level of current.

It's not that difficult. You just need a good DMM. Standard ones
will not work as they have resolution limits in the range of 10-100uA.
A semi-decent Fluke handheld gets you already to 0.5uA. If you get
a reall DMM, then you will start worrying about the surface currents
on your device (FR4 has a quite low surface resistance of 10-100Mohm,
depending on humidity and whether you have any finger prints on it)
and anything you have in your setup (finger prints, small residues
of oily stuff, dirt,...)

The bigger problem is, that you have to make sure you have no floating
inputs anywhere (inputs are not clearly 0 or 1, will have more input leakage
current, additionally to the "shot trough" they cause inside the chip).
If you use diodes for decoupling parts of circuitry, you need those with
extremely low reverse current (in the low nA) and those will have high
forward voltages (>1V, the ones we used had iirc 2V). etc pp
Ultra low power electronics is probably as messy a field as ultra low
noise electronics.

> But all is not lost. Even if the unit is
> drawing 1-10ua because something is going wrong. Simply add a battery
> holder and 2 X AAA or AA or ...

Please be aware that AA and AAA cells have a much higher self discharge
than coin cells. A CR2032 is usually of LiMnO2 chemistry, while AA/AAA's
are usually ZnMnO2. Also coin cells are optimized for long life times,
with very little current drawn, while most AA/AAA are not, or not as much.
Ie, i wouldn't expect an AAA cell, and much less an AA cell to last 10 years.

			Attila Kinali

< _av500_> phd is easy
< _av500_> getting dsl is hard

More information about the time-nuts mailing list