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

paul swed paulswedb at gmail.com
Sun Mar 15 22:23:41 EDT 2015


Atilla
Nor do I expect them to last 10 years, more like 1-2 years if the units
drawing the currents mentioned. Being external they are easy to change and
measure. Also cheap.
Only do this on boards that can't be replaced etc.
Regards
Paul

On Sun, Mar 15, 2015 at 6:40 PM, Attila Kinali <attila at kinali.ch> wrote:

> 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
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