[En-Nut-Discussion] Mass storage and real-time clock daughter boardfor the Ethernut-2.

[Alexander Baranov]

If we assume that current consumption would be about 0.5 A, the time
constant with 1F capacitor  is equal to 10. Then, according to formula U =
U0*exp(-t/theta)  we come to conclusion that the capacitor will be
discharged to 85% of initial voltage during 1.6 seconds.
If I am wrong, let senior comrades correct me. But I propose also to look at
the specs of that ionistor and to the value of it's own resistance.
Regards, Alexander.


----- Original Message ----- 
From: "Douglas Pearless" <Douglas.Pearless at pearless.co.nz>
To: "'Ethernut User Chat (English)'" <en-nut-discussion at egnite.de>
Sent: Wednesday, October 20, 2004 4:06 PM
Subject: [En-Nut-Discussion] Mass storage and real-time clock daughter
boardfor the Ethernut-2.


> Greetings people,
>
> For a while I have had a MMC card attached to my Ethernut, with a crude
FAT
> file system.
>
> Then in working with Michael Fisher, he modified his FAT on IDE/SD Card
code
> to also work on the MMC card (Thanks Michael!!) so we didn't end up with
> lots of code doing similar things and I killed off my code.
>
> Now, if anyone is interested, I will soon (about a month) have a low cost
> daughter board design completed that adds up to 8MB-1GB non volatile
storage
> in the form of a industry standard MMC card, a battery backed up real-time
> clock that detects power failure and notifies the CPU, and re-routes the
> RS-485 interface to the same end of the board as all of the other external
> connectors on the Ethernut-2 so you can put your project into an enclosure
> with all of the connectors at one end.
>
> I'd like some comments:
>
> (1) Is this of interest and should therefore be published?
>
> (2) I am considering using a particular Maxim RTC chip that allows me to
> have a battery (or perhaps a 1 Farad capacitor) of such a size that the
> Ethernut-2 could operate long enough to flush all of the FAT buffers to
the
> MMC and close files etc, and maybe send out an alert.
>
> (3) How much current would a 1 Farad capacitor supply at 5v, and for how
> long?
>
> (4) Does the LM1086 have reverse voltage protection so that if my daughter
> board is supplying power to the 5v line (and hence the 3.3v line) with no
> input power to the LM1086, will this damage the LM1086.
>
> (5) I may also add a reset button that can be accessed from the same side
as
> all the connectors are on so that the unit can be reset without having to
> pull the power from the unit (when it is in an enclosure).
>
> (6) In a later revision I was thinking of allowing the Ethernut to Boot
and
> self program from the MMC card, meaning that customers could be sent a new
> MMC card (e.g. a cheap 8MB one) that reprograms their Ethernut without
> requiring an engineer or on site visit, a good idea?
>
> Douglas.
>
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