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

[Robert Hildebrand]

Hi Douglas,

the data sheet of the LM1086 suggests a diode as a protection when shorting
the input. The rectifier bridge of the ethernut avoids this situation. I am
suppling an ethernet using an USB interface for some months. It is not an
official design but works quite well. The regular power input is left open.

Buffering the 5V using a large capacitor is not the only solution. Another
approach could be to provide a switched regulator on your extension board
and using a high input voltage (e.g. 24V) and a large input capacitor
together with a diode or recitifier bridge. Discharging the input capacitor
is no problem until reaching the minimum input voltage of the regulator,
supervising of the input voltage could be done by a comparator (internal or
external), which can be polled in the idle task or interrupt.

Combining the MMC card with a self programm feature sounds good and leeds to
the question of developing a bootloader for the ethernut, wich stays in the
flash. This could be part of Nut/OS or independent. At the moment I am
working with at a Mega128 projekt where I switch between application and
bootloader using special commands. If the application hangs there is a
"reset while button pressed" fallback solution. I use USB for communication
and get really fast programm times.
This application runs without Nut/OS (sorry Harald) but used Ethernut as a
evaluation plattform before the hardware was ready. I still keep this
bootloader for downloading Nut/OS application to the Ethernut.

Robert

--
Dipl.-Ing. Robert Hildebrand

Fraunhofer-IMS
Abteilung System- und Anwendungstechnik
Finkenstr. 61
47057 Duisburg

Tel.: +49 203 / 3783 - 237
Fax:  +49 203 / 3783 - 277


Email: robert.hildebrand at ims.fhg.de


-----Ursprüngliche Nachricht-----
Von: en-nut-discussion-bounces at egnite.de
[mailto:en-nut-discussion-bounces at egnite.de]Im Auftrag von Douglas
Pearless
Gesendet: Mittwoch, 20. Oktober 2004 22:06
An: 'Ethernut User Chat (English)'
Betreff: [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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