Shop OBEX P1 Docs P2 Docs Learn Events
Save variables on power down — Parallax Forums

Save variables on power down

ArchiverArchiver Posts: 46,084
edited 2002-10-23 08:35 in General Discussion
I'd like to make use of the ability to write to non-volitile memory on
powering down my BS2SX project. Can anyone point to circuit examples that
can set a pin to indicate impending shutdown as well as short term power
supply (capacitor?) while the write happens?

I'm using the Stamp and a BOB-II as part of a remote control for a 35mm SLR
and would like to keep track of the number of photos taken. Then on
power-down the count is saved and read back in on power-up.

-Eric

Comments

  • ArchiverArchiver Posts: 46,084
    edited 2002-10-23 05:31
    I've never tried this, but -- in theory -- you should be able to do this
    by using a super capacitor or even a battery to hold power to the Stamp.
    Then you'd just read the "main" power and if you see it go to zero, save
    your data and either go to sleep or wait for sleep to overtake you :-)

    The BS2SX takes quite a bit of power, though, so I'd say you wouldn't
    have much time unless you use a battery (and then charge the battery
    while power is good).

    Al Williams
    AWC
    * Floating point A/D
    http://www.al-williams.com/awce/pak9.htm



    >
    Original Message
    > From: Eric Dustrude [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=ws1FaU2gtW4xKK8gXnFUiOcI4NvoFQE0XGR1LDbvOjnxBcJv__r9TPy1e6Lobk-MaxtksopCHxiSsPn3hw]models@d...[/url
    > Sent: Tuesday, October 22, 2002 11:21 PM
    > To: basicstamps@yahoogroups.com
    > Subject: [noparse][[/noparse]basicstamps] Save variables on power down
    >
    >
    > I'd like to make use of the ability to write to non-volitile
    > memory on powering down my BS2SX project. Can anyone point to
    > circuit examples that can set a pin to indicate impending
    > shutdown as well as short term power supply (capacitor?)
    > while the write happens?
    >
    > I'm using the Stamp and a BOB-II as part of a remote control
    > for a 35mm SLR and would like to keep track of the number of
    > photos taken. Then on power-down the count is saved and read
    > back in on power-up.
    >
    > -Eric
    >
    >
    >
    > To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    > from the same email address that you subscribed. Text in the
    > Subject and Body of the message will be ignored.
    >
    >
    > Your use of Yahoo! Groups is subject to
    > http://docs.yahoo.com/info/terms/
    >
    >
    >
  • ArchiverArchiver Posts: 46,084
    edited 2002-10-23 05:40
    If the only thing you're saving is the photo count, I would suggest that you
    simply save the count each time it gets incremented. You might want to hang
    a supercap on the downstream side of the regulator, just to get you through
    the write-cycle in case power drops when you're trying to save your photo
    count.

    -- Jon Williams
    -- Parallax

    In a message dated 10/22/02 11:21:21 PM Central Daylight Time,
    models@d... writes:


    > I'd like to make use of the ability to write to non-volitile memory on
    > powering down my BS2SX project. Can anyone point to circuit examples that
    > can set a pin to indicate impending shutdown as well as short term power
    > supply (capacitor?) while the write happens?
    >
    > I'm using the Stamp and a BOB-II as part of a remote control for a 35mm SLR
    > and would like to keep track of the number of photos taken. Then on
    >




    [noparse][[/noparse]Non-text portions of this message have been removed]
  • ArchiverArchiver Posts: 46,084
    edited 2002-10-23 06:38
    I'm pretty new to this game and thought I'd read somewhere that the
    performance penalty for writing to EEPROM might be large (relative to
    RAM). As I'm attempting to juggle a number of inputs besides the
    photo count and want a good response time for all the inputs, I
    thought the writing to EEPROM might be a bottleneck. I also see from
    a little more reading that the time to write may not be as
    significant as I thought - relative to the execution speed of the
    stamp anyway.

    I guess I should experiment with it before making the problem more
    complcated than it needs to be [noparse]:)[/noparse]

    Thanks for your quick response!

    -Eric

    --- In basicstamps@y..., jonwms@a... wrote:
    > If the only thing you're saving is the photo count, I would suggest
    that you
    > simply save the count each time it gets incremented. You might
    want to hang
    > a supercap on the downstream side of the regulator, just to get you
    through
    > the write-cycle in case power drops when you're trying to save your
    photo
    > count.
    >
    > -- Jon Williams
    > -- Parallax
  • ArchiverArchiver Posts: 46,084
    edited 2002-10-23 08:35
    I'll have to check with our engineering staff, but I believe that the EEPROM
    write cycle is 10 to 25 milliseconds -- which is certainly faster than
    winding to the next frame of film.

    -- Jon Williams
    -- Parallax

    In a message dated 10/23/02 12:38:26 AM Central Daylight Time,
    models@d... writes:


    > I'm pretty new to this game and thought I'd read somewhere that the
    > performance penalty for writing to EEPROM might be large (relative to
    > RAM). As I'm attempting to juggle a number of inputs besides the
    > photo count and want a good response time for all the inputs, I
    > thought the writing to EEPROM might be a bottleneck. I also see from
    > a little more reading that the time to write may not be as
    > significant as I thought - relative to the execution speed of the
    > stamp anyway.
    >
    > I guess I should experiment with it before making the problem more
    > complcated than it needs to be [noparse]:)[/noparse]
    >
    > Thanks for your quick response!
    >
    > -Eric
    >




    [noparse][[/noparse]Non-text portions of this message have been removed]
Sign In or Register to comment.