XPost: sci.electronics.design
From: speffSNIP@interlogDOTyou.knowwhat
On Fri, 07 Dec 2007 03:33:33 GMT, "West" wrote:
>Using a 555 or similar type chip, I would like to have the output change
>from low to high or high to low every time the system is turned on. IOW, the
>output is a high, then the system is turned off. When the system is turned
>back on, the output goes low. Each power up of the circuit changes or
>"flips" the output state. I am willing to incorporate CMOS and a battery
>back up in the design. Some of the ideas I entertained is a divide by 2 in
>front of the toggle, giving me the same state every other time. However, I'm
>not sure how to do this practically or if it's the way to go. Any
>suggestions out there? All comments welcomed and thanks.
>
>west
You can buy relays that do this (alternating relays), which are used
for load levelling on machinery (among other things). They are big,
use a lot of power, and cost a fair bit of money, and have a limited
life.
If you want to do it at a chip level, the microcontroller suggestion
is a good one, parts cost will be minimal, and only a few parts
required (an external reset circuit may be called for). Lifetime is
somewhat limited, still *far* better than a relay, and can be improved
by additional orders of magnitude by clever programming to load level
erase operations on EEPROM cells. Not difficult to do. The same thing
could be implemented with a battery-backed CMOS FF (eg. 4013), with
more parts. In either case you'd have to reliably detect and debounce
power state changes. Some of that can be done in firmware with a
micro.
Best regards,
Spehro Pefhany
--
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speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
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