On Tue, 11 Sep 2007 19:06:23 -0500, flipper wrote:

On Tue, 11 Sep 2007 14:41:16 GMT, "Bill" wrote:

"John Fields" wrote in message
. ..
On Tue, 11 Sep 2007 08:31:49 -0500, John Fields
wrote:

On Mon, 10 Sep 2007 02:30:56 GMT, "Bill" wrote:

Anyone know of a way to reverse polarity (9 to 12V DC) each time the
power
is removed? In this gadget I have there is a small 12V supply. When I
turn
the gadget off and then turn it back on, I wish to have the 12V reverse
polarities. For another example, I have a black box with 2 posts, the
top
post is +12v and the bottom post is 0v. I turn the power off and the
next
time I turn the power on, I would like the top post to be 0v & the
bottom
post to be +12v. Is there like a simple flip flop chip or ?? than can
accomplish this task? All comments most appreciated. Thanks in advance.

---
Please crosspost instead of multi-posting.

I've crossposted this to seb and sed.

You could use a 555 pulsing on power-up to toggle a DPDT dual-coil
magnetic latching relay by using one set of the relay's contacts to
steer the pulse and the other to switch a DPDT single-side-stable
relay on and off to get your polarity reversal. The caveat is that
the pulse to the latching relay has to be short enough so that it'll
be gone before the armature gets to the other contact or both relays
will buzz or, at least, switch back.

You could also use a 555 to drive a solenoid which would toggle a
DPDT alternate-action pushbutton switch.


John ... This is all low current operations. How about something like a
divide by 2 triggering a 555? Can this give alternate highs and lows on pin
3, the output? I can figure what to do after pin 3. I also wonder if I'm
explaining the problem adequately.

Your description is murky and incomplete with the biggie being just
what you mean by turning what on and off..

There has to be a retained 'memory' of what the previous state was so
if one assumes you mean that all power is removed from 'everything'
then the 'memory' device must retain it's 'memory' without power. So
you get suggestions like a magnetic latching relay.

If the power supply itself can remain on, disconnecting the 'red and
black posts' for 'off', or if there can be 'standby power', like what
keeps your PC clock alive when the PC is 'off', then a whole world of
powered solid state devices opens up.

But none of your NE555 and flip flop ideas are going to work if all
power is removed because then there's nothing to 'remember' the
previous state. They go 'brain dead' with no power and will power back
up the same way each time.


Bill
--
JF


A small microcontroller with EEPROM or similar would be a simple solution,
but only if the OP has some experience with them.

Jim