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.


--
JF