On Mon, 10 Sep 2007 02:30:56 +0000, 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.

For how much current? Is it permissable to draw some primary current in
the 'off' state? A nineteenth-century solution is a 3-pole 4-position
rotary switch with no stop and a one-way ratchet. Position 0 is off, 1 is
top-post-positive, 2 is off, 3 is bottom-post-positive.

If you can draw some standby current, you could build the equivalent with
two flipflops and a 2 - 4 decoder, with a debounced pushbutton as the
clock. That would actually cost less than a rotary switch, but you will
still need a relay or an H-bridge if you need substantial output current.