best way to reverse polarity on solenoid

Well not really wasted.. I am grateful for what you posted.  It was very helpful.  I have at least on solution now thanks to you!   

I even thought about using a flip flop IC to flip the polarity but then again even they use power of a sort although it might be alot less than other methods.  I think an IC chip uses at least 3 ma @ 5 volts  even when sitting there doing nothing.   

THANKS again.  

Learning is never wasted anyway and I and others have learned.

Ok,  I am not understaning again. 

IF the small 12v dpdt relay is at rest or latched position it is still providing power to the coil on the xx solenoid ?  If the small 12v dpdt relay is not at rest or in other latched position it is also still providing power to the coil on the xx solenoid?    That is wasted power.. so ideally we would like to eliminate the constant control power on problem. 

A small DPDT with a 3rd no contact position would be nice.

haemphyst :   Its a "latching spdt Big amps single coil relay (xx)    It has to be powered one way or the other as need by reversing the polarity.

He has a latching solenoid, when the coil is powered it clicks and locks in position A.  The only way to get it to position B is to reverse the voltage on the coil.  This clicks it and locks it in position B. 

I have not said anything about a relay other than the solenoid.  You asked for low part count, I said you should be able to do this with a switch.  All I have been talking about was a switch.  Then came the Paul Harvey line.  Now for the rest of the story.

Thanks for your efforts.. you did not waste your time.. everyone learned from you.. so cudo's to YOU !! !!   YOU DID GREAT ! THANK YOU < THANK YOU < THANK YOU !

it can drive 5 v directly but also it has a current limit.. we like to use one or 2 ports maximum because there are limited ports and we don't want to get into reassigning ports on the fly.  thanks.

FYI:  That would be a great product that is needed..  a one pulse using no control power anywhere in the system once latched.  Please let me know if you have any brainstorms.. mosfets are good for no power used when sitting idle..

In the name of Jesus Christ = Peace (not war) !

Your requirements are a bit vague, so it's hard to offer a complete solution.

If you want to use only one pin you will need to set the pin up as a normally high impedence input pin, then when you want to output a pulse you can output either a 0vdc ground pulse for one way (say off) and a 5vdc pulse for the other way (say on).

That will give you the logic needed to perform both functions from one pin.  What you do next will be up to the system designer.  You can run 3 transistors per function (3 on, 3 off - 6 total) to provide low current reverse polarity functionality or you could run 2 transistors and drive SPDT relays to provide your reverse polarity.

To do the transistor set up for the "ON" portion you will need 2 NPN transistors - the first one will provide your (-) output and the second one will bias the 3rd transistor - a PNP.  The PNP can provide your + output (either 5vdc or system voltage depending on application).  The "OFF" portion will need 2 PNP transistors - the first one will provide your (+) output and the second one will bias the 3rd transitor - a NPN.  The NPN will provide your - output.

You can then connect all the 4 outputs of the transistors to your solenoid.  You, of course, will need to size the transistors accordingly.  When the output pin of the uc is set to high impedence the circuit will take 0 current.  It will also be fairly stable because there will be no possible way both sets of transistors can be on at the same time (since they are triggered by the same pin).

The downside to using transistors is the part count will be kinda high as you will need multiple resistors and diodes to protect everything.  If you go with the two SPDT relay idea you'll still need a few resistors and diodes.  Unfortunately the more complex you make things the more parts you are going to need.

To do the two SPDT relay setup, like I said you will need two transitors - a PNP and an NPN.  The PNP will provide the (+) voltage for one relay (the other side of the coil will constantly be grounded) and the NPN will provide the (-) for the second relay (the other side of that coil will constantly be tied to voltage).  The common pins of the relays will be connected to your solenoid, the NC pins will be connected to ground, and the NO of both relays will be connected to voltage.  With this setup, whenever ONE relay is fired (and only one will fire at a time) the ground will be removed from that leg and replaced with voltage, thus creating a reverse polarity output from only one uC output pin.