dual polarity relay circuit

Hi all I have been trying to find a circuit for a dual polarity momentary relay to trigger the power switch of a car pc it needs to trigger when the ACC+ line goes positive and then again when the ACC+ turns off so that the computer will turn on when the car is turned over then turned off when the car turns off the reason i want this is because i have a dual battery setup with the starting battery isolated from the accessories battery which is a SLA deep cycle battery the computer i want it to use standby mode but the problem is that it needs the power switch to trigger to turn on then again to goto standby mode i am not afraid to do any soldering/electrical work thanks in advance Scarfox

sorry i also forgot to mention that if you think it is needed my car is a 1995 Ford festiva WB

What PSU are you using for the PC? Many automotive-PC specific PSUs have such a function, eg Carnetix, OPUS, DSATX. M2- & M4-ATX etc, and they include a (programmable) delay after ACC or IGN off to avoid false shutdowns. (As well as low voltage cut-outs etc.) Years ago I published some simple DIY ideas in conjunction with my simple DIY battery isolator that used the alternator's charge light circuit (just add a relay). But even I'd probably have trouble locating those threads though they were probably on mp3car.com rather than on the12volt. Newer threads are easier to find because my DIY isolator became known as the UIBI (hence google "oldspark uibi"), but I think that was after showing its DIY add-ons. However the Relays section (see its link on this page's banner above) should have suitable circuits, maybe under its Relays / Special Applications link at the bottom of that introductory page. Reply again to ask if you cant find what you seek, or if you get confused. But probably the ideal solution is to use uPC type circuit - eg, a PICAXE (08M2 etc) or maybe one of KPierson's AT-Mega etc PCBs - so you not only program the basic behavior (rather than using cumbersome caps & diodes etc), but also add delays, voltage thresholds etc. There are other circuit possibilities too.

the psu is M3-ATX-HV i totally forgot that i could reprogram it thanks for your help i will try that