This Circuit is intended for ATX type motherboards only:




This plan was originally designed by Jeff Mucha, I just built the first prototype.

Now he is making these at limited quantity and selling them for $23. It' much smaller and better quality than mine :)

You can check out his URL here









First in WinMe or W2k go to control panel -> power options and set the computer to shutdown or hibernate when power button is pressed.

When you turn off the car  the computer waits whatever time (C1 and R1)

then sends an atx power pulse for whatever time ( C2 and R2) telling WinMe to

hibernate or shutdown. After some time (C3 and R3) the relay cuts power to the PSU or inverter.

If during the first delay you happen to turn the car back on, nothing happens.

If car is off and you press the momentary switch, car will go into immediate shutdown or hibernation.

If car is on, the momentary switch acts like the computer power switch without cutting off the power.

The main power switch is there if you don't want the computer to automatically turn on whenever you start the car ( for those times when you valet your car)



Parts List:

Symbol    Quantity    Part #       Digikey Part #         Description

   D                4         1N4148    1N4148MSCT-ND   diode

   T                2          3904        2N3904-ND             NPN transistor

   IC               1          74HC14   296-1577-5-ND       Hex Schmitt Inverter 14dip

   VR              1          7805        296-11108-1-ND    5V Linear Voltage Regulator (heatsink not necessary)   

   Relay          1          any SPST or SPDT 12V 30A relay

   LED           1           any Radio Shack or Computer LED will do fine

   Resistors   2x10k ohm, 1x1k ohm, 1x3k ohm, 1x 100ohm



 For  C1 to C3 and R1 to R3:

 Figure out how much delay time you want by using  Time(seconds)  = Resistance (ohm) X Capacitance (farad)

 You can use variable resistors (pots)  to adjust the time without having to change resistors or capacitors.


Here is what I used:

 C1= 680uF   R1= 1Mohm pot      0 ~ 11.3 min (delay before telling computer to shutdown)

 C2= 27uF     R2= 200kohm pot   0 ~ 5.4 sec (ATX power switch pulse)

 C3= 680uF   R2= 200kohm pot   0 ~ 2.3 min ( delay for computer to shutdown)


My order from


     QTY     PART#                         DESCRIPTION                                  EACH      SUBTTL
 1   10   1N4148MSCT-ND    SW RECTIFIER 0.15A 75V DO-35               0.05300   0.53 
 2     1   296-11108-1-ND     POSITIVE-VOLTAGE REGULATOR/LINEAR  1.02000   1.02 
 3     1   MBRB3045CT-ND    SCHOTTKY DIODE 45V 30A SMD-220        2.60000   2.60 
 4     2   4007PHCT-ND         CAP 10V 680UF ELECT AXIAL                    0.53000   1.06 
 5     1   P10319-ND             CAP 27UF 50V ELECT FC RADIAL               0.47000   0.47 
 6     1   4LG16BK-ND           POT 1M OHM 6MM CERAMIC TOP ADJ       0.59000   0.59 
 7     2   2N3904-ND             NPN SML SIG G.P. AMP&SWITCH TO92     0.26000   0.52 
 8     2   4LG25BK-ND           POT 200K OHM 6MM CERAMIC TOP ADJ    0.59000   1.18 
 9     1   296-1577-5-ND       IC HEX SCHMITT-TRIG INV 14-DIP           0.56000   0.56 
 10   2   10KW-1-ND           RES 10K OHM 1W 5% METAL OXIDE           0.19000   0.38 
 11   1   Z208-ND               RELAY PWR SPST 30A 12VDC W/QC            3.70000   3.70 
 12   1   1.0KW-2-ND          RES 1.0K OHM 2W 5% METAL OXIDE          0.23000   0.23 
 13   1   3.0KW-1-ND          RES 3.0K OHM 1W 5% METAL OXIDE          0.19000   0.19 
 14   2   S2105-02-ND         CONN HDR 2MM 2POS VERT GOLD             0.44000   0.88 

Subtotal: 13.91
Handling: 5.00
Total $18.91


Here is some data on the controller:

This is a pic of what it looks like.
notice the ch1 is Agnition ch2 is atx pulse and ch3 is relay



This is a pic of what it looks like if you restart the car. The power to the relay doesn't change.