power switch circuit help (on/off/auto modes)

**jiggersplat** · 12-02-2006, 10:00 AM

all,

i'd like to mount a switch in my dash that controls my carputer. i'd like it to have 3 modes, auto, on and off. i'm using an m2-atx power supply.

the behavior i would like is as follows:

on - IGN lead of M2 connected to battery, computer is on even when the car is off
off - IGN lead of M2 grounded, computer is off even when the car is on
auto - IGN lead of M2 connected to IGN of car, computer is on iff the car is on

i have a 3-way switch that is on-off-on. my plan is to wire one "on" pole to the battery, one "on" pole to an ignition switched 12v source and the "off" pole to the IGN lead of the M2 with a pull-down resistor in parallel.

Code:



         ON  OFF AUTO
BATT ----o    o    o----- IGN
          \
           \ 
            \       20K
  M2-ATX o---o---\/\/\/\---> GND
     IGN

will this circuit work?

secondly, am i correct in assuming that the M2's shutdown delay will prevent the computer from shutting down as i switch from ON to AUTO or vice versa?

**com2soft** · 12-02-2006, 09:01 PM

the ACC wire in M2 control its auto. disconnect it makes it manual. in Manual you need a manual switch (connect to your mobo) to turn on/off pc.

**TheLandYacht** · 12-04-2006, 10:44 PM

but in answer to your question, the setup you're talking about is EXACTLY as I have it in mine...minus the 12v psu...

Got that 3way switch on my dash for times when I need to turn the car off for a couple seconds (if the van's engine dies & needs to be restarted for instance, I don't have to cycle the puter).

**walky_talky20** · 12-04-2006, 11:19 PM

Yes, your circuit will work, but I don't believe that it is necessary to ground (or pull to ground) the M2's IGN wire. Simply leaving this wire open for "OFF" mode should do the trick. (If you know something that I don't, please let me know because I am planning on doing this as well). And yes, the delay of the M2 will allow you to switch from "ON" to "AUTO" without the PC shutting down.

**jiggersplat** · 12-05-2006, 08:14 AM

it may not be necessary but it seems like in general leaving an input floating is a bad idea just from an engineering perspective. does anyone know for sure what the M2 does when that lead is floating?

**MatrixPC** · 12-05-2006, 09:24 AM

Just get a ON-OFF-ON 3 pin toggle switch.
Pin 1 connect to battery
Pin 2 connect to the M2 ACC wire
Pin 3 connect to the car's IGN or ACC source.

Operation:
First ON, PC will be on untill the battery flat
OFF, well, it off regardless of car's status
2nd ON, PC on with the iGN key.

No extra component needed.

**GizmoQ** · 12-05-2006, 10:17 AM

**roleary** · 12-05-2006, 12:19 PM

jigger -

i use an on-off-on switch. wired it just like MatrixPC recommended. when the switch is in the down position, the computer reacts to the ACC line. when the switch is in the up position, the computer is on. when the switch is in the middle position, the switch is off.

it works great.

- O

**SUVputer** · 12-05-2006, 01:49 PM

I have the exact same installation .. on-off-on switch!

the m2-atx handles it just fine! you don't really need to ground the "off state

**treetop777** · 12-05-2006, 05:32 PM

Anybody care to post a diagram, please.

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