4-way Power Control Switch

**Jarrod** · 12-06-2005, 09:53 AM

Hi Guys, I'm looking for a little help with a schematic I'm designing for controlling power to my CarPC.

I've attached the schematic below, and this is what I'm trying to do:

Have a rotary switch (1-pole, 4-way) that controls how my CarPC startsup and shutsdown. Basically, the relay#1 is there to cut power to the 'momentary to constant' circuit, so when ACC is powered, the 12V constant output from the door unlocking goes low.

Then when the car is turned off (ACC goes low), the carPC will shutdown. All this only happens if the switch is in position 2. I don't need the carPC to go off when I lock the doors, so this should make the schematic a little simpler.

In position 1, the carPC is always powered directly from the battery.

In position 2, carPC goes on when doors unlock, and off when ACC goes off.

In position 3, carPC goes on and off with ACC.

In position 4, carPC is always off.

Basically this is just a switch so that I can use carPC without the keys if I want, start the carPC as i walk to it and unlock the doors, start normally with ACC and stay off completely (say if I put the car in for service).

I am basically a newbie to drawing up schematics, so I'm sure there are some major problems in there somewhere, so please let me know!

This is the rotary switch I plan to use: http://www.altronics.com.au/index.as...=item&id=S3021 (with the switch configured for 4 positions)

And I got most of the schematic help from here: http://www.the12volt.com/relays/page5.asp (momentary to constant output diagram)

Also, this will be connected to a M1-ATX (SW connection) powering my system, so shutdown controller is built into it, as well as low-battery detection.

**Jarrod** · 12-08-2005, 07:26 PM

Taking another close look at the schematic, I think the output of Relay#1 should be connected to 87a if I want continuity whilst no charge is going over the coil?

Anybody?

**PatO** · 12-08-2005, 11:36 PM

Amazing, dude! You've just solved the main problem plaguing my system! How to keep it on reguardless of the state my car is in.

I think you'll need to put a cap prior to the PS to take up the slack during rotations of the switch. And I'm not familiar with the M1-ATX, but are you connecting the circuit to the direct 12V (high-amp) terminal, or to a relay which provides the juice?

**Jarrod** · 12-09-2005, 07:41 PM

Thanks for the cap suggestion, thats another issue that I wasn't sure about when changing switch positions.

What value cap should I put in there?

The M1-ATX has a SW connection which basically tells the powersupply when to startup and shutdown the PC. This connection doesnt actually power anything, so doesnt need to draw much current at all.

The 'juice' is actually supplied directly from the battery at all times, no relay at all.

I've got no idea if the circuit will work or not, so how are you with electronics? Will it work as intended?

**binary.h4x** · 12-09-2005, 08:07 PM

1,3,and 4 will work but position 2 has a flaw.

If the doors are unlocked, the ACC will probably be off. If the ACC is off, Relay 1 will not allow current from the battery to pass through to your momentary-to-constant circuit.

**binary.h4x** · 12-09-2005, 08:12 PM

Originally Posted by Jarrod

Taking another close look at the schematic, I think the output of Relay#1 should be connected to 87a if I want continuity whilst no charge is going over the coil?

Anybody?

Just noticed this post, yes to fix it, relay 1 needs to have the momentary-to-constant circuit affixed to 87a

EDIT: this might help

I also added a 4700uF cap. It should have no problem covering any dips in voltage that will occur from your relays switching on and off and the switch having position changed. You can buy this cap at Radioshack.

**Jarrod** · 12-09-2005, 09:25 PM

Thanks for the help, much appreciated. My main concern was the use of the diodes. I added them where I thought was required, but wasn't completely sure.

Also, do all doors have a -ve pulse when unlocking? Just wondering coz I haven't actually tested my car yet. Any suggestions on the easiest way to test for -ve or +ve pulse from my remote door unlocking?

If I find its a positive pulse, how will this affect the circuit?

Thanks again for all the help!

**binary.h4x** · 12-09-2005, 09:34 PM

Originally Posted by Jarrod

Thanks for the help, much appreciated. My main concern was the use of the diodes. I added them where I thought was required, but wasn't completely sure.

Also, do all doors have a -ve pulse when unlocking? Just wondering coz I haven't actually tested my car yet. Any suggestions on the easiest way to test for -ve or +ve pulse from my remote door unlocking?

If I find its a positive pulse, how will this affect the circuit?

Thanks again for all the help!

I'm pretty sure all that you would need to do is change pin 85 on Relay 2 to ground.

**Jarrod** · 12-09-2005, 09:57 PM

Ok great, that's what I would have guessed. Any suggestions on where to test this in my car? Would i be able to test at a fuse box or would I have to open up the car door and test at the lock?