Trunk Popper into Car Starter

**PatO** · 12-27-2004, 05:58 PM

Just got a Viper 562t car starter installed and it has a trunk popper lead (AUX button on remote) I'd like to use to start my ATX computer. The computer will always have constant 12V power from battery, so I need to trigger the 12V power switch pins on the mobo.

Problem is that the starter outputs a -12V (200mA) signal. The amperage I'm not worried about - more than enough, but how do I turn negative into positive?

Here are two options I've identified:

1) Use a relay. Seems like overkill for a few hundred milliamps being triggered for a second or two.

2) Since the starter output is negative, could I wire it directly to the mobo pow-on positive connector? Would a mobo require current through the negative connector?

Does anyone else have any ideas?

**EBJUSTIN** · 12-27-2004, 06:21 PM

You probably could tie it diectly to the +pin of the PWR_SW header on the mobo however I would still use a relay. You can use a small 12V 2A relay, they are much smaller than the typical 30A relays. Connect one input of the relay coil to 12V from the battery and connect the other end of the coil to the output of alarm. Connect the 'normally open' pin of the relay to ground and connect the 'wiper' pin of the relay to the +pin of the mobo PWR_SW. Keep the 'normally closed' relay pin floating. FYI, the Carnetix and possibly the OPUS have a dedicated input to connect a car alarm output to for remote starting the carputer.

**Peoples** · 12-27-2004, 06:22 PM

sounds like an awesome idea......if you get that working, please post diagrams on how you did it. I'd love to try that in my install.

But i thought you'd just want to jump the pins on the motheboard, wouldnt sending it current fry something?

**PatO** · 12-27-2004, 06:36 PM

Thanks!
That's probably what I'll do. Grab a small relay at the rat shack.
I've attached the diagram in the manual.
85 - (-) starter AUX feed
86 - (+) from battery
87 - (+) term on pow-on on mobo
30 - (-) term on pow-on on mobo

Don't know if the pinouts will carry over to a small relay, but that's the idea.
The starter triggers the relay for as long as AUX button on my remote is held, so I don't need to worry about any momentary circuits.

**Peoples** · 12-27-2004, 06:50 PM

lol, well tell me if it works before i go and mess something up

**EBJUSTIN** · 12-27-2004, 07:58 PM

Originally Posted by Peoples

sounds like an awesome idea......if you get that working, please post diagrams on how you did it. I'd love to try that in my install.

But i thought you'd just want to jump the pins on the motheboard, wouldnt sending it current fry something?

You would not be sending any current to the mobo. The alarm/trunk pop signal is active low, so it is basiclly just connecting a ground to the relay coil. The wiper of the relay will just short the PWR_SW signals on the mobo. It's the same as if you manully pressed the PWR button.

**EBJUSTIN** · 12-27-2004, 08:02 PM

Originally Posted by PatO

Thanks!
That's probably what I'll do. Grab a small relay at the rat shack.
I've attached the diagram in the manual.
85 - (-) starter AUX feed
86 - (+) from battery
87 - (+) term on pow-on on mobo
30 - (-) term on pow-on on mobo

Don't know if the pinouts will carry over to a small relay, but that's the idea.
The starter triggers the relay for as long as AUX button on my remote is held, so I don't need to worry about any momentary circuits.

Looks good, when you get the small relay just use an ohm meter to figure out what pins are normally open/closed. One more thing, you should place a diode across the coil (pins 85/86) for reverse currnet protection.

**blazinlow** · 12-28-2004, 02:53 AM

Ive done something similiar. I have my computer turn on when the car has remote started. My alarm sends ground pulse to a wire coming out of the brain after it has sucessfully started.

85- wire from brain
86 - 12v
30 - One pin of the power on header
87 - other pin of the power on header

**PatO** · 12-28-2004, 05:33 PM

Sweet.
Thanks for your posts guys. I just installed the computer in the car last night and am fine tuning some more of the tricky bits - ground loop, display mount, dual battery. This is #4 on my list, so I'll get to it in the next day or two. I'll be sure to take pictures and write up details when I get it working!

**MatrixPC** · 12-30-2004, 12:53 PM

I also use alarm to start my computer. Basically this is what I did.
A small 12V SPST relay. Although the pin # is different that the standard auto relay but the idea is right there.
86 and 30 to 12V from battery.
85 to alarm (-) aux output.
87 to SDC ACC wire.
The SDC ACC wire also connect to the car ACC wire. Since the car ACC wire and pin 87 are join to the SDC ACC, both of the power source has a diode inline to separate the 2.
work like a charm.
BTW my alarm only has 2 channel output. I use one for remote starter, and the other for window roll down. I have to buy the channel extender (or whatever they called) to add 2 more aux output for a total of 4. Now I can use all 4 (Remote starter, window up, window down, PC). Cool isn't it?