Low Voltage start

OK, heres the deal and what I want to do. I have a mult battery set up using an isolator in my car. I also have a car starter in my car with a negative activation input. What I want to do is set it up so when my rear batteries voltage drops to a certain point it will send a signal automaticly to the starter to start the vehicle. That way my batteries never really die. I was thinking I could hook up a voltage gauge on the rear batteries with a dummy light that came on when the voltage droped to a certain point. My only problem is I have been unable to find a voltage gauge that has a dummy light in it. Does anyone have any other ideas or know where I can get a voltage gauge like the one I described.

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double-secret reverse-osmosis speaker-cone-induced high-level interference distortion, Its a killer

EDIT:...that link isnt gonna work... go to www.selectproducts.com and click on products/digital guages/then voltmeter

*Display “Flashes” when reading is higher than the set point. *   Only thing I could find fairly quick.I'll do a little more research when I call my homie up to order a few parts.   sS

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RTFM

What alarm/rs are you using?

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Certified Security Specialist
Always check info with a digital multimeter.
I promise to be good.
Tell Darwin I sent you.

I've been sick lately, sorry I won't be on much.

First thing to know is if there are enough safeguards to prevent it from starting up when it's not safe to do so; is your start trigger going to take care of things to check for hood open/closed, in park, etc? A setup like this needs extra safety, since it doesn't need any manual intervention on your part like pushing the remote start button-
If you have that taken care of, you could just use a voltage comparator like an LM239, to trip when the voltage falls below your threshold setting. Draws next to no power in standby, so it doesn't drain your battery. From there, it depends what you need, whether a momentary start pulse or a simple continuous signal.

comparator datasheet

There's the datasheet for the comparator; only about 25 cents, so it's pretty much free except for your time-

You'll be using the basic comparator diagram setup, just add a few resistors to set up your voltage threshold to a 12V reference or whatever you want, and you'll be set-

Also, you might want to add zener diodes for the reference voltage if you need it to be more precise, if your primary battery voltage fluctuates too much for a stable reference from just a simple resistor divider-