Here's what I've come up with... it's nothing new, or special, but it's definitely going to help me out while I'm at the beach this Spring Break... as I've come across many times where I've left my stereo playing too much and I've drained the battery.

To accompany my brand new 78series Optima Yellowtop, and alternator, I have created this module (not yet installed, but I have all the parts assembled.)


Stereo Control Module
Brain of Module: Pic microcontroller
Goals:
Battery Drain Protection
Keyless Stereo Operation
Remote via Car Alarm Operation

Connections:
Input to Module:
-Ignition 12v from car
-Accessory 12v from car
-Car Alarm Output - Latching Output from Car Alarm - Turn on Stereo
-Dome light wire from car
Output from Module to Head Unit:
-Stereo Ignition Wire (Turn-On)

Primary Functionality:
-Disconnect Ignition Power to Headunit upon reaching 11.0 volts, must stay
below 11.0 volts for 10 seconds.

Secondary Functionality:
-Run headunit after ignition is disabled, until door is opened, then closed,
(obviously unless the voltage goes below 11v)
-Allow stereo to run without key, (push to 'run', then within 2 seconds pull
back to "accessory mode". LED will start strobing to let you know its in
auto-run mode. You can pull key out of ignition and stereo will
keep playing, until: 1) Voltage drops below 11v, or 2) Key is inserted to
accessory/ignition mode for more than 5 seconds, and removed.
-Take latching output from car alarm to run stereo with no key. When activated,
the stereo will play, unless the voltage drops below 11v, when the alarm stops
sending the 12v signal, the stereo will turn off. During Remote AND Keyless
Operation, the Ultrabright LED will strobe at 5 times per second.

Things such as controlling windows and trunk, ignition could easily be accomplished, but I have no need really--the only thing I've thought of, is to have this module actually START the car when it gets low, to keep the party going all night!... but again, I'd have to figure out how to start the car... Anyone know if I can 'trick' my Viper 790xv into starting my car for me? Basically it would run the car for about 10 minutes, then shut off, the whole time the stereo plays uninterrupted. Once the battery gets to 11 volts, the process restarts.

Do you guys think something like this would sell, or at least be desirable? I've been to car audio shops all around town, and not a single one had ANYTHING remotely resembling this..

The parts to make one of these things is less than $30, including the relay to turn on the stereo.

 

anyone know if you can already buy one of these...?

 

You can all of the secondary functions that your talking about with 2 relays. for me anyway the shutting off at 11 volts sin't that important as I don't run my stereo that much with the car off.

 

Scrap, if you're most concerned about draining the battery, and are thinking about an alarm/remote start. I know the DEI remote starts (and most others) will give you a remote start input (-) wire. Having this go to ground is 'seen' by the brain as hitting the start button.
If it's setup for one press start, take it to ground ones and the brain starts the car. If you have it setup for two press start, take it to ground twice and the car will start.
If you think you can tackle what you’re talking about, you should be able to whip-up a circuit to trigger that wire and just start you car if the battery is getting to low (I would think 10V would work). Have the starter run the car for 24 min (with DEI, just go to a shop with a “bit-writer” and they can set it for any amount of time) to top off the battery and then shut down, the radio playing along just fine the whole time.
There are some safety concerns to watch out for.
First, I would put this on a switch and only use it when you need to use it. If you had an extra output from the brain, you just trigger a relay that would power the radio and this circuit. So you can take the keys out, hit the button, have your radio come on and have this circuit start to monitor the battery. That easy. Battery gets to low, car starts and runs for however long and shuts off, radio still going strong the how time.
Second, use a mercury hood switch. Most of the starters come with a hood pin switch. Throw that away and get a mercury switch. Those pin switches will rust and not make a good connection to ground. YOU DON’T WHANT THIS TO ACIDENTLY START THE CAR IF YOUR WORKING ON IT.
The remote starter will have a shut off switch under the dash, USE THIS IF YOU TAKE YOUR CAR TO A SHOP, OR IF YOU ARE WORKING ON IT.
I know this doesn’t meet all you’re needs, with the doors and all, but that can still be tackled later. I just think that if you were thinking about getting a remote starter, this would be the easiest, most seamless way to accomplish what you want. You could probably workout something with ‘dome light supervision’ to handle the radio staying on for some time after the car is shut off. I’m thinking of trying it once it worms up. That way the radio is on when you lock the doors and get in too.
Or, even easier then that. Just use a time latching relay, power the radio and windows for 30 seconds after you turn the car off.
I’ll have to check into how many channels you have with the 790xv, and see if I can find the circuit for you (I don’t feel like doing the math myself).

 

Just re-read your post. The white/blue wire is the (-) start input. Viper is DEI. Got any left over auxiliary outputs?

 

I did not install the alarm, unfortunately that was part of the price of the 790xv, but I have outputs for the door locks, and outputs for the trunk release, that's it.

I've read before that I have 6 channels, is that true?

I could easily program the circuit to start the car, I didn't know there was an input to start the car, that is great news.

Every time I take the car to the shop, I open the door, hit unlock-lock-unlock, which disables the alarm and remote start... at least I think it stops the remote start.. I do know that my hood pin works--and I agree, a mercury switch would be more reliable... I guess this would actually install on the hood itself, near the hinge, and when the hood opens it grounds the connection with the mercury?

I found this little guy but it's got so much info in it I'm a little lost.
790xv Installation Manual

I think I may buy a 'bitwriter' programmer.. because I'd love to be able to change things such as latching/timed/pulsing outputs... and I didn't see a way of changing that without the programmer

my trunk is controlled by holding down the AUX button for 1 second. Does that correlate to a specific channel? I was reading and it looks like you can change ANY button on the controller to any channel on the brain, but I doubt that Circuit City would have changed that up on me.

Right now my remote start goes for 12 minutes and shuts off, seems long enough to charge the battery, but maybe if I had the programmer I would set it to 20 minutes.

So you just need to pulse a 12v signal to the white/blue wire, and the brain takes this as an initiation to start the vehicle? (I'm assuming this is used for factory alarm integration... and the GPS module)

It's interesting to learn of the different configurations the channels can have, such as staying latched as long as it recieves a confirmation pulse, things like that... plus timing the output.. pretty neat. I really don't care what kind of output the alarm has though, because I can easily reprogram the circuit to respond differently... if its simply an output pulse, or if its a latching signal, it's not really important

Thanks your for help NEEDAZ

 

plus what's the deal with the "channel expander" that I've read about, which can give me an additional 6 channels or so...?

heh reading through this manual leads me to believe that Circuit City left out quite a few things... such as remote start disable switch, as well as tachometer-sensing remote start kill...

I've remote-started my car and then pushed the accelerator pedal down... the car does not shut down...

I guess I should check to see if they even put in the nuetral safety switch signal... I bet my car will start in gear... or will it? My key won't start the car in gear...

 

1=It looks like you have at lest one extra channel to use. See P12 H2/3, If I remember right this output will be triggered by hitting the ‘Aux’ and ‘lock’ button at the same time, Could be Aux and unlock. This could be your “turn on power to the radio and windows” output. The trunk pop is probably channel 2- P7 H1/12.

2=You don’t need a programmable circuit to do this, just an op-amp and some other goodies. I’ll see if I can find the circuit.

3=Do NOT really on this method. Remember that if someone’s got the finger on the belt and the car tries to start, bye bye finger. This is NOT something to take a chance on. I would add a shut off toggle switch. See P15 H3/3, H3/4, and H3/6. These are all shut-down inputs. The (-) means it’s active when it goes to ground. (+) means it’s active when it goes to B+. A toggle switch to ground on pins H3/3 or H3/6 would work as a “remote starter lock-out”. Or a toggle switch to B+ and pin H3/4 would work.
DON’T trust the pin switch. Go out and get a mercury switch. Come on man, this is a SAFETY thing, don’t skimp. And Yes, that is exactly how to install it and how it works. It will have two wires, one goes to a GOOD GROUND (remember all my renting about good grounds?) and the other goes to pin H3/3, (Note the (-) at H3/3, this means a ground trigger).

4=Print it out, read it, know it, love it. When your done loving it, read it again.

5=You don’t need a bitwriter to change most of those things. Read P25 and P26, these are of your options. You only need the bitwrite to change the ones with the PIC of the bitwriter. The others are programmable by the key fob. Read the manule.

6=Don’t mess with changing the buttons around, that’ll just mess you up down the road. Also re-read response to 1 for aux channel.

7=See P26. You can select ether 12/24/60 min run time. With the bitwriter, you can make it any time you want, as long as it’s no more then 60 min. I would do 24, that’s where my truck is set.

8=Not a B+ pulse but pulse it to ground (Note the (-)). If you have to press the start button on the remote one to start the car, this needs to go to ground once to start the car. If the need to press the start button on the remote 2 times, this needs to be pulsed to ground 2 times. Get it?

 

9=If you get a channel expander they work off of one of you existing channels. For every time you press the button on the remote, that corresponds to a channel/ or aux device. So, if you put the channel expander on the aux out of you brain, where the trunk pop is now. If you hit the aux button once, that is channel one active, or in this case trunk pop. If you press the button 2 times, that channel 2 active (say window rollup), if you hit the aux button on the remote 3 times, that’s channel 3 active (say your “turn radio and window power on” output). Get it?
Also, most of them will let you program the output type. Like pulse, latched, latched timed, latched re-set with ignition.

10=Most shop only include what’s needed to make it work as part of the install. Anything extra is extra. You need to ask for it and you need to pay for it. I think this just shows how bad some of these places are. They have the opportunity to charge for more labor, and make the customer happy because now they got all the extra stuff too. I love it when you can charge more, and still have a happy customer. That money they lose out on. This is part of the reason you get better service at a small shop. They will take the time to explain all the extras and talk you into them.

11=The tach input may still be used. It only looks at the tach signal at start-up. Once it “sees” the vehicle is started, that input is ignored. It’s just for over rev on start-up. And they may well have it setup for voltage sense. In this mode the brain looks for the 13.5V or so you get for the alt. to know the car is running. It’s easier because you don’t need to run that wire through the fire wall.

On my truck, I have the dome light on one aux channel, and 4 100W spot lights one the other. I don’t like dome light supervision turning the lights on every time. And I can light-up the backyard and see if the gate is closed before I let the dog out. It works for me.

 

ah, about the dome light supervision... I wish my car did that(keep the lights on after I get out, or unlock via remote)... I would assume that if the alarm can 'sense' that the dome light is on, that it could apply power to run the light as well? I'm no pro on the door pin and domelight wiring setup, especially when you stick alarm in there somewhere..

to have domelight supervision would I have to use another output from the alarm?

Now I am kinda curious, later this week I am getting the window up/down module installed, and I want to manually control the windows, not with arm/disarm... for example, I don't want the windows to roll down when it's raining outside, even though I disarmed the alarm... so I wonder how they are going to set that up without the channel expander.. it seems that I'm already using 2 of the channels for locks and trunk... unless those don't count against the 'six' that I supposedly have.

I really just need to pull the brain down from the dashboard and get a multimeter and try all the wire outputs from the alarm, to see what they do when I hit certain buttons on the remote... although I have a feeling that CC actually cut off the wires not being used, so I'd need a new harness I bet.

and you say that a simple op-amp and some other goodies can accomplish this? Do you mean to have the car alarm turn on the stereo, or to have the keyless radio control?

One other thing, if I had the key in the ignition, set to 'run', and the stereo ran down to 11v, I would want the car to be able to start itself... but would the alarm be able to shut off after 24 minutes with the key in the ignition, or will it just stay on? I think it would... I guess I would just make sure to only use this module if I have the key in the accessory mode.

 

12=Come on man, you didn’t listen about reading the manual (see response to #4). P7 H1/4. Then on P9 they show you how you need to hook it up with a relay, (Note it’s only a 200mA output). READ.
Get a copy of the owner’s manual too. Read that, then re-read the install manual, then re-read the owner’s manual, then re-read the install manual. I know it’s not written all that clearly, but you just have to work through it. You’ll get to a point, once you’re use to how they refer to things, that it all just clicks.

13=you’ll have to talk to them about that before they start the work.

14=That may help you to understand how things are working under there. But do this AFTER all the reading, so you know what you’re playing with.

15=The op-amp is used as a comparator. This is what you would use as a low voltage trigger. Then some 555s or a 556 to handle the ‘pulses’ that would tell the alarm brain to start the car. Not to be an a$$, but if you had to ask that question, you may want to re-think whether you should tackle this project. Is there someone you know that can help you with the design of things? This isn’t just an easy “do this to get it to work” kinda thing. I’ll help point you in the right direction, but you have to be able to run with it. I’m not going to do the engineering part of things for you. H3ll, I’m not even going to do the engineering part of it for me. I’ve got it in my head. When and IF I do this, I will just bread board it, get the bugs worked out, then build and install. IF you can’t work through these things on-the-fly, you may need to find a friend that can, or re-think the project. I don’t mean to be harsh.
There are a lot of thing to take into account here. For instance, you don’t want this circuit active if the car is running. Why, well if your going down the road and the alt. goes south on you, once the voltage drops you’ve got this thing trying to start the car.

16=With the key in the ignition, the car will keep running after the 24 min. That’s why I would use the channel 4 output (see response to #1) as the trigger to turn on the radio and this little ditty. You would not need (or want) the keys to be just hanging out in the ignition. Pull the keys out of the ignition, press the right buttons on the remote, have the radio and battery monitor come on at the same time. What I'm thinking here is, take the red (switched) wire from your radio to a relay, then trigger the relay with ether the Acc circuit in the car, or the channel 4 output form the brain. This relay would then turn on the radio (with the red wire to the radio), and this battery monitoring circuit. Maybe a second relay to power the windows too, so if you’re radio is on with the channel 4 output, the windows can be rolled up or down.
For real fun, if you have an overhead console, integrate and IR repeater. Then you’ll have no problem using the HUs remote to control the stereo while you’re sitting on the beach.

 

Check out this circuit. It’s designed for vary low current, 6mA/15ma. Some of the parts can be substituted for the more common non-low current stuff. The first part of the circuit is the important part for you. U2, U1, and Q2. U3 and U4 would need some work. Set them up for the double pulse then another transistor to do the switching to ground. Run that into the (-) start input.

http://www.solorb.com/elect/solarcirc/lvbeep/index.html

 

cool, and the reason I haven't had much experience with custom circuits and such, is I really enjoy messing with microcontrollers.. haven't had time to get into all those neat custom circuits. I have a few proto boards laying around, so I will just go ahead and use that for the 'circuit'... but I'm still going to look into that op-amp comparator setup... I may need it for something in the future.

If I didn't have a proto board I would have just used a pc board and soldered straight to it, like I've done for my LED boards, this just happens to be very convenient.

I think what I'm going to do, is that the low battery protection will be enabled ALWAYS. So that if the alternator did die on my while driving, all it will do is kill the radio. I will make it so it only restarts the car when the unit is in keyless mode, as you suggested.

This is probably in the manual, but what would the alarm do if the car was already running, and it recieved a signal to start the car(via white/blue wire)? I would assume it would just go into valet mode, same as when you use the transponder to trigger a remote start when the car is running.

And that is a great idea on the ir repeater. I've thought of this but I've never pursued it enough. Sure would be convenient to have an RF remote that can actually go some distance.

 

You enjoy messing with microcontrollers? Have at it, I think there a PITA. Give ma a bread board any day.

 

To give you an idea of what I have in the works... my brother works for a company that makes a GPS/cellphone system... allows this device to be placed in vehicle and the information is sent via cell to a server.. so besides all that gps stuff, the device uses a pic microcontroller... it can be completely integrated into the car alarm... when I really get this thing going, I'll learn all the alarm outputs and inputs and have them controllable via cell phone, (sms msging)... or you could track your car if it were stolen...

basically its the gps unit that DEI makes, but a whole different company, and much, much cheaper, since I can get one at cost.

my goal in life is to have my car stolen, (probably won't happen to my 3rd gen,) then chase down and beat the sob to death... we all have our dreams, don't we?

I like the idea of being able to monitor the car via SMS since the 2-way transponder is pathetic... I could be across the world and find out if my car is getting broken into, call the police, friend etc... I would just make a specific ringer for when the car msgs me, like an alarm...

The only thing that bothers me about all these microcontrollers, is that the police are coming out with devices that can disable vehicles by destroying their computers, via microwave technology. That would destroy so much in so little time... I'd hate for cops to accidentally use that on my car...

 

let me know when you get a wiring diagram