Printer Friendly Forum Posts - push button start and relays

Let's see if any mad scientist out there can help. Car info: '02 Mercury Cougar, MTX. I am putting in a hidden push button start and doing away with the key. I have 95% of it figured, but I'm not great with electronics.

I am using a push on/ push off switch. When it is pushed on, it will bridge the 12v+, accesories, ignition and starter. What I need is an IC to kill the starter when it sees a tach or coil signal. I figure one relay to engage when power is intitially applied and a second one with a comparitor that will trip when a tach(or coil) signal of about 8v+ is detected in order to shut off the starter. Remote starts use the tach signal to stop the starter. They usually shut off around 600 rpm and I figure that is about 8v+ of the normal 12v+ to 14v+ the coil runs at.

Does any one have some made IC design skills? I probably could figure it out with the IC Op-Amp Cookbook, but alas, I am really damn lazy! Thanks in advance.

Only problem with the tach signal to disengage the starter is that the tach signal is (-) AC.

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Jeff
Velocity Custom Home Theater
Mobile Audio/Video Specialist
Morden, Manitoba CANADA

Yah, I know. You could use a Schmitt switch that can be set with a high low or just use the signal of the coil. That can be gotten around. I just need a IC that can be shut off with an external intput. Any ideas?

Why not just use a simple timer to crank the engine. You can adjusted and it will work just like a remote starter without the tach.

Thought of that one too. I have been bugging the crap out of a few buddies at the local Ford dealership. Fixed output times won't account for cold weather and what not.

Does any know what kind of curcuit or set up a keyless start uses? I don't know the layout of the gem they use, but that is basically what I am after.

Then why don't you just install a remote starter . Then when you press your switch it will take over for the remote starter .That way you will get the features of the remote starter like the keyless entry. And still have a car without an ignition switch. Also even if you get the circuit that you want you will need a way to manually crank the engine for emergencies and in those cases when the remote starter won't turn on the vehicle.

Thanks for the thought. There are a BUCH of ways to pull this off with two switches, or just hard wire a keyless start. I am actually going to us a transponder that will unlock the doors and disarm the starter kill when you are within 10 feet or so. I am aiming for the system used in the new cady and benz. I just cann't afford a custom $5000 to $10000 Seimens computer controlled system.

If anyone can do it, I would love the layout for the circuit in the factory gem or something like it.

Then why not just activate the ingnition when the doors unlock with the transponder. And just use a simple switch to crank the engine.

Ahead of you on that one. You would have to use a momentary to turn over the starter and kill it so it wouldn't grind (push button). It will start the engine great, so now you have to stop it...

Let me brainstorm tonight and I'll get back to you in the morning.

Cool. I have been kicking it around this week and the IC is the only way I can figure it out. If all else fails, I will do it with an on-on-momentary toggle switch for now. I guess I can eventually figure it out with some studing. Any ideas to do it another way or the describe about IC with relays would be great. Thanks.

Did I miss the part of this post string?

What are you trying to accomplish?

SI

yah, you missed it. check the first message. building a true push button start. no keys with only one switch - push on/ push off. need a ic with a comparitor to kill the starter when it sees the tach or coil output.

ok.

read the others. Tell me why you don't want to use a remote start unit?

Forget the remotes if you don't want to use them, a latched circuit (toggle or latching switch) will work fine if that is what you want to use.

The RS will take care of monitoring your coil, which seems to be your biggest hurdle.

It's cheap, easy and safer.

Getting around the auto shutdown is easy.

Let me know if you want to know how to configure.

SI

soundinstaller hit the nail on the head. By using a rs and disabling the auto shut off you can use the same wire to both start and stop the engine. A add-on rs will have a wire that goes to the existing alarm so you can use an extra channel on the alarm to trigger the rs. That will be your on-off switch for the car.

here is a quick idea,it will keep the relay on untill the input gets to 8 V, that is adjustable from 3.2 -> 9.6 V with the 10K pot, you would want to use a high power opamp if driving the relay right off of it unless the relay has a high coil resistance might wanna put a transistor in. Also this really will not do much you still have to add all the other circuitry, but thats my idea based around a difference amplifier. Hope this is of some use to ya.

posted_image

xetmes - that is the idea I am looking for. Now you have the variable input as a DC current. The tach is going to be AC; is this going to matter? Also, by the pot, you look to have put a cap. Is that right or is the picture missing something? What value is it, ect.

soundinstaller - I just prefer to keep the cost down with a $5 IC instead of a $25 remote start. Either way, outline it for me if you could and suggest a rm maybe. I figure you don't connect the switch for the brake kill, don't set the timer and hard wire the rf reciever to the push button to simulate a remote input. Question is, will you piss off the rs gem with a constant input from the bridged push button switch? Remember, there will be a constant input, not just a small fixed one like a remote pulse. Maybe/Hopefully I missed something. Like I said, outline it for me if you could so I can figure it out. Thanks.

ok i did i little more thinking, note this may not work at all, it would in theory and does in simulation, but that does not mean it will in real life, but just my ideas...

This will keep the relay closed from an input of 0V -> 8V, at 8V the relay will open and the connection lost.

posted_image

Okay, my symbol knowlegde is a bit rusty, so just a few questions. Zener - diode right? Okay, dumb, but what is the triangle. I for the life of me can not remember what the hell it means. I'll throw it together on my test board and try it out. Better there than burning out my car electrical system! Thanks.

yea i would HIGHLY recommend trying it out on a breadboard first, the triangle in the middle is a just an opamp, no special kind, just any normal opamp you get your hands on. yea thats a 4.7V zener, you could probably use a 5.1V also if thats easier, its just to limit current to the transistor. Good luck, let me know how it goes.. posted_image

Yo, soundinstaller. Any ideas on that rs? I think I would like to keep it in mind for a backup.

OK. Here is how I do it.

Never seen a RS that has a timer defeat, so I will tell you how I get around it.
I prefer the DEI piece (551T I think it is), but this config. should work with any starter unit.

First, you need something that will give you a latched circuit. I believe you said that you wanted to use a mechanical on/off. That will do it.

You will use that switch to send a constant ground to a pulse generator (dei# 452). You will use two outputs on this, one pulsed - output when ground is applied from your switch, and another pulsed - output when ground is removed.

The "pulse when grounded" output will go to your rs activation wire, and the "pulse when ungrounded" output will go to the rs shutdown wire.

In addition, the ground output from your switch will also trip an external relay cluster that will power your coil, and any accessory circuits that you might have.

To be clear, you will only be using the rs unit to crank the car initially, and for tach monitoring.

That's the basics.

Let me know if you have other questions.

SI