Latching Relay Circuit For Car Alarm to Work with Remote Start - Page 1
Forum section: electronics / projects

author: Falcon69
author_rank: Super Contributor
timestamp: July 04, 2017, 07:13:30 am
content: Okay, so here's the dealio...I got a new truck, and unfortunately, it's on the top 5 most stolen vehicles list across the nation. So, I Just bought an alarm I need to install. I've installed alarms many times, however, this part that I'm wanting to do is all new to me.The alarm comes with starter kill, that's all fine and good for a new would be thief, fbut for a veteran, it's easy to bypass. So, I want to cut the main leads going to the FICM (Fuel Injection Control Module) and put in a cut-off switch that would be hidded. This won't allow the truck to start. It would allow it to turn over, if they were able to bypass, but never start, as the fuel injectors will not fire. I know, most of you are saying just wire up a switch to the Fuel pump...well, great...if I had a gas car. This is diesel, and cutting off the fuel for diesel is always bad, as the injectors will always try and fire. That's bad and will destroy the injectors at a cost of $300 a piece, not too mention the labor to repair.So, The problem is with the remote start. And that is not the only problem. I want to wire the kill switch for the FICM as a "hall Effect" style by use of a magnet, that way I can hide the switch part of it way up somewhere behind the dash that can NEVER be seen, and then all I have to do is wave the magnet close to it to trigger it. Then, have it trigger a relay which latches and then start the truck and it keeps the connection (power to the FICM) until the ignition is turned off, then the latches closes again and the truck can then be rearmed.Then, when I remote start the truck. it activates that same relay, doing the same thing as if I had waved the magnet close to the switch and so on.But, I'm not quite sure how to go abouot it. I've been thinking about it for the last couple months while I've been saving up for the alarm. Can't quite figure it out.I'm also wandering what happens when I remote start the truck, disarm alarm (i think it still keeps engine running, it just turns off alarm part and unlocks doors), get in, insert key, and turn to on position, that slight turn to the on position, will it mess with the latching relay and quickly turn off the FICM? That could damage it if it's done too many times or something?Anyway, any help would be great.I already have the hall switch figure out. It allows whatever is plugged into it, to sink to ground through a mosfet. So that isn't a problem. I just have never dealt with latching relays.I think to bypass the remote start and FICM kill switch, i would use a diagram like one below? If so, then I just need to figure out how to build the latching relay part for the hall switch that connects to the FICM and figure out how to combine the two circuits to work together.Thanks in advance for any help you guys can give this newb.EDIT: Ignore where it says fuel pump relay on the diagram, that should read for the connections from the latching relays of the hall switch for the FICM

author: Falcon69
author_rank: Super Contributor
timestamp: July 04, 2017, 07:21:13 am
content: Just got to thinking, that diagram will probably work, the only problem is though, I will need it to latch, because I'm not going to sit there and hold that magnet on the hall switch. Also, it will need to turn off when I turn off the engine with the ignition. But, like I said above, also be able to turn on the FICM with the remote start as well.

author: Falcon69
author_rank: Super Contributor
timestamp: July 04, 2017, 06:32:07 pm
content: Okay, I worked on it all night with the help of using Falstad's Circuit simulator. I know, it's not the best, but works pretty good to visually see what happens for the most part. And this circuit seems to work in the program, except for a few concerns, which I will point out.Hopefully someone with more experience can chime in here.First off all, the Alarm I bought is a DEI Viper 5706V with a Remote Start and a DEI Xpresskit PKALL module so it works with the year of truck for the remote start thing. A lot of new vehicles require an add-on module for remote start because of the security features and stuff built into the truck or tach options or something.The truck is a 2007 F250.So, the circuit is below. It's seems pretty simple. 6 relays, and can all be standard 12v 40 amp relays (which I have plenty of on hand). I didn't drawn in fuses, but there will be on all the battery inputs, of course.So here's my questions for the more experienced alarm guys.1. When remote start is activated (i.e. in my house, I click button on remote, it starts to warm up engine when cold) and then I go get in the truck and place key in the ignition, does the alarm then recognized the key is in the 'ON' position and it cuts off the flow of the remote start part of the alarm? This is how I designed this relay circuit. However, it doesn't seem to make a difference if the remote status wire stays active or not. Also, the circuit is designed for a +12volt input from that remote start status wire. If it is negative, then I will need to invert it or redesign the circuit somehow. I'm not sure what it is on this alarm yet.2. I've noticed, for example, that if the remote start is on, I get in and place the key to the 'On' position, as if I'm going to start driving, and then the hall switch is activated, it shuts the FICM off. I guess this isn't a big deal, as long as I don't get the magnet anywhere near the hall switch while driving, but if it does get close by accident, it could be real bad when I'm on the freeway or something. I tried to think of a way to prevent that from happening, but I can't figure it out without it affecting something else in the circuit.This circuit seems to work except for what is noted above. Even with alarm on or off, turning ignition on does NOTHING to start the truck, unless the hall switch is activated or the remote start from the alarm. And this circuit allows me to just hold the magnet close to the hall switch, start truck with ignition, then pull away the magnet and go on with the driving. I like it. But again am worried about #2 question above.This would be great if I can get this working. It would take a would be car thief some time to figure out what is going on with the truck, as to why he can't drive it off, as long as I'm sneaky about how I do the wiring, he'll never figure it out without spending way too much time. By that time, he'll just move onto to an easier target (after he gets pissed off and takes his screw driver and tears up my leather seats like they always do).

author: Falcon69
author_rank: Super Contributor
timestamp: July 06, 2017, 05:26:22 pm
content: nobody has any advice or suggestions on this?I get most of the alarm components delivered today, and I'm eager to install it.I plan on hacking off all the wires to the alarm as well, and changing them all to a single color, just to make it alittle harder for wouldbe thieves to figure out what goes where should they have experience in alarm installing and want to steal my truck.

author: Falcon69
author_rank: Super Contributor
timestamp: November 18, 2017, 02:56:31 am
content: Well, I finally had the time to design this thing, order the boards and components, and assemble it.I have not yet had a chance to test it yet to see if it works.I have asked local car stereo shops/ Alarm shops if there is a manufacturer who makes this. They have told me no. I would have rather bought it, of course. DEI, the major alarm accessory manufacturer, does not make it either.Here is how it is suppose to work.......With Car Alarms on the market today, you are limited to either having a Remote Start, or a manual cut-off switch which can be used on the FICM (Fuel Injection Control Module, for Diesels), FUel Pump CUt-Off, or any other accessory controlled with a relay.........But NOT both. The reason for this, of course, is that the remote start of the alarm cannot possible start the vehicle, if the hidden manual cut-off switch (to fuel pump, or whatever) is NOT in the 'ON' position.With my circuit (I hope, if it works), it would allow the remote start to start the truck. However, if a thief got in and crossed the wires to start the truck (connecting the ignition, like inserting a key and turning to the 'ON' position), then the vehicle would shut off. The only way to start the vehicle with this circuit, is by waving a magnet and holding it near the hall-effect sensor, activating the circuit and allowing power to flow through the relay and keep the truck running. Basically latching the relay, until the ignition (or key turned to a position other than the 'ON' position) is turned off and thus resetting the circuit for protection.The hall effect sensor would be hidden behind the dash somewhere, hidden. Only the installer would know where it was, and what triggers it, in this case, the South Pole of a Magnet.In my case, this will restrict the flow of power to the coil of the relay that allows power to go to the FICM (Fuel Injection Control Module) of my diesel truck. Without that FICM operating, the truck will crank over, but will not start. My hopes is that the thief will get tired of trying to figure out why it won't start, and just move on. With today's alarms, they come with a Starter Relay that cuts off the starter, well, that's a dead giveaway when the truck won't crank, and the thief knows this and easily bypasses it. My circuit, he'll spend awhile, (and perhaps never figuring it out), trying to figure out why the truck won't start. I suspect after a few minutes, he'll just get pissed and wonder off to the next vehicle. Leaving me my truck, and a Broken window and ignition to fix. Better then filing an insurance claim for a stolen vehicle. This, plus the fact of my battery operated additional siren, I don't think He'll stick around long.You will have to program the alarm so that if the doors are opened, then the remote start shuts off, resetting the circuit. If it doesn't shut off, then simple pulling wires from under the dash and connecting the ignition for the 'ON' position, will allow a thief to just driveaway. I may redesign this in the future, so it resets the circuit once the doors are open by having an input for the door pins.Keeping fingers crossed that it works. It works in simulation, but actually prototyping it is another story.One more thing, this circuit will work with a negative or a positive input from the alarm, by just switching a few jumpers. No need to use a bunch of relays to switch that around if need be. I've had to do that a few times with some alarm accessories, it will be nice not to have to with this.Enjoy the pic....

author: brainwash
author_rank: Frequent Contributor
timestamp: November 18, 2017, 05:08:54 am
content: I don't think injectors will try to fire without fuel, there are several pressure sensors that the ECU reads. Even if it did damage the injectors, it's cheaper than replacing the whole truck, in that unlikely scenario. It also proves theft and you can seek damages.Messing with any sensor (MAF, pressure, crank, gearbox, etc) will cause the truck to go into limp mode, so that could also be a possibility.Any method can be defeated with enough time and knowledge.

author: floobydust
author_rank: Super Contributor
timestamp: November 18, 2017, 05:22:01 am
content: I couldn't follow all of it - not sure the best way to disable the vehicle, I'll ask my diesel buddiesI find road vibration, potholes can jostle relays and maybe unlatch ? You don't want your truck to stall!

author: Falcon69
author_rank: Super Contributor
timestamp: November 18, 2017, 05:50:23 am
content: you can't disable fuel pump on diesel.having injectors fire without fuel to lubricate them, destroys them. Those injectors are $260 each, and that's just parts, labor is probably another $1500 to tear the engine down to replace them. You have to dismantle quite abit to get to them. From my understanding, Fuel Injectors on a diesel operate from pressure, NOT spark, unlike gasoline engines.Stopping the injectors from firing won't do anything to them. The fuel still tries to pump through them, but the injectors stop the fuel from continuing on to the engine. the fuel pump will cut itself off, as the truck isn't using any.This is what I've read on the subject from the Diesel Forums.

author: Falcon69
author_rank: Super Contributor
timestamp: November 18, 2017, 05:53:39 am
content: concerning the relays 'jostle' themselve on/off from potholes/bumps. unlikely. The FICM is already controlled by a 70amp relay. I am only interrupting the coil part of it, to prevent that relay from operating.The easiest and best way to safe guard your diesel, is put in a non-working relay for the FICM. It would take a thief hours to track down the problem. If you just take the relay out (which is a pain, popping the hood each time to access the fuse box), whose to say the thief doesn't just so happen to have one of those relays in his pocket to put in? Off he drives with your truck.But, I'm hoping this circuit does it all for me.

author: Ian.M
author_rank: Super Contributor
timestamp: November 18, 2017, 09:00:02 am
content: Add an extra oil pressure switch that when its on, forces your circuit to activate FICM relay coil power. That way, there's no way the circuit can loose state and shut down the FICM if the engine is already running (short of failure of the coil control relay, the new oil switch, or the new wiring). You'll probably need an adapter manifold to connect the extra switch +existing switch or sender to the same tapped hole in the block.

author: Falcon69
author_rank: Super Contributor
timestamp: November 19, 2017, 07:14:48 am
content: Not a bad idea Ian, but I'll have to think on how that will work.I'll have to redesign the circuit somehow to implement both the door switch and the oil pressure sensor.I think I can do it by adjusting my 3input XOR gate I have in the circuit, and upgrading it to an 8-input. That will give me the additional lines needed to keep the relays activated. Right now the XOR gate is allowing the Hall Sensor and the Alarm input (from remote start) to activate the relay.I'll play around with it and see if it works.

author: Falcon69
author_rank: Super Contributor
timestamp: November 19, 2017, 08:31:31 am
content: hey Ian, I thought about this....Since it will still require a relay between the factory power fuse and the coil of the factory FICM control relay to activate the FICM control for the oil pressure sensor, I'm in the same boat as I was before. If the relay fails, well, engine shuts off. So the oil pressure sensor is kinda a moot point.I did figure out the door open thing. That's an easy fix, and I can actually still use the boards I made up to do it. But, I think the alarm has that feature on it. I won't know until I hook it up or talk to an installer who has wired up this specific alarm.I also thought about putting a delay on all this. That way, the thief gets in, starts the truck and drives off, get's about a block down the street, truck shuts off. Then, if he gets caught, it's a GRAND THEFT AUTO charge, instead of just vandalism and maybe theft of items in the vehicle.

author: Mjolinor
author_rank: Frequent Contributor
timestamp: November 19, 2017, 08:56:52 am
content: I am pretty sure the injectors will not fire without fuel pressure.Is this a common rail engine? If it is then certainly the injectors will not fire. If it is not common rail then the injectors cannot fire as they need fuel pressure to fire.It is not a good idea to do this with 12 volt relays, on starting latched relays will likely drop out due to the volt drop across the battery.Whatever you do it is likely that you will get fault codes logged unless you put significant thought into this. Disabling the injectors directly is probably the best way but you will need to fit an emulator or it will log faults and may go into safe mode. This is not trivial as they are (depending on type) fed about 80 volts to fire. It is simplest to disable the starter motor. The advantage of this method is that your starter will not burn out trying to start it. Modern cars have a very small starter and they cannot put up with much non-starting before they throw their hand in.

author: Falcon69
author_rank: Super Contributor
timestamp: November 19, 2017, 09:31:05 am
content: They are 12volt relays. But they are not latched relays. I am using 3 relays to accomplish a latching mechanismIve seen this method done before on a starter for a vehicle using 12 volt relays. They still activate just fine. Voltage from battery ranges about 11 volts up to 14.4 volts. Sometimes voltage goes to 16 volts on some vehicles. Because this truck is diesel and requires a large starter and 2 batteries for the cranking amps, i don't see much of a voltage drop, if any, below 11 volts.It has been raining here and i have no garage. When it stops raining and i get time, i'll try and hook it up. I won't have the alarm in or remote start yet, but i can at least hook it up and see if it interrupts the FICM and truck not start with ignition. Then i can trigger the hall sensor and see if i can start it. If it does....and no magic smoke anywhere, i should be good to go.I've read from other forums, mainly the ford diesel forums, of people putting a manual toggle switch on that ficm relay coil and they have had no problems with injectors or the ficm.The only thing i am worried about is the relays in my circuit latching properly.

author: Mjolinor
author_rank: Frequent Contributor
timestamp: November 19, 2017, 11:26:31 am
content: If you put a scope on it you will see the volts drop to around 9 volts and that is usually enough to unlatch any latched relays be they latching relays or relays wired to latch as yours are. Proper latching relays are less likely to drop out as they are designed not to.Suck it and see is all you can do anyway, if it works then all is good but I reckon that 12 months down the line when your batteries are not as good as they were it will start failing. If you are getting 16 volts then you have a problem somewhere in the electrics.

author: Falcon69
author_rank: Super Contributor
timestamp: November 19, 2017, 09:55:36 pm
content: i understand what you are saying.I don't have 16 volts. I was just saying i have seen some cars where the battery is putting out that much, rather the alternator charging the battery was, which made it look like the battery had 16volts when engine running. So ya, something was wrong there.Most of the time my battery ranges between 11volts and 14.4 volts.If it doesn't work, I'll look for a different solution.

author: Falcon69
author_rank: Super Contributor
timestamp: December 18, 2017, 02:01:40 am
content: Sorry for the long delay. I've been busy with other projects (building a deck for mom, foot surgery, etc.).Today I managed to test the circuit. The one with two of the Optocouplers (Mosfet Optocouplers) worked flawlessly, switching on an LED from the relay that will be controlling the factory relay controlling power to the FICM of the truck. It turned on when either the alarm wire, or the hall sensor was triggered, went off when removed. It activated the relay when either the alarm or hall sensor wires were touched, then ignition wire was touched, the other relay latched, the alarm/hall sensor wire was removed, and the circuit stayed on, only to turn off when ignition wire removed (simulating the key turning from the 'ON' position of the ignition to the 'OFF' position. I just wish the relays didn't click. Hearing it, may persuade a thief to look for the problem and disconnect it all and reconnect to allow truck to start. I designed the circuit to work with either a positive or a negative input control from the alarm. The Hall sensor works perfect as well, now to test later to see if it will pick up the magnet from behind the dash. I don't see why not. It picks up the magnet from the other side of 3/16" tempered glassThe circuit I made with one Optocoupler and a Mosfet (not an optocoupler), made the circuit stay on, regardless of the input from ignition or alarm wire. I'm not sure what's going on there (I made this circuit because mosfet was cheaper than optocoupler). Before I could figure what was going on, or trace down the problem, I fried the mosfet. I forgot to switch the jumpers for the alarms input (NEG vs. POS), and put voltage to the alarm input wire. It fried the mosfet, magic smoke, DOH!But the other circuit works just fine, so I'm not going to worry about that one. Now to find the time to install the Alarm, and this circuit and put it to test in the real world environment.

author: perieanuo
author_rank: Frequent Contributor
timestamp: December 18, 2017, 05:52:58 pm
content: Best solution is a simple switch hidden really wellEnvoyé de mon HUAWEI NXT-L29 en utilisant Tapatalk

author: Falcon69
author_rank: Super Contributor
timestamp: December 18, 2017, 06:10:53 pm
content: A simple switch works well, but, what do you do when the Remote Start feature of the alarm tries to start, and that 'simple switch' is in the off position? No injectors will fire (or fuel, if hooked to fuel pump).No, a simple switch does not work in this situation. Did you read the entire thread to know what is going on? Or did you just read the title and respond?This circuit has a hall effect switch, so there is no moving parts and people won't know what it is or how to activate it, even if they do find it hidden behind the dash panel. Usually these kind of thieves are not very smart, otherwise they would have some other career, most likely a legit one.