1988GTA500HP

I came across this article at Autospeed on building your own DIY Immobiliser.

http://www.autospeed.com/A_107975/cms/article.html

It seems pretty slick so I decided to build one for my son's car. After gathering all the parts, mostly from Radio Shack, I had trouble wiring it because I didn't understand all the electrical symbols in the schematic. Through trial and error, I did, however, get it to work. In order to save anyone else from having to use the trial and error method, I redrew the schematic with the Radio Shack part numbers in parenthesis and the pin numbers used for the connections. So far I have just bench tested it but it worked as advertised. I will be installing it in his car shortly. I will be happy to post some pictures of the parts or from the bench test if anyone wishes to see them.

Enjoy.

1988GTA500HP

More pics.

1988GTA500HP

I had an old reed switch in an alarm contact I had purchased from Radio Shack years ago. They no longer sell alarm contacts separately. I found the battery operated alarm in the third picture at Harbor Freight. It was only 89 cents. I opened it up and sure enough it has a magnetic reed switch in it.

1988GTA500HP

A close up of the reed switch. It looks like a thin glass tube. Since the leads are so short I decided to just cut the circuit board and leave enough room to solder the wires onto the back of it. I also used a socket from Radio Shack to mount the DPDT relay in so I can replace it if it ever fails. I made all my connections to the socket and then mounted the whole thing in a case I had laying around to protect the resistor and the jumpers from shorting out. This whole thing will be hung unders the dash somewhere.

Pocket

iTrader: (24)

Cool thread

1988GTA500HP

Thanks, Pocket. I had visions of someone asking me to post some pictures 3 months from now. I probably wouldn't remember everything so I thought I would just post them now.

Not being one to waste anything, I decided to mount the reed switch in the magnetic side of the door alarm. A small screwdriver made prying out the back of the magnet holder simple. I will probably use the magnet I found inside to trigger the immobiliser. I'll see if it is strong enough after I mount the reed switch behind the interior of the car. I used a rat file to create two openings for the wires and a quick set epoxy to hold everthing together. I was careful to make sure the switch was mounted the same direction as it was in the alarm.

The second picture is the flashing LED in a socket all soldered with heat shrink tubing to protect the contacts.

The third picture is the momentary switch all ready for installation as well.

1988GTA500HP

Not being one to just drill holes in a 22 year old dashboard, even on a car that doesn't have a matching engine, I found a panel on the dash with just a cover on it. I'm sure it covered where some buttons would be if a certain options came with the car. I used that panel to mount the switch and the blinking LED.

I also noticed in the bench test that if I similated disconnecting the battery by turning off my power converter, when I turn the converter back on the car is in the disabled mode with the LED flashing. This is great for theft prevention but wouldn't be so hot when having the car serviced. If the shop disconnected the battery for any reason the car wouldn't start after they reconnect the battery. I don't want to tell the mechanic how to trigger the magnetic reed switch, because that is kind of defeating the whole purpose of all my work. So I built in a bypass function for just such occasions. I simply added a 2 into 1 terminal connector on pin 30 of the heavy duty relay. It's in the back when the relay is mounted and you can't see it. So if my son needs to take the car to the shop for any reason he can just unplug the connector from pin 87 and add it to pin 30, bypassing the entire relay.

1988GTA500HP

Well I installed the system into his car today with the exception of actually cutting into a line in the engine compartment to disable the car. I wanted to make sure everything worked before I did that. I used epoxy again to attach the reed switch to the backside of the interior panel. I'm am not going to reveal which panel it is behind, but I used a spring clamp to hold it in place until it dried.

To make sure everything was working, what i did was connect a continuity tester to pins 87 and 30 of the heavy duty automotive relay and stood the multitester on end so I could see it from the passenger compartment. I observed it said OL for open line, as I expected. I then swiped the magnet by the hidden reed switch and the meter showed zero resistance....perfect. I then hit the pushbutton and the LED started flashing again and the meter went back to open line. I was surpised on how sensitive the reed switch is even through the interior panel it is mounted behind. I held the magnet about 1/2" away from the panel and swiped by at a pretty reasonable pace and it tripped the reed switch without a problem. It does have to go directly over the reed switch however, so make sure you plan accordingly. The LED is bright enough to see easily from outside the car, a deterent in itself. It flashes about once per second. The 330 Ohm resistor was used because I couldn't find a 12 volt LED at Radio Shack. I read a while back that in order to reduce current to the LED, you should take the supply voltage (12v) minus the LED voltage (3v) divided by the LED amperage (.035). If your input voltage is different, you may need a different resistor. You should round UP from you calculated resistence to an available resistor.

When choosing a mounting point for the pushbutton switch, make sure you put it somewhere where you won't accidently press it while driving, as this will disable the car.

This is what the finished product looks like. So tomorrow I'm off to Radio Shack again to get an inline fuse holder, which I forgot, and then I will actually cut into the line to disable the car.

1988GTA500HP

Well everything is done and it works great. The first picture is the DPDT relay mounted under the dash and the second picture is the heavy duty automotive relay mounted under the hood. As a side note, the ceramic magnets from Radio Shack are not strong enough to trip the reed switch. You will need stronger magnets or use the one from the Harbor Freight door alarm, it works fine.

Yahtzee

Which circuit on the car are you planning on tying into? I would think either the fuel pump relay or maybe the distributor +12vdc circuit would work. This is a really cool thread, I just might have to do this and maybe prevent myself from having to buy an alarm. I have had a third gen stolen before and they just broke my steering column and used a screw driver to slide the ignition actuator switch. I hate thieves.

1988GTA500HP

Hi TT84Z5SPD. Either of those circuits would work. I prefer not to reveal online which circuit I used. If you want to test it beforehand, just disconnect the circuit you are considering and try starting the car. That is what I did. Altogether it was about 10 hours of work and cost between $30 and $35 to complete. I could have done it cheaper by not using a relay socket or bought the magnets. I also could have done it quicker but I did some other things to the dash while it was apart, and of course I kept taking pictures. Make sure you bench test everything and test everything again when the system is installed but before you cut into your circuit. Good luck.

Edit: This system should prevent them from getting your car but they probably would still destroy your column. Of course, any car could just be towed away.

NINÅ

“……..any car could just be towed away.”

That’s ok, there’s GPS.

Heh Heh Heh Heh Heh Heh

◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙
Happy Racing!

Pocket

iTrader: (24)

Running the entire engine IGN system to a relay and putting the immobilizer on that would be a very easy for sure kill for both carb and EFI

1988GTA500HP

As the original article on Autospeed states, "open-circuiting the ignition key starting signal to the starter motor solenoid...the car can still be jump started". Also it states "If your car has an electric fuel pump, the immobiliser can disable this. However, note that both EFI and carby cars will still start and run a short period even with the fuel pump stopped. This might be just enough time for the thief to drive to the middle of the nearest major road intersection before the car dies". Please read the original article that I supplied a link to in the first posting as this thread is really just a supplement to that.

Again I advise, disable the circuit you wish to kill and try starting the car before you make your decision.

Pocket

iTrader: (24)

Run multiple relays, all called by a common wire, IE ground side. That way you can disable everything individually from a single relay point

1988GTA500HP

That would definitely disable everything, Pocket. An interesting approach.

1988GTA500HP

Update: I placed the magnet in a key fob and it has been working absolutely great. You could be sitting next to me in the passenger seat and never figure out how I shut the immobiliser off. I highly recommend this mod.

chads89ta

iTrader: (6)

just cut the power wire to the distributor or coil, it may still crank over but no spark

1988GTA500HP

Exactly, chads89ta, that's the easiest and most common approach.

ebaum744

Hook up the relays to the coil and distributor like previously mentioned, but for the "activation" button, use a normally open pushbutton, and install it in the drivers side door, like the courtesy lights, it'll only activate the system when the door opens once... That way you don't have to worry about remembering to re-activate the system when the vehicle is shut off, so when the driver exits the vehicle, the immoblizer reactivates itself so to speak.

1988GTA500HP

The only problem I can see with that, ebaum, would be if you ever open the door while the car is running it would kill the engine. I'm not sure that would be desirable. But if you don't mind that, then it would be pretty slick.

92RS_Ttop

iTrader: (3)

This is a great idea, and I'll be doing this to my Camaro as soon as I finish up the exhaust and Keyless Entry project I have going on right now. I do have a couple questions though.

When you turn the car off with the key, does that automatically re-arm the system, or do you have to manually press the button to re-arm it?

When you turn the key off, I assume the engine shuts off normally?

I want to make this as wife-proof as possible so she doesn't accidentally screw something up if I need to let her take it somewhere.

1988GTA500HP

Good luck.

92RS_Ttop

iTrader: (3)

Actually, I was going to try and wire it so it re-arms automatically after you turn the key off. That's if I even keep the key cause I've been kicking around some ideas about removing the key altogether and using another method to turn the ignition on.

I can make sure she doesn't press a button while driving, all I have to do is put it somewhere she can't reach it easily.

Thanks for the answers. If you don't mind, once I get it worked out so the system re-arms automatically when the key is turned off I'll post up the diagram in case anyone else wants to make that change.

1988GTA500HP

I don't mind at all Ttop. I think everyone's ideas should be added to the thread. It gives people more choices. You do realise that if it arms automatically that you will have to show everyone that uses the car how to disarm it and give them the key fob, like mechanics, valets, tow truck drivers, relatives, etc. unless you build in the bypass and are sure to use it when needed. You can't forget to disarm it with the flashing LED and the fact that the car won't start, but if the LED isn't flashing you need to remember to arm it. I never forget to arm it because very quickly I got in the habit of looking at the LED when entering and exiting the car.

92RS_Ttop

iTrader: (3)

I do realize the issues involved with having it automatically arm itself, and will definitely include the bypass in it in case I ever need it.

For me though, its not really an issue as I'm the only one that drives the car right now. My wife is still re-learning how to drive a stick as she hasn't done it in 12 years and the mechanic I take it to for inspections doesn't drive it. I pull it into the garage, he inspects it, and I drive it back out and leave.

I haven't decided what I'm going to do with the magnet yet. I have a small magnet from a computer hard drive that should be plenty powerful enough to trigger the reed switch. Its also small enough to hide in something thin like an SD card that I could leave laying in the ashtray all the time and not have to worry about losing it. I've had several key fobs fall off my keychains in the past.

My other thought on that was to see if I can put the magnet into my remote that I use to open the doors. I shaved the door handles on the Camaro and if I can add the magnet to it that would be perfect.

1988GTA500HP

That sounds great. If I can help you in any way, just post your questions. I think you will be very happy with the immobilser.

1988GTA500HP

You know. ttop, I've been thinking about what you want to do. If you noticed in my bench test the system activates itself if the power is disconnected and reconnected. You may be able to use that to your advantage but creating a momentary blip in the power feed triggered by your remote lock button or something like that.

92RS_Ttop

iTrader: (3)

I hadn't noticed that, no. Thanks, that helps a lot!

92RS_Ttop

iTrader: (3)

Ok, I FINALLY got it figured out. I was trying to do it by adding a single SPDT relay, but after 4 days of trying to make it work I've come to the conclusion that its just not possible. It can easily be done with 2 SPDT relays though. It uses the door switch as a trigger to rearm the system as was suggested by ebaum. Using only 1 relay, it will kill the car if its running which I don't want it to do. Adding a second relay however allows you to tap into a wire that is only "hot" when the car is running to prevent the door switch from killing the engine. I also added a bypass switch to the diagram in case anyone wants to see that as well. It functions completely separately from the relays that automatically re-arm the system. Wiring diagram posted below, yes its done with MS Paint

Comments, questions, suggestions, etc are welcome.

1988GTA500HP

Looks great, ttop. Is it just on paper so far or have you built a prototype? Does that setup mean you won't be able to start the car with the door open? Just wondering because you have gone far beyond my capabilities of understanding the schematic.

92RS_Ttop

iTrader: (3)

So far it is just on paper. I built and bench-tested the original circuit using an old computer power supply for my +12V, but the internal breaker in it kept tripping so it was a real PITA to test. Once I get that issue sorted out I'll be able to fully bench test this setup.

Honestly, starting the car with the door open hadn't crossed my mind. It should be possible as long as you turn the key "on" before swiping the magnet across the reed switch. Otherwise, the open door will prevent the DPDT relay from staying "on".

Hopefully Saturday night I can fully test the design. I'll make sure to try testing it with the "door" already open too.

1988GTA500HP

You would be surprised how many times you do something until you can't do it anymore. The circuit is def above my skill level but I just figured it might be an issue if using the door switch. I enjoy the bench testing part of it. You get to see it work but don't have to install anything.

92RS_Ttop

iTrader: (3)

Using the door switch is the only way I could think of to get around another problem. Any other method I could think of would require you to turn the key "On" before you swipe the magnet. I figured that would be a bit obvious to passengers, and cumbersome to do every time so I didn't want to do it that way.

1988GTA500HP

You could always use the door chime circuit. But then you would have to make sure you always open your door before pulling out the key. Not too much of a hassle.

92RS_Ttop

iTrader: (3)

I never thought of the door chime circuit. Probably cause I took the module out so I could run some wiring and never put it back in. That was 2 years ago

I tested the circuit I posted earlier and it works just fine. Car stays running if you open the door. Once the key is off, open the door and it re-arms itself.

1988GTA500HP

Did you simulate starting the car with the door open?

92RS_Ttop

iTrader: (3)

Oops! I knew I forgot something last night. I'll check it and post up the results.

92RS_Ttop

iTrader: (3)

I tried it tonight. If you try starting the car with the door open, the relay closes when you swipe the magnet over the reed switch but it doesn't stay "on" so you can't start the car. If you turn the key to the "On" position before you swipe the magnet then you can start the car normally. Once you turn the car off with the door open, it will immediately re-arm the system.

1988GTA500HP

Just as I suspected. Can your wife deal with that? If you have to turn the car on than you certainly wouldn't want the magnet attached to the key ring, way too obvious.

92RS_Ttop

iTrader: (3)

For as often as she will drive it, I don't think it will be a problem.

It's really too bad that the little button lock on my ignition cylinder appears to be mechanical and not electric as that would make a perfect button to re-arm the system since you have to push it to get the key out.

1988GTA500HP

Yeah it would. With your skills maybe you can turn it into a grounding button.

tjrq559

Hi, I noticed that there hasn't been any activity on this thread for about a year but I am going to ask anyway. I bought the items to do install this in my car, I got a 3PDT & Auto Relay made by NTE Inc. (part#'s R10-14D10-12N & R51-5D40-12F). I would like to know if these 2 items will work for this setup.

1988GTA500HP

Unfortunately I don't know enough about electronics to tell you if it will work. The relay I used was Double Pole Double Throw. A 3 pole like you have may work if it will still function as a 2 pole. If the relay is heavy duty I can't see why that wouldn't work. A relay is simply a device which allows you to control a lot of voltage using a small voltage as the trigger. That said, why didn't you just get the parts from Radio Shack?

92RS_Ttop

iTrader: (3)

According the spec sheets on those parts from that site they should work just fine. The 3PDT relay is a bit overkill as you only need 2 poles on it for this circuit.

tjrq559

Thank you for both of the replies.One more thing, could I not wire in a on/off switch in place of the reed switch?

92RS_Ttop

iTrader: (3)

Sure you could. Kinda takes some of the 'coolness' factor out of it though. Just make sure its a momentary switch, not an on/off type. You could really simplify the wiring with a regular on/off switch though if you wanted to use a normal switch.

Six_Shooter

iTrader: (2)

I know this system has long been installed, but I just wanted to mention that the LED holder that is used, is meant to have the LED installed from behind, not the front as pictured.

You pop out the rubber plug, insert the LED into the holder, and then slide the rubber plug back on. I will usually slip the wires through the plug and solder to the LED before actually re-assembling though, just so that the connections can be insulated by the rubber plug.

It is the concern of security and ease of use that I use immobilzers that are offered by manufactures that use transponders to disarm the circuit. They will passively re-arm every time the key is turned off, without fear of shutting the car down while driving. You also won't cause damage to credit cards or other devices, by having a magnet in your pocket.

yazen

Hello all, I would like to thank you for this post, its very helpful and useful to people like me. Appreciated it. I have few questions if I may ask:

1) I got this DPDT relay http://uk.farnell.com/finder/60-12-8...vac/dp/1169187 is it the correct one?
2) The coil in DPDT relay is on 2 and 7, but the diagram here shows 7 and 8, how it that possible?
3) Do I have to keep the magnet in contact with the reed switch all the time in order to keep the circuit up and running? Because the way I understand it is that, when I remove the magnet from the reed switch the circuit would die! Or am I missing something here.


Thank you all,
Yazen

1988GTA500HP

Hi Yazen. I'll help as much as I can since you have a different relay than I used. Since a relay simply allows you to control a higher voltage with lower voltage circuit, any automotive DPDT (Double Pole Double Throw) relay should work. The one you have says DPCO. I have no idea what the CO is, someone with more electronic knowledge might jump in here and help you. If you look at the picture in the first post which shows the relay, you will see that pins 85 and 86 are the coil circuit, and 87 and 30 are the pins controlling the car circuit you want to interrupt. You may be able to just use your corresponding pin numbers for your relay. You can test the entire circuit before even starting the install.

As far as the magnet, it only has to pass by or touch the reed switch. It does not need to stay in contact with the reed switch. The blinking LED will shut off when you have successfully tripped the reed switch.

Hope that helps.