car alarm w/ keypad keyless entry
Printed From: the12volt.com
Forum Name: Car Security and Convenience
Forum Discription: Car Alarms, Keyless Entries, Remote Starters, Immobilizer Bypasses, Sensors, Door Locks, Window Modules, Heated Mirrors, Heated Seats, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=103342
Printed Date: July 15, 2025 at 2:57 PM
Topic: car alarm w/ keypad keyless entry
Posted By: jasonlipka
Subject: car alarm w/ keypad keyless entry
Date Posted: March 23, 2008 at 6:17 PM
Hello to all, I am having a bit of a conundrum that I was hoping you guys with more experience might be able to help me with. I have a 1978 Ford F250 that I am rebuilding from the ground up. I am adding a whole mess of convenience features, one of them being a new Viper 5701 Responder LE (nice) car alarm/remote starter system on my vehicle. The vehicle has already been outfitted with a power door lock kit and something I thought would be especially "cool" on this particular vintage truck - keypad keyless entry (Made by Essex). Enter 'the problem'. The keypad system itself is pretty simple. Type in your code, it sends out a ground pulse to unlock. Hit 555 or 557 or 559 and the system sends out a lock pulse. The quandry: Say the Viper system was armed. You just wanted to run out to the truck real quick to grab something out of it but you left your Viper fob in the house. No prob - that's what you have the keypad for. So you type in your code, the truck unlocks, you open the door and - BOOM, full alarm trigger from the Viper. The problem is, as you probably already know, that the keypad system merely unlocked the doors. It did nothing in the way of disarming the Viper. This situation is similar to if someone used a slim jim to unlock your door. So my question: Any ideas how to integrate or interface the systems? I know that these Viper systems have an input that allows you to remote start, but I haven't seen anything about an input that allows you to arm/disarm the system via a wire. The arming I could live without - I'd just enable passive arming on the Viper. That way I could keypad in, do my business, shut the door, and the system would auto arm 30 secs later. I've contemplated several solutions. One was to set the keypad system up (I'm pretty good with wiring) such that upon unlocking via keypad and opening the door, it sends out a pulse on the valet/override line that would manually disarm. I was hoping for a little more seamless integration than that. I've also thought of some sort of signal repeater that acts as a code grabber. To clarify, you would program the key fob signal into this "box/module" for arm/disarm, and enable with the lock/unlock pulses from the keypad. You type in your code, the pulse goes to this box (enabling it), it sends out the signal to disarm/unlock. To my knowledge, no such box exists. Anyone know if there is something like that? So I was wondering if anybody had any other ideas. And before you suggest it, I'd rather NOT just set up the system to cut power to the viper system upon keypad unlock. I'd like it to actually disarm so if I needed to actually start the vehicle after keypadding in, it's still possible. Hope you guys can help! And thanks in advance! -Jason
Replies:
Posted By: Chris Luongo
Date Posted: March 23, 2008 at 6:40 PM
The Viper (or pretty much any aftermarket alarm) needs more than just the valet button pushed. It needs to see ignition and valet, in a certain sequence.
Look at your owner's manual about how to disarm the system using the valet button, and see if that's something you can duplicate. I know you said that's not what you wanted to to, but you might need to.
Another option would be to get a second remote for the Viper, attach wires to its circuit board, and use your keypad system to close the contacts for the "unlock" button on the remote.
If you wanted to get really fancy, you could hook up arm in this fashion too, and maybe even get the exterior keypad to activate the remote start.
One more idea.
Get a timer relay (DEI 528T, PAC TR-7). Have your keypad system trigger the timer relay. Have the timer relay break the Viper's door trigger input for a fixed amount of time.
You'll then have that amount of time to go into the truck and get your things. If you linger, the alarm will trigger.
You could just have an ordinary relay "latch" and interrupt the door trigger for an infinite amount of time, but if you don't somehow unlatch it afterward, it will eventually drain the battery.
Also, if your shock sensor is sensitive, you'll have to use the timer relay to interrupt that, too.
Posted By: jasonlipka
Date Posted: March 23, 2008 at 7:00 PM
I think the wiring a remote is the best option there. How would one go about doing that. I would have no idea what to do. So do I use a relay grounded by the keypad unlock to close the circuit that is closed when you hit the unlock button? What's the cleanest way to do this? Thanks, I didn't even think about that but then again I wasn't thinking about soldering on internals.
Posted By: jasonlipka
Date Posted: March 23, 2008 at 7:05 PM
Oh, and wiring up the keypad to arm would be exactly the same thing. And adding remote start isn't difficult at all. The keypad keyless entry has three auxilliary outputs. Once the correct unlock code is entered, you can press the 1/2 key, the 3/4 key, or the 7/8 key (5/6 is reserved for programming and lock codes) and the respective output is triggered. So it wouldn't be too hard to just type in my code and then hit, say, 1/2 and the truck would be starting as I climb into it. It would only save you a second or two but, hell, it would be cool.
Posted By: dualsport
Date Posted: March 23, 2008 at 9:33 PM
If you're sure there's no way to hardwire into the system to disarm it, which would be a better way to go, the idea for wiring into a sacrificial remote would be pretty easy, even if a bit convoluted.
You should be able to just tack on a couple of wires connected to the button contact points, and run them to a transistor switch driven by your keypad circuit. If the remote uses separate buttons for arm and disarm, you'd just connect another pair for the other button.
The type of transistor you need would depend on whether your keypad outputs are (+) or (-) polarity switched. When the transistor gets the signal from the keypad, it'd effectively close the connection between the remote button contacts. A ten cent transistor would do, since the switching current is so small.
Posted By: Chris Luongo
Date Posted: March 24, 2008 at 6:57 AM
I agree with dualsport, although we installers usually have easier access to relays than transistors. But the concept is the same.
I've done this only once, on a factory remote for a Jeep Grand Cherokee, because there wasn't a doorlock module available for it. Every brand of remote is going to be a little different.
Open up the remote. Generally, you'll see one of two things:
A. The circuit board of the remote has a micro pushbutton switch that is not seen by the user, with a rubber or plastic piece on the case.....when you push the plastic button on the outside, the micro switch gets pressed, completing the circuit.
B. A flat circuit board with what look like little interlaced "fingers." Imagine the tines of two forks slid into each other, end to end, without touching.
The remote's case has a rubber button, and on the backside of the button is black, conductive material. When the user presses the button down, it shorts the two sets of "fingers" together, completing the circuit.
In either case, it's just simply two traces on the circuit board, that when they touch together, the circuit is completed and the car unlocks.
Your main challenge is to figure out how to attach two small wires to those two traces on the circuit board.
On that Grand Cherokee, I drilled two tiny holes, one next to each trace on the board. The traces are usually covered something to insulate them. (Imagine clearcoat paint, but I'm sure it's fancier than that.) I scraped off a little of that "paint," being careful not to gouge the trace on the board.
Then I poked two small wires through the holes from behind, folded them down on the circuit board trace, and soldered.
So now, you'll have two wires dangling there, and if you touch them together, the car should unlock.
From there it's easy to wire a relay like this:
85: fused constant
86: negative signal from your keypad system
87: one of the wires from the remote
87a: not used
30: other wire from the remote
When 86 sees a ground, it shorts 87 and 30 together, which is what the remote wants to see.
P.S. Keep the remote in a semi-accessible place, because in a few years, you'll probably have to go back in there and replace its battery.
If it's a 12-volt remote, you could attach wires to its battery terminals, and wire it into constant power on the car.
If it has small button cells, usually 3 or 6 volts, you could get a small power supply (maybe a 5V cigarette adapter for a satellite radio), and use that to power the remote. However, if this Bronco isn't going to be driven every day, the little power supply might drain your battery over time.
Posted By: jasonlipka
Date Posted: March 24, 2008 at 8:00 AM
Wow guys, thanks for all the help! I really didn't think I would see a reply so fast. It's looking like the sacrificial remote is going to have to be the way. I called Viper and after a couple of minutes of convincing them that I just wanted to know so I could decide whether or not I want to buy it (tech support won't give you the time of day if they think you're going to install it yourself), they reluctantly admitted that there is no provision to hardwire an arm or disarm input into the system. In fact, they recommended that I just scrap the keypad idea. Imagine the nerve. Even so, I pondered that for a split second and decided that if I hadn't already drilled the holes for mounting, I might do it. I too thought about wiring up a small power supply. I realize that the battery inside the sacrificial transmitter would probably last a long time given it's very rare use, but I'm sure the one time I locked my keys in the car would be the time the battery dies. Well, I'll let you guys know how it goes. Thanks a lot.!
Posted By: dualsport
Date Posted: March 24, 2008 at 8:47 AM
I only figured using a transistor would be a safe way to go in case the keypad output didn't have enough drive for the relay. Most likely it does, though, if it's got those extra aux outputs.
Might want to use a diode on the relay coil to clamp the turn off voltage spike just in case.
If your remote uses something other than 12V, you could try using a relay to switch power to a resistor divider that drops the vehicle 12V to the required voltage. It'd only close when the keypad is outputting, so no draw on standby. The remote uses so little current you shoud be able to get away with this. Just use lower resistances (and higher power ratings) as needed to power the remote without the voltage dropping further from the draw of the remote.
I'd just use the battery for simplicity and just replace it yearly. I assume the keypad output pulse duration is determined by how long the button is pressed rather than some fixed time; if not, the battery might get used up faster.
Posted By: jasonlipka
Date Posted: March 24, 2008 at 12:00 PM
All the outputs, including the lock and unlock, are 250mA grounding outputs. It's pretty obvious they were designed to power an external relay. The remote uses a CR2032 3V battery. I've done some checking and found various DC/DC Converters that would satisfy the application for around $20. I don't know what one of these converters consume on standby but it can't be much. It's pretty much a daily driver but I would like to be able to leave it unattended on business trips or vacations in the airport parking lot without having to worry about coming home to a dead battery. In case you haven't noticed throughout the thread, I like to keep my options open. I'm not really following on the resistor system you are talking about dualsport. I would like to make it so power is only being consumed during system operation but I don't really know about wiring a whole bunch of resistors and stuff like that into the system. I'd like it to look nice, too, rather than having a loose PC board dangling beneath my dash. Any thoughts on improving the system's aesthetics are more than welcome here too. Once again, I'd just like to say thanks, you guys have been awesome in helping me with this snag.
Posted By: dualsport
Date Posted: March 24, 2008 at 12:23 PM
That'd be an advantage of using transistors to switch your remote, three transistors to handle arm, disarm, and remote start would be smaller than a standard sized relay. The relays are easier to work with because they're larger and more forgiving, so you can decide which is more important. If you're ready to solder onto the remote, you should be comfortable enough to connect up some transistors. If you don't have a good soldering iron for the work, you should find someone that could do it for you or get one; wouldn't want to risk damaging an expensive remote.
The resistor divider I mentioned would just be two resistors connected together in series.
Then when you supply 12V to one end and ground at another, you should get a lower voltage at the middle to use for powering the remote. By the selection of the right resistor values, you can get the 3V you need from the 12V input. The reason this isn't usually used is because it's not regulated, so drawing power from the middle affects the voltage division, with the output voltage dropping. But because the remote draws so little you can get away with it.
But I agree it's really not worth the trouble when the battery will last years anyway; just put it somewhere accessible so you can change it every now and then, as Chris said.
Posted By: jasonlipka
Date Posted: March 24, 2008 at 12:42 PM
Yeah I'll probably just leave out the power supply and let the battery provide the power. I do however like the Transistor idea. With all the crap I've added, underdash real estate is becoming an ever-diminishing commodity. Not to mention the fact this vehicle should be sponsored by Bosch with all the f-in relays it has on it. I am nowhere near familiar with transistors like I am with relays. In fact, besides my circuits and mechatronics classes I took in college, I've never used one. So for the wiring on the disarm/unlock, will I hook one side of the unlook button to the collector, the other side to the emitter, and the keypad unlock pulse wire to the base? I did some browsing at Radio Shack but I have no idea what to get. I know they classify them by P-N-P and so on but I don't know which one to get. I vaguely remember our discussion about transistors and diodes in a material properties class and know that this has something to do with the flow direction of the electrons, but I don't know which one I need. Maybe someone could submit a part number? One last thing. What do you think would be the cleanest way to wire this up? By that, I mean like is there some sort of mini bread board or some sort of small enclosure that I could stuff all this wiring in rather than just having 3 transistors dangling under dash? Thanks a ton guys.
Posted By: dualsport
Date Posted: March 24, 2008 at 3:44 PM
You might try this, using a general purpose PNP transistor-
This would be done for each of the functions like arm, disarm, RS, but try it on one first to see if it works out. The resistor value isn't be too critical, so you can experiment with what you have handy. Just don't go too low to minimize the stress on the transistor. If it's too high it just won't work, but shouldn't harm anything.
The transistors are about 4 cents each from mouser.com if you can't find any locally. linky
If you can find some perfboard, connect up the bits with pin sockets for the transistors, so it can be plugged in for installation or easy replacement. You could make a connector with a Molex connector so it can be unplugged if necessary.
Important thing is to measure the polarity of the button contacts to see which one is positive. And verify first that it transmits as you expect when you short the contacts together before going forward with anything else.
Posted By: jasonlipka
Date Posted: April 09, 2008 at 9:57 AM
So now I found out that most Compustar units come with 2 programmable inputs tha can be used for this. Unfortunately, while this problem is solved, another is created. I also have an electric retracting tonneau cover that I was going to wire up to be programmed by the auxilliary channels. Compustar units do not allow the aux outputs to be used in "validity" mode. Validity mode is where the aux output is active for as long as the button is pressed, which is ideal for my tonno. Compustar only allows timed and pulse. I know some of you will say "Well just use the timed!" That doesn't really suit me because I'd like to be able to stop the tonno wherever I want, whether that is 1/4 open, 1/2 open, etc. The other problem with timed is that there is such a temp variation here in Wyoming that on a summer day, it might only take 15 secs to open, but on a cold winter day, it could take double (or more) the time. Therefore, I think I'm still at the point where I am gonna use the Viper and sacrifice a remote. The outputs are more flexible and the buttons on it are actually intuitive, rather than Compustar's I, II, III, & IV. The other thing I like is the Viper remote was specifically designed to be used with one hand (no two buttons pressed at the same time). While this creates more sequences to remember, if you come out of the grocery store with your hands full, you can pop the trunk (or in my case, retract the tonno) without fumbling with your groceries. So I'll let you guys know how it turns out.
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