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Adding Ground When Armed to Alpine 8030b - FYI

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Member - Posts: 1
Member spacespace
Joined: October 05, 2009
Location: Pennsylvania, United States
Posted: October 22, 2009 at 8:20 PM / IP Logged  
I've got one of these ancient alarms in my car, I've had it since 1992, and I decided to add a DEI tilt sensor and a Crimeguard proximity sensor to it. Both sensors require a ground-when-armed signal to work properly, which the 8030B doesn't have.
I'm not asking for help. I've figured it out, and hopefully the information will help someone else.
On the 8030B circuit board, there's a chip called 74HC109AP at the top center. It's a "Dual JK flip-flop with set and reset; positive-edge trigger" chip. Pin 9 is ~Q2 and gives a ground-when-armed output (conversely, pin 10 is Q2 and gives a 5V-when-armed output). You can use one of these pins as a basis for a ground-when-armed signal.
DO NOT use the pins directly for your signal. I found that the alarm's arming function is extremely sensitive to current draw, and if you draw too much, it won't arm. Besides, you really want to protect your alarm from any accidental shorts. You'll need to add a simple circuit to make the signal usable. The circuit itself is a lot easier to build than it is to squeeze in the alarm case.
The easiest way to tap the signal is to use pin 9 (~Q2), but not at the chip. You can get it by tapping the **cathode** of diode 39. D39 is about in-line with the JK flip-flop, but toward the opposite end of the alarm. Testing for continuity between the ~Q2 pin and D39 will tell you that you've got the right end.
I'm attaching a picture, but essentially I used the diode output to drive a PNP transistor, which switched on an NPN transistor. I use the collector of the NPN as the ground-when-armed signal.
I found that the alarm wouldn't arm properly unless the initial resistor was fairly large (22k in this case). I first tried a 4.7k resistor and the alarm didn't want to arm, but going to 22k fixed the problem.
The sensors seem to work with this setup. I'm a little concerned about the fact that the NPN isn't protected by a resistor, but I found that putting a small (10-ohm) resistor on the collector stopped the tilt sensor from working properly. It seemed to want a true ground.
Perhaps someone can come up with a better design, but this at least shows that it's possible. I don't know about other Alpine alarms (e.g. an 8040), but I imagine it's possible.
Unfortunately the 8030B doesn't support pre-warn, so I'm scratching my head to come up with a way to generate an un-obnoxious soft chirp from the proximity pre-warn output...but it can't be as hard as figuring this out was.
Adding Ground When Armed to Alpine 8030b - FYI -- posted image.

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