2 Sensors for Alarm with 1 connector

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=53542
Printed Date: April 26, 2024 at 3:45 PM

Topic: 2 Sensors for Alarm with 1 connector

Posted By: vseth
Subject: 2 Sensors for Alarm with 1 connector
Date Posted: April 08, 2005 at 1:12 PM

Installing alarm/starter on my Toyota Corolla 1998 LE. The alarm unit has a 3-pin connector for an alarm sensor, i've got two type of sensors a shock sensor and a microwave/radar sensor, both with 3-pin connectors for the alarm. Since, i want to connect both of the units to the starter module, what would be the best way to do it. If I have to use diodes to isolate the two sensor circuits, I would appreciate a circuit diagram and the diode specs, if they are required. The three wires are:

red: alarms positive 12V output

black: ground

blue: trigger signal

Replies:

Posted By: Powermyster
Date Posted: April 08, 2005 at 4:09 PM

Posted By: vseth
Date Posted: April 08, 2005 at 6:48 PM

No need to isolate the power / ground wiring ?

Posted By: moshpitmickey
Date Posted: April 08, 2005 at 8:27 PM

No, no need to isolate power and ground. Excellent diagram powermyster.

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moshpitmickey

Posted By: vseth
Date Posted: May 11, 2005 at 2:15 PM

Some questions:

- Which side should the cathode of the diode be facing ? The diagram below for isolating door triggers shows the cathode towards the triggers, whereas the diagram above for isolating sensors shows the cathode towards the alarm.

- Do both triggers need to be isolated ? The diagram below shows diode isolation on both triggers, whereas the diagram above shows diode isolation only on one of the triggers.

- With a microwave, ultrasonic and shock sensor ( have 2 sensor trigger inputs in alarm, three sensor triggers ), which two would be a better choice to isolate within one circuit, and which should be connected by itself. Does it even make a difference ?

- I'm attaching here some comments provided by the vendor of the alarm, warning about possible shorts. Am I taking any risk with this diode isolation, as his feedback is not exactly clear, is he just referring to bad wire splice connections or something else? Here's his input on connecting multiple sensors:

"there is the way to connect the tripple senesor, but you must be very careful to make parallel connection . if you want to install two sensors in 1 input port: for example: since HT800D has only two sensor ports alarm, you need to connect them( two sensors) in parallel...

make sure please do not short the sensor port + and - during two sensors connection.

if you make it short the sensor port (+ and -) you will fry the alarm

there are three wires in the port (+ , - , trigger)

I just want to warn you, all alarms has been checked before it shipping it out, so,,, make sure do not blame us if you make a short circuit. please just becareful. ( it is not recoverable once you make the damage on sensor port)"

https://www.the12volt.com/diodes/diodes.asp

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Posted By: floaterr
Date Posted: May 13, 2005 at 3:18 AM

1- Believe your right about the diodes being backwards on the twin shock sensor setup.

2- Yes both triggers, however your sensor only has 1 trigger wire correct? So in your case wouldn't be able to install 2nd diode.
As for the door you have to think of it this way. You don't CUT the shock sensor trigger and put a diode inline AND another diode inline with the motion sensor. You just have to isolate 1 from the other. Doing so with both sensor trigger wires because the sensors are like 2 different cars. (kinda like a 4 door car but not exactly).

3- I'd put your ultra and microwave together. Only cause they basically detect the same thing; movement inside the vehicle.

EXAMPLE: (if you had an LCD alarm)

The shock sensor goes off and then next you see the motion/sonic went off. <- someone got inside most likely

Just the shock zone goes off. Could be someone bumped the car, bass from a car, etc... May not be neccicary to get the gun and go running.... naked... ;)

Posted By: vseth
Date Posted: May 13, 2005 at 8:02 AM

Question 2: "Do both triggers need to be isolated ? The diagram below shows diode isolation on both triggers, whereas the diagram above shows diode isolation only on one of the triggers."

With both triggers, I'm not referring to 2 triggers as in a dual-stage sensor, but the fact that I have two sensors with one trigger each. So if I put a diode only in one sensor's triggers ( as in the diagram above ), does that not leave open the trigger wire of the other sensor to a loopback when the diode-isolated trigger fires ( if that's even an issue ) ?

Posted By: vseth
Date Posted: May 13, 2005 at 8:23 AM

Also any input on the 4th item in the "Some Questions" post above ?