Write-Up: How To Wire Up A Dei Shock Sensor To The Oem Alarm

[crazykn]

The purpose of this write up is to add aDEI 504D shock sensor to the stock OEM Alarm system. Now that being said, this is a modification that you do at your own risk and that I am not liable for your actions pertaining to this modification.

This modification does require some basic electronic/electrical knowledge and soldering skills too.

The OEM alarm system for the S70 and 850 are pretty unique that they don't use a negative (ground) signal to trigger that alarm. The area where we will tap into the alarm is the hood release latch (driver side). This latch provides a ground to the alarm system when the hood is closed and the circuit is broken (no ground) when the hood is opened. That means that the the alarm triggers when the circuit is broken (ground is cut) when the hood is lifted and therefore triggers the alarm. The way that DEI 504D Shock sensor works (which is how many DEI sensors work) is it provides a ground when it triggers, which is kind of the opposite of how the OEM system works.

So in order to interface the DEI 504D module to the hood latch sensor, is to use a relay so that the relay will break the ground connection when the shock sensor gives its TRIGGER signal. This is essentially how it needs to be wired up:

So basically we tapped the hood latch alarm wires, but cutting into one of them and then attaching them to the relay that will be driven by the DEI 504D.

Now when you buy your relay, you CANNOT get any old relay. It must be a relay that has a coil current of 30mA or less (at 12V)! The reason behind this is that the DEI 504D cannot deliver more than 34/35mA of current to the relay. The standard Bosch relays take almost 120mA and the Volvo J relays take about 90mA which is much more than what the DEI module can provide. The easiest to obtain part is from radioshack and its a blue little relay. Its part number: 275-0248 and it is a SPDT Miniature Relay. It consumes about 30mA at 12V which is just enough to work. Do not throw away the packaging wrapper, it has the electrical diagram on it (as well as the pin assignments that I drew on the diagram above). You will have to solder wires to the small pins of this relay.

I went to the junkyard to cut me off some connectors (from the hood latch and its connectors) and made a simple adapter for the interface to the OEM wires. This isn't necessary to do, if you just cut into and rewire it directly.

Here are some close ups to the DEI 504D module. This module ideally should be tied to a wiring harness or something 'soft'. It isn't intended to be mounted to the frame of the car, but some experimentation on location will be needed to ensure a good result for your car.

On the end you should have something similar to this. This isn't completed, I will be installing this in my car tomorrow and will report the results. It works well on my bench and from testing so it should be working when placed in the car.

This isn't really a true writeup, but it will get you started on adding sensors to your OEM alarm system. As a bit of a note, the alarm may not be on all the time (when you drive or in the car), but the sensors will always have power at this point. So some sensors, like a Tilt/Motion sensor will require a ignition wire or other modification to work. Ultrasonic sensors will work well here too, and in theory glass breakage sensors as well.

Lastly, YOU MUST FUSE THE 12V supply for the DEI Module and the Relay!

[Oreo931]

Very cool! Let us know where/how you end up mounting it, I'm curious. Also, why did you not use the warn away function, and if you did want to use it, is it difficult to add on?

[crazykn]

I choose not to use the warn-away function wire (our OEM alarm doesn't do a warn-away chirp or anything like that), because it would probably make the shock sensor too sensitive. For example, even passing cars with booming subs could set it off. If you wanted to use the warn-away feature, you can just crimp and tie it together with the Trigger wire, and it will combine them to trigger the alarm.

I actually haven't mounted it yet. I finished the wiring tonight and about to put it in the car tomorrow.

Another cheap mod to make the alarm a bit louder is to use (or even take) a Volvo 850/x70 front horn and mount it in the place of the disc horn in the back firewall. The connector is EXACTLY the same.

[MyCarIsRed]

Nicely done.

Those ratshack blue relays are actually pretty durable; I've one running for about 8 years now and it's twice past it's cycle life.

You can get pins to fit it so you don't need to solder. Just grab one of their smaller DB15 connector packs and crimp the female pins onto a wire (like a spade connector). Little hot glue and done.

[crazykn]

Today I finally installed the shock sensor. It works great! Just as a warning, the relay will keep clicking, because the 12V+ is constantly on when any vibration occurs (even when driving). Its not noticible when driving though.

[BEJinFBK]

Today I finally installed the shock sensor. It works great! Just as a warning, the relay will keep clicking, because the 12V+ is constantly on when any vibration occurs (even when driving). Its not noticible when driving though.

A guy could add a relay that cuts power when the ignition is on...

BTW - Nice use of shrink tubing and +1 for fusing! ;)

[Chilled man]

you can make this for $$$ I has :D