Adding an audio (glass break) sensor

[Vuk]

I am trying to integrate an aftermarket audio sensor into the factory alarm system on my 2016 Sierra 1500 AllTerrain, so I thought I would share my thoughts. I picked up a DEI (Directed Electronics) 506T audio sensor which seems to be working well. It detects key rattling almost instantly, and also responds to repetitive knocks on glass with metal (i.e., key, screwdriver). It's interface is simple: three wires; +12V, ground, signal output.

 

Problem 1. Looking after a place to integrate additional sensors I found that the simplest thing to do would be to emulate opening of the hood. The wiring for the hood switch is easily accessible, and the OEM alarm system reacts to the hood switch instantly when armed. Essentially, I would like to use the output of the audio sensor to drive a relay that will close the hood switch making knocking on the glass equivalent to opening the hood. The sensor appears to consume very little (<1mA), so there's no problem in having it run all the time. However, I wouldn't like the DIC to keep displaying the open hood warning under normal conditions since the sensor triggers easily on human voice and many other sounds.

 

Problem 2. I've looked around the builder's manual and couldn't find any wire that carries an "alarm armed" signal. Therefore, the best I could think of doing is creating an inverted RAP signal - when retained power accessories go off, the audio sensor powers on. Yes, this may mean that the hood will be sensed as open by the OEM alarm in the time between taking the key out and arming the system (i.e., by locking the truck). I don't think this will be a problem because the OEM alarm will wait for all doors to shut in order to arm the system. I might be missing some condition under which this could be a problem?

 

Going towards executing this, I prepared everything and the weather has been slowing me down. Basically, I will add one relay that will be able to close the hood switch, and another one that will cut the power to the sensor when RAP is enabled (or conversely, supply the power to the sensor when RAP shuts off). I am looking forward to completing some tests and reporting back results. I also plan to add two magnetic switches to the sensor (one for the tailgate and one for the bed cap rear glass), as well as another audio sensor in the bed of the truck (for my cap), but putting sensors in parallel is a breeze if this ends up working.

 

Notes: There are a plethora of wires one can tap into to achieve this, and for my specific truck configuration I think signals in the schematic below will work. Also, you could probably get away with just shorting the hood open switch signal to ground (instead of the low reference), but I just wanted to minimize any possible effect on the OEM system. Additionally, the mentioned sensor drives a low level on the signal output, which I have ignored in the schematic - this can be converted to a high level to drive a relay with a simple transistor circuit or perhaps with another relay. Maybe even the audio sensor driving low level on the output could be connected directly to the hood open switch signal without any additional components, but like I said, I just wanted to minimize any possible effects on the OEM system.

 

 

 

 

 

 

 

 

Edited December 27, 2019 by Vuk
Added remote start handling

[Vuk]

Update from today: The left side of the schematic is working properly - I can see that the sensor is powered only after the key is taken out and the driver opens the door (i.e., RAP goes off). On the right side I have not been successful in finding the hood switch wires in the X115 engine/body harness connector. It should be super easy to tap directly into the hood switch, but it got dark and a little cold to work outside so I called it a day. I will report back when that part is done and the testing stage comes up.

 

Edit: I did just realized that I missed something: the hood switch is not just a plain switch but adds a specific resistance between the wires (different when open/closed). So, it won't just be "shorting the wires with a relay", but a bit more than that - I will make sure I post an updated schematic once all is figured out.

Edited December 18, 2019 by Vuk

[AdioSS]

Interesting. I like this idea!

[Vuk]

OK, so the general wiring is laid out and I couldn't finish it today because of that wire grommet on the firewall... Spent too much time on that with no success.

 

Back to the audio sensor, it seems to be working well, and just a couple repetitive knocks on the windows with any metal tool are all it takes to set it off. Note that this specific sensor will not detect punches against the windows or body panels. Within a couple of days I will update the schematic with the diode-resistor that are needed to emulate the hood switch.

[Snowcamo]

OK, so the general wiring is laid out and I couldn't finish it today because of that wire grommet on the firewall... Spent too much time on that with no success.
 
Back to the audio sensor, it seems to be working well, and just a couple repetitive knocks on the windows with any metal tool are all it takes to set it off. Note that this specific sensor will not detect punches against the windows or body panels. Within a couple of days I will update the schematic with the diode-resistor that are needed to emulate the hood switch.

Might want to figure in a tilt sensor as well. These days they either use a black box to disable the alarm or and tow it. I have met a few who have had both so im going aftermarket myself.

Side note last I used said setup the tilt sensor wired in parallel iirc.

Sent from my LG-G710 using Tapatalk

[Vuk]

I am trying to stick with the OEM alarm/fob system just because I don't want too many new things in there, but to add a few cheap sensors myself clearly is easy enough.

 

I wonder if it's hard to add the OEM tilt sensor? It might just be easier to use the hood switch as a hook for an aftermarket tilt sensor.

[Snowcamo]

I am trying to stick with the OEM alarm/fob system just because I don't want too many new things in there, but to add a few cheap sensors myself clearly is easy enough.
 
I wonder if it's hard to add the OEM tilt sensor? It might just be easier to use the hood switch as a hook for an aftermarket tilt sensor.

Your guess is good as mine. Honestly until now I've yet to hear anyone speak of attempting to make modify the stock alarm. Kinda cool actually. [emoji482]

Sent from my LG-G710 using Tapatalk

[Vuk]

I just discovered one problem with this approach. When the engine is started with remote start, the accessory power is not turned on until the ignition switch is turned. Therefore, since the glass break sensor remains active, the engine will shut down the first time the "open hood" state is detected (which is likely due to the noise of the keys rattling). 

 

The core of this challenge is obtaining the "armed" signal - I am willing to live with the above problem for now since I have other higher priority mods on the list, but my next take on this would be to try to generate a signal that resembles the "armed" state more closely than inverted RAP. Right now, I will continue adding a shock/vibration sensor, a tilt sensor, and magnetic switches on the tailgate and the bed cap glass, as well as a glass break sensor in the bed.

Edited December 20, 2019 by Vuk

[Snowcamo]

I just discovered one problem with this approach. When the engine is started with remote start, the accessory power is not turned on until the key is turned in the lock. Therefore, since the glass break sensor remains active, the engine will shut down the first time it detects an open hood (which is likely due to the noise of the keys rattling). 
 
The core of this challenge is obtaining the "armed" signal - I am willing to live with the above problem for now since I have other higher priority mods on the list, but my next take on this would be to try to generate a signal that resembles the "armed" state more closely than inverted RAP. Right now, I will continue adding a shock/vibration sensor, a tilt sensor, and magnetic switches on the tailgate and the bed cap glass, as well as a glass break sensor in the bed.

Sending a pm

Sent from my LG-G710 using Tapatalk

[Snowcamo]

I just discovered one problem with this approach. When the engine is started with remote start, the accessory power is not turned on until the ignition switch is turned. Therefore, since the glass break sensor remains active, the engine will shut down the first time the "open hood" state is detected (which is likely due to the noise of the keys rattling). 
 
The core of this challenge is obtaining the "armed" signal - I am willing to live with the above problem for now since I have other higher priority mods on the list, but my next take on this would be to try to generate a signal that resembles the "armed" state more closely than inverted RAP. Right now, I will continue adding a shock/vibration sensor, a tilt sensor, and magnetic switches on the tailgate and the bed cap glass, as well as a glass break sensor in the bed.

This was suggested as a fit for my alarm project and I believe its right up your alley as well. https://www.compustar.com/accessories/das-ii/

Sent from my LG-G710 using Tapatalk

[Vuk]

That looks great but I am not sure if that device exposes an output that can be used without one of the compatible main units - that is can it be used to directly drive relays?

[Snowcamo]

Very good question. I will be getting my alarm and I'll be sure to add it to the list. I will find out what it is capable of controlling.

Sent from my LG-G710 using Tapatalk

[Vuk]

I edited the schematic in the first post to include components required to "emulate" the hood switch operation - diode+resistor in parallel to hood switch. This is neccessary because the hood switch does not simply ground out the signal wire when the hood is opened, but rather changes resistance.

 

I think I have a simple fix for the remote start issue which I will soon test and post my findings; otherwise the sensor has been working predictably for the past week.

[Vuk]

The Run/Crank Ignition signal can be found right there in the X51L left instrument panel fuse block, and I think that would be enough to fix the remote start problem. So, according to the updated schematic, the sensor power supply will be cut off if either the accessories are on, or the engine is cranking/running.

 

Scenario 1: You unlock the truck, sit in the seat and the moment you turn the key, audio sensor is disabled and you won't get hood open warnings (because RAP signal disables the sensor)

Scenario 2: You perform remote start and as soon as cranking is initiated, audio sensor is disabled and there is no chance of an open hood condition during remote cranking/running (because RUN/CRANK signal disables the sensor)

 

I will try to wire this today/tomorrow and this should wrap up this specific mod (I still haven't had time to wire up the remaining of the sensors though...).

[Vuk]

I can confirm that this now works, that is, remote start is not bothered by the sensor any more. In short, my audio/tilt/shock sensors and tailgate switch are always emulating the "hood open" condition, except when either the engine is running or accessories are on (in that case the sensors are not active).

 

One of these days I will modify the schematic to show how to go from the ground output to positive output on the sensors and that should conclude this mod. Anyone who has some experience with wiring relays could do this, if interested.