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Author Topic: Operating servo/strike latch for secret compartment using -stock- buttons  (Read 1680 times)
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Hi all  smiley

Yay! First post. Let me preface myself by stating that I have no intention of creating a 'car trap' that is used to smuggle anything illegal. I am simply fascinated by secret compartments, and was inspired by a recent WIRED article that discussed them (they're not illegal in Australia by the way - which is where I am  ). I wouldn't mind using it to hide valuables in my car though when I park it in the city though!

I have limited experience with Arduino, but tend to take to new concepts fairly well.

The project I would like to build is a secret compartment in a car that can be operated by pressing a combination/sequence of -stock- buttons (i.e. defroster, power windows etc), which would then in turn activate a servo to lock/unlock the compartment.

I have identified a hollow space that would be perfect for the compartment (rear door coin tray that screws out, and leaves a big gap underneath). I'd love to design it in such a way so that I can unlock the mechanism with the stock key combo, then slide out the coin holder, which would uncover the compartment.

Any help anyone could give me would be incredibly appreciated!

Please let me know if there's any other info I can supply that will help with my query (e.g. photos, diagrams, the original article etc)

Thanks!!

Scott
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Does your car have CAN bus or anything similar where you might be able to capture all these stock key presses?
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Wow!

Thanks for the very prompt reply. The car does have an easily accessible OBD2 diagnostics port, and one of the protocols it can communicate with is CAN BUS. I'm not sure how I would go about using the interface between the buttons and the ECU/BCM though.

Cheers,

Scott
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First you might make a few application decisions I would think.
First the power default state.

 Do you wish the lock to remain locked if all power is lost in the car as in a dead battery or something causing the vehicle to loose power, making access impossible without first re-establishing vehicle power? Or do you wish power required for the lock to be locked, thus creating a continuous battery drain when the vehicle is parked? That would have a bearing on what you use to activate or deactivates the locking mechanism be it a solenoid or servo or come up with some very low current device.

Lefty


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Unfortunately now I am going to disappoint you: Neither do I. Though I had read that some vehicles interface just about every button in the car through the CAN bus.

I would spend some time over in the mp3car.com forums.

I do know that more than a few people have done OBD projects with the Arduino. Here is a library that look pretty good:
http://www.arduinodev.com/arduino-obd-ii-library-gets-updated/
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Use a solenoid latch powered from the fuse bus and controlled via a pushbutton under the dash. Sometimes simple things work best.
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Consider the daffodil. And while you're doing that, I'll be over here, looking through your stuff.   smiley-cool

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First you might make a few application decisions I would think.
First the power default state.

 Do you wish the lock to remain locked if all power is lost in the car as in a dead battery or something causing the vehicle to loose power, making access impossible without first re-establishing vehicle power? Or do you wish power required for the lock to be locked, thus creating a continuous battery drain when the vehicle is parked? That would have a bearing on what you use to activate or deactivates the locking mechanism be it a solenoid or servo or come up with some very low current device.

Lefty




I was just ticking that over actually - I think I'd like to go for the 'fail secure' option, purely for the fact that I would like to keep my options of latching mechanism open, and I'd hate to come back to my car after a period of time and find it had a dead battery if I din't get the design spot-on!

Thanks!
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Unfortunately now I am going to disappoint you: Neither do I. Though I had read that some vehicles interface just about every button in the car through the CAN bus.

I would spend some time over in the mp3car.com forums.

I do know that more than a few people have done OBD projects with the Arduino. Here is a library that look pretty good:
http://www.arduinodev.com/arduino-obd-ii-library-gets-updated/

Thanks! Hopefully someone can point me in the right direction with this.
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Use a solenoid latch powered from the fuse bus and controlled via a pushbutton under the dash. Sometimes simple things work best.

Very much agreed - would be much easier. I would really like to give this a shot though - it's incredibly fun.

Thanks for your input though smiley
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First you might make a few application decisions I would think.
First the power default state.

 Do you wish the lock to remain locked if all power is lost in the car as in a dead battery or something causing the vehicle to loose power, making access impossible without first re-establishing vehicle power? Or do you wish power required for the lock to be locked, thus creating a continuous battery drain when the vehicle is parked? That would have a bearing on what you use to activate or deactivates the locking mechanism be it a solenoid or servo or come up with some very low current device.

Lefty




I was just ticking that over actually - I think I'd like to go for the 'fail secure' option, purely for the fact that I would like to keep my options of latching mechanism open, and I'd hate to come back to my car after a period of time and find it had a dead battery if I din't get the design spot-on!

Thanks!

I would certainly feel better with a fail-secure system. If someone is trying to get into your car and your alarm is going off, one thing they might do is kill power to the car. Just don't lock anything in there that would be needed to restore power to your car. And as for the latch needing constant power to stay locked or even unlocked would be a very poor design anyway. Your gas cover latch or trunk latch doesn't take constant power in either case, does it?

Personally, having been stuck with a dead battery before, I ALWAYS carry a battery operated jump starter in my trunk. In fact, it saved me just a few weeks ago!
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It's incredible how quickly even a relatively small current can drain a car battery - not to mention, even if it's not fully drained, too low a voltage can make the computer act all screwy!
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I was thinking, it's not absolutely necessary for the board to pickup the signal through OBD to recognise it's been pressed. I'm sure that the majority of buttons (with the exception of things that require resistors like fan motors) are either power on or power off.

Would it work to hook up to the wires running to each switch (window up/down) for example, and assign that to a pin? Then I could do the same thing for several others, and write some code that would only allow the solenoid to open if the inputs were triggered in the correct order?
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Of course. That's why you would connect it to your Auxillary circuit that is powered only when the ignition is in the ON position. You wouldn't be able to read you CAN codes otherwise anyway.

I am with making things a bit simpler as well, though. A well hidden button or even a few buttons would be just as effective. I wouldn't put them under the dash or in the glovebox though. Consider inside your upholstery. Or even reed switches that you activate with magnets in a certain sequence.

You have a certain amount of security through obscurity. How common is it that someone would have a hidden compartment in their car? Unless you made it very obvious, they wouldn't even know it was there and wouldn't be looking for buttons to open it.

It's worth pursuing, but there is no guarantee that you will have CAN codes for the stock buttons in your car.
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That's an awesome idea actually! (Reed switches or buttons under the upholstery)
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A couple of queries if I'm going to take the approach of just connecting wires to the switches themselves to detect when they are switched on/off and use this to trigger the solenoid:

1. How would I connect up the wires to the two wires coming off the back of each switch appropriately? I was thinking it would need to be in series to detect the voltage change - which will then I assume require relays so as to not fry my board!

2. Does anyone have any experience powering a board from a vehicle? (e.g. does anyone know what would be the best way to connect the board to a stable source of power (i.e. current, voltage))

Thanks thanks thanks in advance smiley

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