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Author Topic: Operating servo/strike latch for secret compartment using -stock- buttons  (Read 1667 times)
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I have seen many projects where the Arduino is just powered right off the vehicle 12V, but personally I would put a 9V regulator (LM7809 would be fine) before the Arduino and some big smoothing caps and place it as close to the Arduino as possible. Use 25 to 50V caps on the side towards the car battery. A 1000uF to 2200uF cap. With this and the regulator, it should protect the Arduino. The 7809 can take a voltage up to 35V.

For the solenoid power itself, just connect that to the vehicle power directly and switch it with whatever flavor you like such as an automotive relay, SSR, etc... In a bit of over-engineering, you could use an optoisolator on the Arduino output to ensure voltage spikes don't somehow make it into the Arduino. Or even just a 5.1V Zener between the output and ground (or even just a diode in series since it is always an output to prevent current from entering.)

Again, this is probably not really necessary, but those are suggestions to protect things and parts are cheap. They would go in my own design. And likely will soon, as I have a trip computer planned in the near future.

If the switches are wired all in series, all switches would need to be closed at the same time. Make sure the switches use the same ground that your Arduino uses.

I'm not sure what you mean by a relay on the switches. A switch just closes or opens a circuit. It doesn't generate voltage on its own. However long wires in the car may develop large spikes of current on them. Again a zener would help here. It would just go between the Arduino pin and ground. That would sink any volatge over the 5.1V to ground and away from the Arduino. Or you could use optoisolators here as well, but you would need to provide voltage to the switches on the other side of the the opto isolator. Go with a zener to keep things simple.

Just keep in mind that if you do wire the switches in series that they all need to be pressed at the same time to register. So lay them out accordingly so that all CAN be activated at the same time. You could not do a specific sequence this way. And realize there is a chance that it could be accidently activated this way unless you layed it out in some way that it would be very unlikely that all switches would get pushed at the same time (for example by people sitting across all the switches at once.) It would certainly be simpler to wire up and code that way, though.
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I have seen many projects where the Arduino is just powered right off the vehicle 12V, but personally I would put a 9V regulator (LM7809 would be fine) before the Arduino and some big smoothing caps and place it as close to the Arduino as possible. Use 25 to 50V caps on the side towards the car battery. A 1000uF to 2200uF cap. With this and the regulator, it should protect the Arduino. The 7809 can take a voltage up to 35V.

For the solenoid power itself, just connect that to the vehicle power directly and switch it with whatever flavor you like such as an automotive relay, SSR, etc... In a bit of over-engineering, you could use an optoisolator on the Arduino output to ensure voltage spikes don't somehow make it into the Arduino. Or even just a 5.1V Zener between the output and ground (or even just a diode in series since it is always an output to prevent current from entering.)

Again, this is probably not really necessary, but those are suggestions to protect things and parts are cheap. They would go in my own design. And likely will soon, as I have a trip computer planned in the near future.

If the switches are wired all in series, all switches would need to be closed at the same time. Make sure the switches use the same ground that your Arduino uses.

I'm not sure what you mean by a relay on the switches. A switch just closes or opens a circuit. It doesn't generate voltage on its own. However long wires in the car may develop large spikes of current on them. Again a zener would help here. It would just go between the Arduino pin and ground. That would sink any volatge over the 5.1V to ground and away from the Arduino. Or you could use optoisolators here as well, but you would need to provide voltage to the switches on the other side of the the opto isolator. Go with a zener to keep things simple.

Just keep in mind that if you do wire the switches in series that they all need to be pressed at the same time to register. So lay them out accordingly so that all CAN be activated at the same time. You could not do a specific sequence this way. And realize there is a chance that it could be accidently activated this way unless you layed it out in some way that it would be very unlikely that all switches would get pushed at the same time (for example by people sitting across all the switches at once.) It would certainly be simpler to wire up and code that way, though.

Hi! Thanks for the great advice - much of it will be incredibly useful, however I think some of my comments were misinterpreted. When I was talking about wiring in relays in series I meant using the wiring of the stock buttons as outlined in the graphic below



I assume I would need something like a relay so the voltage of the stock circuit doesn't fry the board. However, I have no idea as to what kind of component to use for the 'green box' - it's like a relay in reverse I guess - using a higher voltage circuit to switch a lower voltage. Does anyone have any practical tips on how I could make this work?

Thanks!

Scott
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Your stock button is likely to be getting pulled up and is shorted to ground when pushed. So, the negative side of the switch would always be at ground.

The main consideration here is not to disturb the functionality of the original switch (I assume that you would still like to be able to use your rear defroster.)

I would tap off the positive side and use a comparator. Your other options are a relay, and you would connect the coil to the positive side as well, but that would mean the coil was always energized until the button is pressed. And it may draw enough current that it is sensed as a switch pressed. A zener diode is another option, but may end up also drawing too much current (a zener will conduct when the voltage is above its threshhold.)

A comparator will have a high enough impedence as to not disturb your stock circuit.
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Your stock button is likely to be getting pulled up and is shorted to ground when pushed. So, the negative side of the switch would always be at ground.

The main consideration here is not to disturb the functionality of the original switch (I assume that you would still like to be able to use your rear defroster.)

I would tap off the positive side and use a comparator. Your other options are a relay, and you would connect the coil to the positive side as well, but that would mean the coil was always energized until the button is pressed. And it may draw enough current that it is sensed as a switch pressed. A zener diode is another option, but may end up also drawing too much current (a zener will conduct when the voltage is above its threshhold.)

A comparator will have a high enough impedence as to not disturb your stock circuit.

Yes - I would definitely still like to use the original functionality of the switches I'll be messing with smiley Thanks for the advice on how to do it correctly.

Another question as well (sorry - I've asked a million already). As the pins on the board don't have a positive and negative, I assume I would attach the ground on the board to the car body, and then as you said, tap off the positive side, correct?

Cheers smiley
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Use a multimeter to determine that. Car body is not always ground, some chassis have positive on the body. You will need to use a multimeter to determine how the switches are wired up anyway. It is probably as I mentioned, but safer to double-check than to assume. smiley
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Will do - just wanted to say a big shout out for everyone's help here - excellent community!
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Hiya again everyone - I'm not entirely sure this is the correct section of the forums for posting this, but figured it would be useful to tack it on to the end of what people have already read.

Would anyone be interested in me creating a tutorial whilst I develop my project based on the advise I've gotten here? I will post the tute in the appropriate area of the forums.

Cheers,

Scott
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The gallery would be the appropriate section. I think the general advice is that someone will always benefit from a well documented project, so I encourage it.
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Your stock button is likely to be getting pulled up and is shorted to ground when pushed. So, the negative side of the switch would always be at ground.

The main consideration here is not to disturb the functionality of the original switch (I assume that you would still like to be able to use your rear defroster.)

I would tap off the positive side and use a comparator. Your other options are a relay, and you would connect the coil to the positive side as well, but that would mean the coil was always energized until the button is pressed. And it may draw enough current that it is sensed as a switch pressed. A zener diode is another option, but may end up also drawing too much current (a zener will conduct when the voltage is above its threshhold.)

A comparator will have a high enough impedence as to not disturb your stock circuit.

Hi again smiley do you know what kind of comparator I should use? (and also how I should wire up the circuit? Assuming the vehicle body is ground) Sorry!!! I'm a bit of a no-hoper once it comes past basic components...
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Hi all - being the total noob I am, I was hoping you could assist with something else. I need to decide what sort of servo to purchase that would be appropriate for the project. I intend to have a bolt slide through a small block attached to the bottom of the 'coin holder' in the door (which you will be able to take out to reveal the compartment). It will therefore need to be able to withstand moderate lateral force.

Does anyone know what kind of servo I should buy (and where from!?) for this purpose?

I hope the pic below outlines how I expect the bolt will operate.



Thanks so much for all your help smiley
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Regardless of what you use, I would not rely on the motor to handle that force. There should be a block on the bottom of the coin holder and a block in a fixed point. The bolt would always be in the fixed block, but could slide into the other block.

In that configuration, the two blocks and the bolt take all the load. Placing them against each other would increase their strength.

A servo would work, but a solenoid would make more sense. Doorlock actuators are very cheap.
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Great idea smiley

Thanks!
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