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I have a project that would seem to be ideal for Arduino, but want to run it by some experienced makers as a reality check.

I have no current experience with Arduino, but am confident that I can handle the IDE and programming. Just want to make sure everything I want to do is feasible.

I want to build something like a geo puzzle box, except that it won't open at a particular place, it will open after a particular time and date. That time might be years in the future.

Two main components are needed: the main Arduino board, and some mechanism for determining the current time/date.

The primary challenge, as I see it, is battery life. I'm currently considering a system using exposed battery leads. The user would connect a battery to the box before trying to open it.

To get the time, I was going to use GPS at first. The GPS module would be powered by the same battery that powers the main board. But then I found clock shields with 5 years of stand-by power from a coin battery. However, this would limit how far in the future the open date could be set to, and I'd have to deal with the possibility of having the clock battery die before the open date.

When the correct date has been reached, the system will drive a servo that will allow the box to be opened.

So, some specific questions:

- Can the Arduino run a "boot" routine when power is applied? I want the box to immediately startup and check the date after a battery is connected.

- Can it check somehow for whether the clock module has power (i.e., the battery is still good), and execute some action if it doesn't?

- I'd like to the final product to be as small as possible. Can I develop on something like the Uno, then swap that out for a Mini when I'm ready to finish the box? Or shuld I start with the Mini? Will there be any issues with the Mini driving a servo?

Any thoughts or comments would be appreciated.
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Can the Arduino run a "boot" routine when power is applied?
Yes, it does.

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I want the box to immediately startup and check the date after a battery is connected.
It won't be immediate, but it will be pretty quick.

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Can it check somehow for whether the clock module has power
Not without modifications to the clock module (connect the battery leads to an analog pin and ground).

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and execute some action if it doesn't?
What would that action be? If the clock is dead, it no longer knows the time. The only appropriate action that I can think of is to open the box.

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I'd like to the final product to be as small as possible. Can I develop on something like the Uno, then swap that out for a Mini when I'm ready to finish the box?
Yes.

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Will there be any issues with the Mini driving a servo?
Driving a servo, no. Powering the servo, yes. Don't do that.
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I would go with a standalone design & skip any regulators, LEDs, etc that draw power & don't do anything for you.
Look at smaller parts too, ATTiny13, since you don't need a lot of IO.
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PaulS

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What would that action be? If the clock is dead, it no longer knows the time. The only appropriate action that I can think of is to open the box.

Exactly. If I ask for the time, and none is available (for whatever reason), open the box.

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Driving a servo, no. Powering the servo, yes. Don't do that.

I think I understand what you mean - the Arduino will switch the servo, but not provide power to it. Correct? I assume there are examples of this online.
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Well in terms of the time, if the box has no idea what time it is (due to no RTC, or dead RTC battery), you could have a backup system with an ethernet shield, and there is a plug for the ethernet port on the outside of the box, and the Arduino would attach to the network and do a NTP request (maybe talk to a server to see if there is some other reason to open the box).

Similarly with a wifi shield, though there might not be an open wifi network for it to use.

Finally if you have a GPS sensor, that provides accurate time.

Of course, it may be useful to have a backdoor so you can open it without it being the correct time.
« Last Edit: August 21, 2012, 04:40:03 pm by MichaelMeissner » Logged

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