Can I use the RTC power to change state of alarm circuit?

I'm just getting started with my Uno, and havent gotten an RTC (real time clock) chip yet. I'm attempting to use the arduino to monitor an alarm, in a special situation (sorry for the ambiguity) and want to see if this is feasible. And what components I would need.

I need to use the RTC battery to set the state of an alarm (which is a separate circuit) to its "on" state. So that the alarm is activated when power is reconnected. Thats all it needs to do while unpowered, its not powering an alarm, its merely closing a switch (or relay) on the alarm circuit if a physical switch is closed while power is out (or disconnected). The alarm only sounds when power is reconnected by design.

In reality there probably is a different or better way to do this (please advise) but this is how I imagine it operating in my head. There would be an output circuit running off the RTC when there is no power supplied to the arduino.

output rtc power to the monitored switch if switch is closed it completes the circuit to the relay which flips the relay to the on state.

and last I need to do this for 6 identical circuits.

Thanks so much for any help

edit:removed unnecessary function

So I've cleared up some things about how I'm hoping this will work. I'm hoping I can output some power from the rtc chip when under power, or the rtc battery power to a transistor array chip... With each of 6 transistors pointed to 6 alarm circuits.

http://www.mitsubishielectric.com/semiconductors/content/product/icsensor/transistorarray/tarray/tarray_lv4/m63805kp_e.pdf

When a switch is closed the transistor sends a pulse to close the appropriate relay setting the alarm circuit to its on state. If under power the alarm is activated immediately, if power is off the alarm will be on when power is reconnected.

The alarm will be reset programmatically through a separate circuit.

I'm new to this, so any advice is greatly appreciated. Especially if this sounds unfeasible for some reason.

Does this sound like something an (or any RTC chip) can do--ie will any of them send their battery power to a different chip, or do I need to rig a connection to the battery separate from the chip?

Thanks, Steve

It is difficult to give advice, given such a vague description of what you want to do.

The outputs of most ICs can supply power to other circuits (usually only a few milliwatts), however open collector or open drain outputs are an exception. The specifications and limitations of the outputs will be found in the manufacturer's data sheet for the RTC you choose.

The batteries on the RTC modules are normally button cells, and are only designed to run the RTC circuit when there is no external power.
They are not intended for any other use, and I'd not try running the Arduino let alone a relay from that battery

Also. when you mention "relay", a normal relay requires constant power to be energized.
I think you can get special relays that don't have internal springs to open them again when the contacts are closed (or vice versa) but I can't recall what they are called.

Either way, your whole concept sounds flawed.

Why can’t you program your Arduino so it goes straight to the Alarm state when it starts up if there is an alarm condition?

I don’t see what the RTC has to do with anything?

It doesn’t sound (!) like much of an alarm if it can be switced off.

…R

rogerClark:
They are not intended for any other use, and I'd not try running the Arduino let alone a relay from that battery

A bare ATMega/ATTiny microcontroller can run happily off a coin cell if it spends most of it's time sleeping. But I agree, powering an full-on Arduino with it's higher power consumption with a coin cell seems like a non-starter.

Most relays also require a few dozen mA to energize, which will probably cause the coin cell's voltage to drop below 1.8V causing the microcontroller to crash or reset.