The only real UPS solution for me where I live is "RCT", a UPS manufactured by a local PC Hardware supplier.
It has a USB port, but I can't find any details about it. I've even contacted the manufacturer specialist via email, but He doesn't seem to like answering potential customers, so I'm hoping that I can get your opinion here.
I want to use the UPS (650VA) to power a Raspberry Pi (2). The Pi will be monitoring freezer temperatures and will email the owners if their temperatures rise above a certain preset value. However, this all means nothing if the Pi looses power because no-one knew that the power was out.
This now becomes a question of "How can I determine whether the AC-in on the UPS is being powered". I've been trying to think of a number of really cheap, yet elegant ways to accomplish this, and the one that I've decided on is, quite unusual and I'm wondering if it's a good idea.
The UPS comes with a standard piezo-buzzer. When the lights go out, the UPS goes into battery-mode and emits a loud beep every few seconds. So I was thinking of linking 2 GPIO ports on the PI to the buzzer in parallel and monitoring it for power. If it's "buzzing", then the power is out and everyone important gets an email letting them know that they need to start making a plan to fix whatever went wrong.
I could even take it a bit further and determine the frequency of the buzzer (not the pitch, but how often the buzzing happens), and when the buzzing is once every second, send another email letting everyone know that the UPS is on it's last legs. (0.2Hz = Battery mode, 1 Hz = very little time left).
Good idea? Bad idea? I look forward to hearing your input.
P.S. Another solution that someone had was to buy a cheap (network) switch and plug it into the Pi (and power it from the mains). The idea behind this would be that when thee power goes out, the network will drop. Fine, but I don't really want to go buy more unnecessary hardware if it can be avoided.
P.P.S I have a spare Raspberry Pi that I'll be using for this. I'm comfortable with Raspbian and it works for what I want to do.
P.P.P.S The UPS I want to get is very cheap. I don't want to make too much of an effort building a custom home-baked UPS system. And I'm not too concerned about the energy efficiency loss because of the DC-AC-DC conversion.
Unlike the question here, My question is whether the solution that I proposed is a feasible one.