The second prototype is built. A dedicated daughterboard now houses the sensor, two LEDs, and a pushbutton; it's been hot melt glued on the face of the washer, over the "Door Locked" light. 

Anyhoo: One LED is green, and shows whatever the current state of the "Door Locked" LED is. The other is blue and shows if the -inator is in an "alerting" mode. 

The button *could* be a self-destruct button – what kind of inator would this be without one? – but, at least for the moment, I think I'll use it as an "acknowledge alert" button to make it stop playing music.

Some fairly simplistic logic ties all of this together:

There are some more hardware changes. Since I went the "more I/O" route, I'm embracing the Uno and forgetting about going back to the ATTiny85. I'll probably use an Arduino Pro Mini (5v, 16MHz) in this; I've got a couple still lying around.

The audio is now differential output (pins 3 and 11). And I'm using the Shutdown pin on the amp to power it off when I'm not playing back; saves power and, more importantly, limits the hiss coming out of the quick-and-dirty audio output. To rights, it should have some basic filtering (a couple capacitors and resistors). I'm running filter-free at the moment and damning the consequences. We'll see how long it is before that bites me in the ass.

This build's raison d'etre? More testing: does the sensor stand up to real world use, or does it accidentally trip (positively or negatively)? What should the alert restart backoff delay be? Is a single button interface sufficient? I hope to answer all of those this weekend so I can move this toward finished.

And what, exactly, will "finished" be like?

It probably won't be pretty. This washer is over 15 years old; I don't know how much longer it will last. We've had to repair it a few times already and I'm tired of opening it up. The next failure might be the deal-breaker for me, which makes me think spending a lot of time on this probably doesn't make sense.

But it does deserve a better notification system than just blaring music in the basement, hoping someone hears it. At very least, some LED pulsing while it's getting ready to play; I'd like it to not take me by surprise. And I suppose I'd also like to turn down the intensity of the LEDs with some PWMs. They're kind of blinding at the moment.

Ideally? I want this to notify us on our phones.

I'm working on a simple SIM800L GSM module interface that should be able to text us easily enough. When Hologram announced their developer program with a free 1MB/month data transfer, I happily spent $5 for a SIM - waiting for the day that I'd want to embed lightweight cellular comms in something. And here's a fine candidate! If I can move away from SMS and get the SIM800 to use that 1MB of data, I can bootstrap off of one of my servers at a hosting company and have that machine send an SMS to our phones.

If that doesn't pan out, I've got another possibility sitting in a junk drawer: back in 2009, I picked up a WiFly GSX breakout board from SparkFun. I used it for a capture-the-flag type event once. It's a fiddly mess of a product, but would probably do fine in this particular application...