After the renovation was done I still had an empty light block sitting above the side door outside, and an ugly hole in the kitchen ceiling with wires hanging out of it. The wiring hole going out through the wall did get temporarily sealed up in an easily removable way, as I intended to eventually put *some* kind of light outside and feed the power out to it. What I wanted was something like a typical motion-detector outdoor light, but also a way to utilize the sensor to alert me inside whenever it triggered on. I also wanted better control over the light itself, since there's no point in for example turning it on when someone comes to the door in the daytime. A few products had entered the home-improvement market that came close to the functionality I wanted, but none of them quite fit the bill. |
Besides, in theory I already had all the components of a simple but solid system, including a trashpicked infrared-detector outdoor light and my old doorbell parts. The doobell hadn't been functional for years anyway and its wiring through the basement was long since history, but the "dinger" was still on the wall in the hallway and the little electrical box with the transformer had come off the fusebox during the upgrade. Why not put those pieces back together? I would just have to figure out how to tap into the detector trigger output and fire the doorbell briefly, and it would be totally appropriate. | |
After thrashing around with tentative designs involving relays and
timing circuits and whatever else, I decided the easiest way to go was
use the AC output to the light to also power the doorbell transformer
for some small time interval. Conveniently, the original light system
had the sensor module and the output triac separated inside with a
simple three-wire interface between them -- to keep AC high voltage out
of the sensor electronics and the small wiring going to it, presumably.
I would just need a longer wire between them and to bring the AC module
to the indoor side of the wall where I'd have control over its output.
I anticipated four possible states:
The required routing and switching would actually fit inside the old fuse-box for the doorbell transformer, so that seemed like an elegant solution to work toward. A bit of rooting around in junkboxes turned up a rotary switch that could do three positions and some appropriate wire to connect everything up. This would go through a new connector in the transformer box. The initial alert idea was some kind of passive time-delay circuit with a rectifier and large cap to power the doorbell only momentarily, but ultimately that didn't really work out. The doorbell sounder elements are basically steel bars like a xylophone, mounted on loose rubber grommets next to resonance tubes tuned to roughly the same frequencies of the "ding" and the "dong". Those actually do help amplify the sound a little. For this purpose I only really wanted the initial "ding" and replaced the larger bell-bar with a small metal bracket for the solenoid to return against. Before being put back together the detector module got an LED added to shine through the lens and show when it was actually seeing movement, so I could diagnose the pattern when walking around in front of it. That required a bit of digging into its electronics, but there seemed to be a convenient couple of spare open holes in the circuit board right about where an LED and a series resistor would connect -- probably for the purpose, although the original unit didn't come with any indicator. The circuit appears very similar to the one detailed here [PDF, 143K] on page 9, but sans relay output. It also needed a photosensor bypassed inside which would otherwise disable triggering entirely if it was light outside. Sensible if it was only driving a light, but not what I needed as I wanted the motion signal to always be active. Some modules don't have that feature, such as whatever some neighbors down the road have; their driveway light pops on any time someone passes by. That was kind of hilarious during all the road construction. |
I could fish wires through the hole in the wall but not any sort of
suitable connector without significantly enlarging it, so I had to get
up here and attach the connector pins after the wires were through and
foam-sealed at the outside. I used one of the 9-pin circular ones like in
the wheel speed hack for the car,
the male side of which could nicely chassis-mount in the top of the box.
It carries the sensor interface in, and the lamp AC back out.
In the "mighty have fallen" department, yeah, the generic reading-glasses made this a lot easier. Kind of ironic to think that I used to work on small mechanical watches by naked eye when I was a kid... |