Goal: Add a motion sensor that lights up the clock at night when it detects movement, and make the backlight brightness manually adjustable.
Why: I only have a few requirements for a good bed-side clock. It needs to be easily visible, but not light up the whole room. I am nearsighted, so I've always wanted a projection clock so I could see the time on my wall/ceiling in big digits. But the "visible" and "not a bright nightlight" requirements are somewhat in conflict, right? What if the clock was dark until you waved your hand above you, and then suddenly the projection appears! Perfect solution, for me at least. Why no one sells this, I simply don't understand. So, we'll have to make one.
How:This instructable is not complete yet! It will evolve in (at least) two parts. This first part is a proof-of-concept disassembly/reassembly, to get an idea what the innards look like and make sure it would be feasible to add features into the clock. I'm not someone who is adept at microcontrollers and electronics, however, so I will be partnering with a friend to do all the modifications. My goal will then be to add more information to this instructable and "complete" it for posterity and others who think this is a neat idea to try.
The subject: The RCA RP5440 was chosen for its features, form factor, and affordable price. The time on the front panel is nice and large, and unlike most projector clocks this one doesn't look like part of a spacecraft. The projector is aimable, and the case is a good hefty size, which I hoped would mean ease of disassembly and some room for new brains inside. It also has oodles of other features that I don't need or care about, but hey, free features.
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Step 1: Blue Canary in the Outlet by the Light Switch
The front panel display on this clock is mega bright. Like I could read by it in an otherwise dark room. I don't need a night light; my room is already bright enough from miscelleneous computer equipment and a nasty sodium safety light that's mounted outside the window.
The problem with this bright display is that there's no way to turn it down, so that's something we'll have to address.
Step 2: No User Serviceable Parts? We'll See!
There are four corner screws and a smaller one centered on the top-back of the unit. These come out first; don't let your cat eat them.
The back cover will then fairly easily hinge open, pivoting slightly on its bottom latches. Once you get to this point, you can lift the back cover off enough to get to the next step. There are several wires bridging the circuit board to components attached to the back cover: transformer, battery compartment, and speaker. Fortunately there's enough slack on them to let us do our work. Just be gentle.
Step 3: Getting Board
Looking at the main board, there are some white wires on a connector that run power and data lines down to the display level. But nothing as helpful as "display light". Those connections must be split off later on somewhere; we'll have to dig deeper.
The two daughter-boards on the top and left sides are seated in little channels, but the big main board is held very firmly in place by three plastic clips.
I found it easiest to begin with the top right clip, then do the top left, and finally the bottom center one. You have to apply some lift pressure to the board while moving the clip out of the way, or else you won't make any progress.
Step 4: Need a Lift
Doh I forgot to take a picture at this step.. I'm sure we can fill it in later once the mods start taking shape.
Basically you can lift the main board up fairly easily now. You'll be pulling the daughter boards out of their guide rails, and unseating a bunch of those plastic-hinge switch contacts, but it's no big deal as long as you're careful.
Then, lift up the shield enough to check out the display electronics. There are two separate power taps for the display lights, one set of red/black wires going to each side of the display where they connect to the bulbs. The locations where these wires connect to the board is where I think we'll have to intercede with a brightness control of some kind. I didn't think at the time to check whether the two sets of connectors were electrically common despite their different board locations. They probably are.
Step 5: What Other Mischief Can We Get Into
On my agenda was opening up the projector unit, for a couple reasons. I wanted to see whether it would be possible to put a brighter LED in it (spoiler: it's not possible). OK but mostly, I just wanted to get in there and, you know, check it out.
It turns out that there's not much inside the projector itself that will be of use in this project. But getting this little enclosure open was such a bear that I just have to document it here for posterity.
If for some reason you want to open this up, I recommend to follow the exact order and steps that I did in the pictures. This part of the device is a little more fragile, and unlike the main clock it's all snap-fit. >(
Step 6: Looks Like Some Kind of Robot Flashlight...
In this step I explore the guts of the projector.
Step 7: Closing Thoughts
OK so putting the main enclosure back together should just be reversing what you did to take it apart, right?
I noticed a couple little "gotcha"s, and I tried to document them in the images here.
After you get the unit back together, you'll have to re-set the clock. The manual is very light on details of this clock's "auto set" feature, but as near as I can tell they just set it at the factory and it ships with batteries installed. The manual says if the batteries die you can manually set the clock.. This is what leads me to suspect that, unlike some of its bretheren, it does not attempt to sync with the atomic clock signal or anything.
It's just as well... Now that daylight savings time has been changed, all those fancy-pants clocks that set themselves will be wrong for several weeks a year. Woops!