TV Remote-Triggered Projection LCD Clock

(Uses No Lenses!)

Any TV or other IR remote pointed at this will turn the light on, projecting the time onto the nearest wall.

What This Is

This is a clock that projects the time onto the wall of a darkened room whenever any IR remote control (like a TV remote) is pointed at it and any button is pressed. It uses no lenses. The time is displayed for as long as any button is pressed.

This was partly inspired by the Projection Clock Project at raphnet.net. My implementation is different and has some extra knobs on it, but I think our projects are tied in the ugliness department...

Why This Is

Mostly this is a "because it's there" project, but there is a somewhat practical goal. Our TV room is nice and dark, but lacks a clock. A constantly-lit clock would be a distraction and nobody who uses the room wears a watch. However, when sitting down to enjoy a movie or watching MythTV a remote control is always close at hand.

So this clock is placed off to the side, where it does not pick up any IR signals from normal use of the PVR or television. To project the time onto a side wall, you point any remote off to the side and press any button!

How It Works

The Projector Part

The projector part is simple. A large-digit LCD clock is used for the time display. A Luxeon LED is used to provide the light.

The LCD clock is opened in order to tamper with the polarizer (which should be a clearish-grey film on the LCD glass) - turning it 90 degrees results in a reverse image display, and simply reversing the polarizer should give the same effect. (This is done also in the aforementioned projection clock project). I had to cut the polarizer film into a few squares since it wouldn't fit in the new orientation, and I also blocked out some pieces I didn't want passing any light with some aluminum tape.

The LED is a LXHL-PW01 Luxeon Emitter LED. It's pretty ordinary as far as the Luxeons go - and it's only 3$ at this writing. The LED makes a pretty good point source of light and there is no funny focusing of the light done by the LED's packaging. That combined with the large digits of the LCD clock meant that I didn't need a lens! I actually got a fine projected image (within about 6 feet or less) without using the lens I had on hand. That was a pleasant surprise.

The IR Part

To pick up generic IR signals from a remote control, I used a 38kHz IR receiver unit (they are very common, and are often used in robotics - particularly Sumo Robots - for object sensors). A 36kHz or 40kHz receiver will still work, but range will be shorter (unless your remote happens to actually emit 36 or 40, in which case range will be better!)

The IR receiver output triggers two garden-variety 2N3904 NPN transistors to drive the Luxeon LED at about 50mA. I could safely go up to 100mA through the LED without adding a heat sink to it, but 50mA was bright enough for my purposes.

As long as the IR receiver is seeing infrared from a remote, the LED will be lit and the time will be displayed.

How To Make It

1. Modify the LCD Display

Some of the parts I used (and the method I used to assemble things) were highly dependent on the contents of my junk box, but I didn't use anything too weird. In fact, the most specialized thing I used was the Luxeon LED - which is inexpensive, and available by mailorder to anyone from luxeon.com. Or you can also use the Canadian distributor luxeonstar.com .)

First, a see-through style LCD clock. (Also shown is a lens I would later discover I did not need.)

The first thing to do is modify the clock by peeling off the polarizer and sticking it back on 90 degrees off (reversing it should also work, but mine was adhesive and I wanted to keep it "stuck". Choose whatever method works for you and your particular clock.) As previously mentioned, the polarizer on your clock will probably be a greyish-clear film on the LCD display itself.

2. Build the IR-sensor and Driver Circuit for the LED

Here is what my completed circuit looked like, along with the test setup. Note that the LED must project light into the FRONT of the LCD clock for the projected image to be correct (otherwise it will be mirror-imaged.)

After testing, I glued things to a piece of plastic and hot-glued the LED onto a solid-core copper wire to allow for adjustments. Then it was covered with a simple black matte shell (not shown - I used a cheap black plastic toolkit) to block any stray light, and placed in a convenient spot in the TV room, and it was done!