Darlotech Ltd

It was nearly Christmas and I was preparing the decorations. Normally I go with lights on the tree and some lights around the room. As usual the problem with the latter was no existing suitable hooks to fix a string of lights to. My thoughts wandered to a projected image. The one I had in mind projected an image of Santa in his sleigh, pulled by his reindeer. I found a couple such projectors available. They had some sense of movement, the sleigh was static but there were shimmnering objects around it. I bought one and opened it up. What I found was surprising, there were four LEDs and each one shone through a transparency, three with objects at slightly different positions, one of Santa. The three ‘object’ LEDs were illuminated in turn, the Santa LED was permenantly on. I simply blanked off the object transparencies and so only had the Santa image projected. Next was to get some real movement.

I suppose I could have gone down the route of using a proper projector driven by a PC but thst would be expensive and you wouldn’t want one of those switched on 24/7. Also I wanted Santa to fly across the whole wall, a projector wouldn’t have the beamwidth.

The solution I arrived at was to mount the santa projector onto a platform, controlled by a servo motor. This meant I could rotate it back and forth. Then, to get a mirror image of Santa (I didn’t want Santa to fly forward one way and reverse the other) so he was always flying forward, I used a mirror. Best explained by the following diagram.

The servo motor rotates in the same direction from A-B-C (Santa flys from right to left), then with the servo motor going in the same direction, the projection is reflected off the mirror and the image goes from left to right. So the start and end positions of santa are at the right hand side of the wall, but the servo would be fully clockwise (for the start) and fully anticlockwise (for the end).

To repeat the cycle the servo is returned from fully anticlockwise to fully clockwise during which time the LED is turned off. To control the servo motor and the LED I used an Arduino nano.

This was only part of what I needed though.

The next step was to add the sound of Santa and his sleigh, but the sound had to follow the sleigh across the wall. I needed to play the sound through two speakers (stereo) and fade the sound between the two in line with Santas position.

I had naively thought a digitally controlled potentiometer would do the trick. I was wrong, these are really only good for handling DC voltages, not audio signals.

In the end I did the belt and braces thing and used a servo motor to control a duel ganged (real) potentiometer which varied the fading from a ‘Santa’ signal from an MP3 player.. The on’off of the LED was switched by a digitally controlled MOS switch. All controlled by the Arduino.

Here’s the result (or a still from it at least)