Monday 14 April 2014

Space Invaders alarm clock mod

I'm very conscious of the fact that the last two posts have been quite text-heavy, so here's a lighter weekend project.

I was once given a Space Invaders alarm clock. It's shaped like one of the aliens from the game, the 'pixels' of the LCD display are shaped the same, and when the alarm goes off it makes the aliens sound and moves from side to side as they did in the game.

Which is all well and good unless you have a small bedside table, and the clock just rolls off the edge every morning...

The lazy answer would be to just build a barricade, or some kind of stand that would stop the wheels turning.

Opening up the clock reveals a small PCB, with wires neatly labeled, and a small motor which operates a worm gear to move the wheels.


My plan is to replace the motor, and use it's wires to power some LEDs which I will place in the 'eyes' of the model.

Although labelled "M+" and "M-", the motor wires polarity changes - to allow the change of direction. This is great for motors, but reversing the polarity on an LED will likely result in the magic smoke escaping.

To get around this - and also provide a neat colour change effect - each eye will have 2 LEDs in parallel, and arranged in opposite directions. The LEDs of each colour for each eye will be in series (see below). Also don't forget a 100 Ohm resistor at one of the ends (doesn't match with one)

One green and one red LED per eye. As the current changes the LEDs will alternate

This means that when the current is flowing one way, it can't get through one LED, so moves through the other. When it changes direction, it can no longer get through that one, so it diverts to the other, effectively 'blinking' each LED in turn.

Then it's just a case of drilling eye holes, poking the LEDs through, and reassembling (I also used hot glue to act as a diffuser for the eyes)

Each stage of the end result. It doesn't roll off the table anymore, but I didn't count on it looking a lot more sinister.

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