So. One of R2-D2's notable features is a circular two-colour light under his eye. On the original physical props these had red and blue gels that would slide back and forth, changing the colour of the light. Builders of full-sized R2 replicas call this light a "PSI" for "process state indicator," and generally use Arduinos programmed to drive blue and red LEDs that simulate the effect.
For a small R2 model (the Bandai 1:12 R2), I wanted to avoid the expense and hassle of programming an Arduino just to get the effect. Plus even the smallest board is too big for the tiny model, and most microcontrollers run at 5 volts, not off two AAs or a 3v lithium.
So I considered a few things:
- You can buy super cheap kits which use a 555 timer and a 4017 decade counter to drive a sequence of 10 LEDs. The 10 sequential outputs could be used to drive a pair of LEDs, which could alternate. But then you have a circuit board which won't fit inside a small R2 model.
- You can get 3mm LEDs which automatically flash, alternating between red and blue. Compact, simple, and they run off two AAs. However they don't dim between colours, and the flash rate is much too fast. R2-D2 on speed!
- You can get 3mm tricolour RGB LEDs which slowly cycle through a sequence of colours. Again, these require no external circuits and can run off 3 volts. But the green light in the sequence is wrong.
So I got to thinking, what if you got rid of the green diode altogether? After all, tricolour LEDs contain three separate diodes housed inside a single transparent case. The tiny silicon die making up the diode is wired using an unbelievably thin wire.
And that was the answer! I examined the lit LED carefully, figured out which side the green diode was on, and roughly filed that side of the LED flat. Then I used a 0.3mm drill and slowly drilled a tiny hole into the LED, testing as I went, until I severed the wire that powered the green diode.
Done! I now have a 3mm LED that runs off 3 volts, and which slowly fades continuously between red and blue. The one drawback is that there's a short period where no light is emitted at all, as that's the point in the sequence when the green diode would have been lit alone. But since R2's light occasionally looks like it's off, I figure that's good enough.
Now, this doesn't help with the rear dome PSI (yellow and green), nor the flickering fibre optic lights. But for less than £1, this is a pretty zero-effort solution. Hope this helps someone!
For a small R2 model (the Bandai 1:12 R2), I wanted to avoid the expense and hassle of programming an Arduino just to get the effect. Plus even the smallest board is too big for the tiny model, and most microcontrollers run at 5 volts, not off two AAs or a 3v lithium.
So I considered a few things:
- You can buy super cheap kits which use a 555 timer and a 4017 decade counter to drive a sequence of 10 LEDs. The 10 sequential outputs could be used to drive a pair of LEDs, which could alternate. But then you have a circuit board which won't fit inside a small R2 model.
- You can get 3mm LEDs which automatically flash, alternating between red and blue. Compact, simple, and they run off two AAs. However they don't dim between colours, and the flash rate is much too fast. R2-D2 on speed!
- You can get 3mm tricolour RGB LEDs which slowly cycle through a sequence of colours. Again, these require no external circuits and can run off 3 volts. But the green light in the sequence is wrong.
So I got to thinking, what if you got rid of the green diode altogether? After all, tricolour LEDs contain three separate diodes housed inside a single transparent case. The tiny silicon die making up the diode is wired using an unbelievably thin wire.
And that was the answer! I examined the lit LED carefully, figured out which side the green diode was on, and roughly filed that side of the LED flat. Then I used a 0.3mm drill and slowly drilled a tiny hole into the LED, testing as I went, until I severed the wire that powered the green diode.
Done! I now have a 3mm LED that runs off 3 volts, and which slowly fades continuously between red and blue. The one drawback is that there's a short period where no light is emitted at all, as that's the point in the sequence when the green diode would have been lit alone. But since R2's light occasionally looks like it's off, I figure that's good enough.
Now, this doesn't help with the rear dome PSI (yellow and green), nor the flickering fibre optic lights. But for less than £1, this is a pretty zero-effort solution. Hope this helps someone!
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