Vetinari Clock: Lighting the Vacuum Tube with LEDs

March 13, 2015

Max The Magnificent-March 13, 2015

This is just a brief update with regard to my Vetinari Clock project (see also So Many Projects; So Little Time).

One rather tasty feature of the clock is an interestingly-shaped vacuum tube mounted on the top. Sitting just under this tube I have a 16-element NeoPixel Ring from Adafruit.

These things are great. Each element contains super-bright red, green, and blue LEDs, and each LED has an associated 8-bit pulse-width modulated (PWM) controller. The elements are daisy-chained together, and you can control the whole thing using a single pin from your microcotroller.

If you take a peek at this video, you'll see some of the lighting effects I've been playing with:

Unfortunately, my camera really doesn’t do this justice, possibly because the LEDs are so bright. The problems with the camera give you an appreciation for the tremendous range of brightness that can be accommodated by the human eye.

We start with a simple "breathing" effect in which all of the pixels fade up and down together. I'm currently using 20 steps from fully off to fully on, and vice versa. Also I'm using linear increments between steps, with a 0.1 second pause in the middle of the cycle (fully on) and again at the end of the cycle (fully off). If I decide to use this effect, I'll time it such that it takes exactly one second to perform a complete cycle, but at the moment I'm just approximating things.

As I say, I'm currently using a linear ramp as depicted by trace (a) in the illustration below. I've been wondering if other waveform envelopes would look any better, such as the ones shown in (b) and (c) below. I'm sure a lot of research has been done in this area. If you have any thoughts on this, please share them in the comments below.

I really wish you could see this in real life. The effect with two white pixels chasing each other around on a red background (i.e., all the other pixels are red) is pretty impressive. I also tried two red pixels on a bright white (full on) background, but the red ones were washed out. However, this does look good if I dim the white background LEDs down to a dim glow.

Another effect that looks very tasty is having a bunch of four white LEDs racing round, with the lead LED being fully on and the other three of diminishing rightness fading to a dim pink background.

The way this ring is positioned, there are two LEDs either side of the 3 O'clock, 6 O'clock, 9 O'clock, and 12 O'clock positions (with 6 O'clock being the one closest to the observer at the front of the clock.

As you'll see in the video, one effect starts with two white LEDs at the 6 O'clock position, then we illuminate additional LEDs to the left and right (clockwise and anticlockwise) until we reach the 12 O'clock position, then we turn them back off again until we end up back at our 6 O'clock starting point.

I also tried stating with two LEDs lighted either side of the 3 O'clock and 9 O'clock positions, and then turning additional LEDs on until we reach the 6 O'clock and 12 O'clock positions, but we would really need more LEDs to make this look effective.

So, that's the current state of play. As I say, this looks pretty awesome in the real world; I only wish I could capture a better video. I will certainly try to do so. In the meantime, can you think of any other effects I should try?

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