Vetinari Clock: Lighting the Vacuum Tube with LEDs -

Vetinari Clock: Lighting the Vacuum Tube with LEDs


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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15 thoughts on “Vetinari Clock: Lighting the Vacuum Tube with LEDs

  1. “Actually, I hadn't really thought of doing it quite that way, but its not a bad idea — I'll give it a whirl the next time I have a spare minute.”

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  2. “Seeing as the clock has in part Discworld as it's founding idea, a flat disc balanced on the backs of four elephants which, in turn, stand on the back of a giant turtle, Great A'Tuin. What better than seconds made up of four elephants stamping in time tha

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  3. “I have to admit that the thought of this clock sitting on the back of four elephants with their feet stomping out the seconds is strangely appealing….”

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  4. “This is really great-looking! Quite an attention-grabber. You'll have this in a booth at ESC to get everyone to come over, right?nnThe burnout problem in the video is because the camera is taking the scene average brightness to set the exposure. So t

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  5. “Thatks for the kind words Steve — I think it would look awesome at ESC — but it's my baby — I'd be scared to make it travel anywhere — however I will have some great pics and videos of it as part of my talk on Using Awesome Analog Meters. Will you be

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  6. “@max: actually, the nastiest part of the UBM site is that it TRAPS you. If, for example, I click on a link to embedded from a post of yours on EET, I cannot go back to EET by “backspacing” (or any equivalent) no matter what! It just sends me to the UBM

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  7. “That's my fault — when I create the links, I set the “open in a new window” option — so backspace won't work — but you can always kill the new window and then you'll be left in the old one.nnI could do it so that clicking on a link appears in the s

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  8. “Have you come across the new twist on EE Times- you click on the comment link on the top right hand side where all the comments appear and it takes you to the comment, as desired. Then an advert pops up- if you click the X to cancel it, you are left at th

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  9. “Max, have you thought about syncing the LEDs to the seconds? I see you have 16, so that implies a change every (just under) 4 seconds. You could maybe change the color or add a color every change time, or light one more led every change, or have all the

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  10. “Talking of Terry Pratchett, I have only just put two and two together. (Yeah, don't tell me, I'm a bit slow…) I saw his documentary Choosing to Die some time ago – it was very good and he came across as a first-class guy. I've only jsut realised that t

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  11. “@Max – it's still more elegant to link some text to a hyperlink….and I put jsut instead of just and I can't correct it….and when I click on your comment in the list it only takes me to the beginning of the blog, not to the comment, and I still can't b

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