LED Clock: LED Numbering Order

The Question

This totally doesn’t matter, and OTOH it’s a little aesthetic touch I want to get right. What should be the order that the individual LEDs are numbered within one character?

This impacts two things: circuit layout and LED test patterns. I’m ready to start laying out the circuit, which is why I’m thinking about it now. I’ve thought about LED test patterns, which is why I’m thinking about it at all.

The LED drivers shift in their data bit by bit, while shifting their current contents out in the same fashion. So if you want to enter 11111111 into a driver currently containing 00000000, it works like this:

00000000 ← 11111111
00000001 ← 1111111
00000011 ← 111111
00000111 ← 11111
00001111 ← 1111
00011111 ← 111
00111111 ← 11
01111111 ← 1

The Impact

This means it’s very easy to do moving marquee type of effects by shifting a single 1 bit or a short row of 1 bits through a display:


Just shift a few 1 bits into the register, then keep clocking it and latching the input register to the output register on every clock cycle.

Now, granted, the 6276 is so fast compared to human vision that I could shift in an entirely new pattern from scratch, then latch it, way faster than you could possibly see. But there’s a certain elegance in taking advantage of the driver’s architecture for the design of a test pattern. So I’d like to arrange the LEDs to do just that–make a pleasing test pattern when activated in order from D0 through D30. (Not a typo–only 31 LEDs in the design.)

The Proposal

Here’s what I’ve come up with, drawn a couple of different ways:

LED Order LED Order

The test pattern starts in the middle of the digit, loops through the upper half clockwise and the lower half counterclockwise, springs off the right edge to the top of the colon, and drops down into the period. The possible issues are:

  • Is this even the right kind of pattern to do?
  • Is that the right starting point, in particular with respect to the extra LED inserted in the lower half to smooth out the 2?
  • Is it right to skip the middle-right LED on the way down, and leave it for the end before jumping up to the colon? Or should it be included on the way down, and skipped on the way to the colon?

I’m open to suggestion, but I’m also afraid that it’ll be hard to evaluate the visual smoothness of the effect for sure until a digit is prototyped–and I can’t prototype on a breadboard; it’ll require a custom PC board to do it. I guess if I were sharp enough with computer animation, it shouldn’t be that hard to do this in software; but at this point, I’m not sure I’m up to it. Maybe I should pull out my old C-64 . . .

One Response to “LED Clock: LED Numbering Order”

  1. Muaz says:

    I’ve had no problems lighting several LEDs at the same time. Just repeatedly serial input the pattern (data, clock) and wait till the pattern is complete before latching it. Then blank (output disable) and repeat the pattern for the next digit. You might have to play around with the refresh rate to avoid flickering.

    As per the brightness of the LED, the single external resistor can control the brightness for the entire series of LEDs. It works with mine, and if it still doesn’t work, adjust the duty cycle.

    I’m not sure if you can do the animation in Photoshop, but I’ve been doing some of mine with Macromedia Fireworks. Works like a charm — avoids resaving the file multiple times too :)

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