# 4-LED Octal Clock Demands Colorful Math

We’ve all seen LED clocks where RGB LEDs are used to display time. It seems like the simpler the interface, the more likely you’d need to do math to figure out the time. This Octal Clock by [Alex Kurrasch] proves the point by using only four LEDs: the top two show hours and minutes, and the bottom two LEDs are multipliers.

Using octal numbering, [Alex] translates the data using a Venn diagram of color mixing. The mapping uses 1 as red, 2 as green, followed by yellow, blue, magenta, and cyan. It ends with 7 as white (all on) and 0 as black (all off).

As the time changes, a fading algorithm changes the display to match. He offers the time of 7:38pm as an example in the grid shown here. Base-8 math is provided; don’t worry, you’ll get really good at this if you make your own wristwatch version… people will learn to never ask you about the time.

The clock uses a ATMega64 running assembly language firmware with a DS1306E+ RTC chip keeping track of time. The enclosure is cool too; [Alex] milled the case out of mahogany and the front and back plates are anodized aluminum. The unique looking diffusers on the LEDs are actually paraffin, a trick that [Elliot Williams] mentioned in his recent article on diffuser materials.

## 12 thoughts on “4-LED Octal Clock Demands Colorful Math”

1. I really do have to question the use of a CPLD to drive the LEDs. He does note that discrete CMOS chips could be used instead, but how he arrived at a CPLD before thinking of a simple shift register escapes me. Is there some subtlety in the design I’m missing?

1. just guessing, but it might have gone somewhere along the lines of “oh hey I have this CPLD in my junk box…. might as well use it!”

2. Backwoods Engineer says:

Nice, but should do a “resistor color code” RGB clock. That color code I have memorized, since age 7…

1. Agree, but I must recognize that the color enumeration schema presented on the Octal Clock site is a good design too.

2. Lennart says:

But this color scheme is easy to get, connect b0 to red, b1 to green and b2 to blue.

3. John Baichtal says:

how do you do brown? kind of a dark red?

3. John says:

Why has the world forgotten the difference between mathematics and arithmetic?

1. jonmayo says:

Arithmetic is a branch of mathematics …

1. John says:

But why use such a broad term when it is easier and more informative to use the term that more closely defines the subject.

It’s the same as saying “I got a new vehicle” rather than “I got a new car”.

4. Now the next invention should be to make a surgery robot, and make it complex enough that the doctor would require to decode some script during each stage of the surgery. We humans make things to make life easy, not calculus hard…

5. fireant says:

I really like that clock scheme, even more than that one binary clock with six squares where hours, minutes and seconds were mapped to rgb and overlaid. The compact square format looks good, and it’s really cool that it is also a binary clock at the same time (if you dissolve the color mixing). Very nice!

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