"Stranger Things" Lights

erco

Senior Member
My daughter is a fan of Netflix's show "Stranger Things", where a boy lost in another dimension (the "Upside Down") can communicate by lighting up alphabet Christmas lights individually. Coincidentally, she is just now asking to learn to code, so this was the perfect chance to build a 20M2-powered sign for her room. 26 LEDs are multiplexed using just 6 output pins, so there is plenty of room for expansion. Beepers (she wants to learn Morse code, also used in that show) and sound effects and IR control and...

Who says you can't learn anything from TV?

 

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tmfkam

Senior Member
I bet she is thrilled with that! What a "groovy" Dad. (Feel free to replace groovy with a more "with it" phrase)
 

AllyCat

Senior Member
Hi,

"Charlieplexing" can use each (Tri-State) Output pin to drive both a Column and a Row. But obviously a LED Anode and Cathode cannot be connected to the same pin, so the matrix array diagonal cannot be used. Thus 6 pins can drive 6 * 6 - 6 = 30 pins. Each PICaxe pin can be tri-stated by using an INPUT or a REVERSE command, or all pins (on the same port) by using the DIRS variable.

Cheers, Alan.
 

Buzby

Senior Member
I'd be interested to see how you did the Charlieplexing. The code I used for the Orrey was one way of doing it, but it might not be the best !.
 

hippy

Technical Support
Staff member
So, you switch into high-z by making the Pin an input, right?
That's correct. Individual pin control can be had using INPUT or "DIRx.y=" commands. Entire sets of pins can be controlled using the "DIRSx=" command.
 

AllyCat

Senior Member
Hi,

Yes, I always use INPUT <pin> to tri-state it. There are numerous other PICAXE commands such as REVERSE (which toggles between Input and Output modes), FORWARD, BACKWARD, BRANCH, BUTTON, etc., which you probably only ever discover when you try to use them as a label or a variable/constant, and get a "syntax error" instead. :)

Cheers, Alan.
 

erco

Senior Member
Glad you boys like it. Yes, tri-stating saves the day again. Spelling out " I LOVE YEDLSIN" here, which is an inside family joke about how daughter Lindsey often misspelled her name as a child. But she is a programmer now!

 

Jeff Haas

Senior Member
Wow, fun! I haven't seen someone use Charlieplexing that way before. Usually people make those LED cubes.

I did something similar when the show was first on, but I used some of those WS2812s that look like holiday light bulbs. Here's a picture of it in front of the T-Rex skeleton at the California Academy of Sciences - they asked me to bring it there for an evening event!
25121
 

manuka

Senior Member
Magnificent, but I must have had a sheltered life as the show is unknown to me. Mmm-30 gives 4 spare after A-Z so scope for more => 1, 2, 3, &, @, $, ? etc
 

bogbean

Member
Nice one Erco, it looks fun. My nephew is learning to spell so I might have to pinch your idea. Thanks for sharing it.
 

oracacle

Senior Member
Years ago I used Charlie plexing for a clock
It's possible to make very large displays providing you have the pins and the processing power.
 

Buzby

Senior Member
... It's possible to make very large displays providing you have the pins and the processing power.
Yes, you can make very big displays using Charlieplexing, but no amount of processing power will overcome it's biggest limitation, 'persistence of vision'.

Because you can only illuminate one LED at a time, in order to display more than one you have to pulse each LED for a short time. For example, if there are 10 LEDs on show, then each is energised for 10% of the time, and for 20 LEDs it's 5%.

When you're down to a 5% duty cycle then flickering becomes noticable, and also the effective brightness is much reduced.

Charlieplexing works best if only a smallish number of LEDs are lit, and it doesn't make any difference how big the full display is, the processing power needed stays the same. ( Another problem is if you need a mixture of different coloured LEDs, because different coloured LEDs need different drive currents. )

However, one great advantage of Charlieplexing on a PICAXE, as well as not using many pins, is that driver chips are not needed. Because only one LED is energised at a time the total current remains the same no matter how many LEDs appear to be lit. This means the 20mA capability of the PICAXE pins is enough to drive the LEDs directly, with just a resistor on each pin to limit current.

Charlieplexing is great. I'd like to build another huge Charlieplexed device, but I can't think of what to make.
( I'm open to suggestions, but NOT another clock !.

Cheers,

Buzby
 

erco

Senior Member
You can actually have several LEDs on at a time, based on how they are wired up, as you can see in my videos & pics. Never more than half, since they are arranged in opposite polarity pairs. I'm guessing maybe a third of them could be on simultaneously through various binary PINS combinations. Careful design layout could yield some useable patterns.
 

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David HK

New Member
You really are a good man.

At the age of 73, I wonder if I could inspire you to teach your daughter correct spelling and usage as follows.

The difference between the alphbetical letter 'O' and the numerical figure zero '0'. It is very important in the modern world. People working in the disciplined services, police forces, armed forces, aviation and so on have to know the difference.

In this regard can you extend your magic light show to include the numerical figures, 0 to 10, and then invite her to recite strings of numbers - telephone numbers for example - so that she grows up well educated on the basics.

There is no reason why your invention should not catch on in the education arena, I hope it does.

Best wishes,

David
 

papaof2

Senior Member
I've always thought that learning Morse should be an immersive experience - visual of the letter, stereo sound with the letter pronounced in one ear and the di-dahs (at 15WPM, adjustable) in the other ear. Whatever a person's best learning mode, that should cover it. Looks like you have more than half of that.
 

erco

Senior Member
I think I'm having more fun with this than my daughter! Morse code is so much fun, I gotta get my code speed back up to 13+ WPM. Now the ST lights can decode & display letters it hears in Morse code.



Screenshot from show of their vintage Heathkit ham shack:

Ep1-Heathkit.png
 
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