tinkering with charlieplexing

Charlieplexing is a cool little method of controlling lots of LEDs from far less than lots of microcontroller pins.
It's not a new thing, but its something I never really got around to playing with - until now.
references:
circuitdigest....
www.instructab...
en.wikipedia.o...
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This isn't the only way to do it.
It's probably not the best way to do it.
But it's how I do it.

[@AnotherMaker]

Seriously one of the best explanations that I've seen. Great video.

[@tomgeorge3726]

Nice video, I have some charlieplex pcbs that I got ages ago on Aliexpress. Good fun to play with and produce a nice LED array display.👍👍👍

[@richfiles]

I've been aware of charlieplexing for ages, but this is the first time I'd seen the technique used to drive optocouplers. Very nifty idea indeed!

[@davidv1289]

Thanks for an interesting video. It is a well documented but little known fact that Arduino pins programmed as inputs are high impedance. This allows them to be used with tri-state logic such as a data bus - I use this to allow an Arduino to emulate RAM, ROM, and EEPROMs in microprocessor controlled test equipment for troubleshooting purposes.

[@SouperDaveCDN]

An internet salute: o7 from a fellow Canadian. Keep up the good work and casual teaching and learning. Cheers

[@sdgelectronics]

I seem to recall it originating in a Maxim app note, back when they posted them out monthly. I had it working on a parallel port on a PC in the absence of no microcontroller hardware

[@pileofstuff]

That sounds like a fun hack.

[@MarcRidders]

Congrats, 6k+ subscribers.

[@KARLLARK100]

as always love your vids,.//., going to try this later ta for the input,.//.,

[@AndyCallaway]

This is relevant to my interests.

[@TheEmbeddedHobbyist]

I just think of it as keyboard scanning in reverse. Nice looking beer.

[@ClaudioRay]

How did you still achieve the tri-state using the optocoupler and the 2n2222?

[@pileofstuff]

The tri-state happens in the microcontroller. The LED section of the optocoupler acts like a normal LED and lights or not based on that.

[@ClaudioRay]

@@pileofstuff hey! Thanks for your answer. I more or less get how the tri-state work on the microcontroller pins, however I still cant understand how are you able to drive those more power demanding leds still using charlieplexing (which requires those three states) and given the higher voltages you are no directly using the uC pins.

[@pileofstuff]

@@ClaudioRay the LED side of the optocoupler makes use of the tri-state capability of the microcontroller pins, just like any LED. That's where the "magic" ends. After that, the photo-transistor output of the the optocoupler acts like a normal switch, and anything beyond that assumes that it's just being switched by a normal transistor.

[@ClaudioRay]

@@pileofstuff Yeah... sadly is very tough to maintain the tri-state logic and drive high-voltage GPIOS. I have been struggling to drive high voltage LEDs under charlieplex configuration with no luck so far. If you get an idea on how to, please drop me an answer.

[@celtisafricana4984]

An a analogue shift register (without latching)? I have an unhealthy love for shift registers on my arduino

[@JasonSimpson1966]

Unless you are running two independent and separate power supplies, an optocoupler CANNOT be completely isolated between the input and output sides.

[@pileofstuff]

That's correct, thanks for reminding people. It is what I was doing, but I didn't really mention it specifically. . One power supply is the little black power bank that the Digispark is plugged into, and the other is partially visible in the lower left (in the segment after 12:47 you can see it's current display changing as the various LEDs go on and off).

[@JasonSimpson1966]

@@pileofstuff In all fairness, though, and also for clarification, opto-couplers are often used in single supply circuits. In these instances, though, there is generally a transformer in use which physically isolates the two sides of the circuit.

[@pileofstuff]

I used to find them commonly in stage lighting dimmers to isolate the control side from the high power side.

[@markfergerson2145]

Cool video. Long ago when I worked at a systems integrator we used Charlieplexing driven by PLC outputs in some commercial equipment. By the way- did I miss something? What happened to Mailbag Monday this week?

[@pileofstuff]

Mailbag Monday is every second week. I'd go broke doing it every week (even with my patreons helping me)

[@markfergerson2145]

@@pileofstuff Figures. We're sill sort of n lockdown here in Lower B.C. (Washington state) and those silly numbers on the calendar have been running togehter the last couple of months.

[@adam850]

Good idea with the optoisolators. I have a 100-pack of some Sharp optoisolator in a bin somewhere... I suspect that the other commenter has these too. The PC817C.

[@SidneyCritic]

That reminds me, I have to chase up my Sharp opto's I ordered 160 days ago - lol -.

[@SteveRobillard]

Congrats on making hackaday's links.

[@North49Radio]

Pretty cool. hackaday.com/2020/06/14/hackaday-links-june-14-2020/

[@MrMaxeemum]

Christmas lights also use this technique.

[@noggin73]

Nice. My (super cheap) optocouplers have 4 pins though.

[@pileofstuff]

That's also common. They simply don't have the base broken out to a separate pin - just the collector and emitter, plus the LED anode and cathode.

[@adam850]

Sometimes two out of six of the pins of an optoisolator are N/C anyway.

[@GnuReligion]

These devices come in so many flavors. Like others here, I only have PC817's. Perhaps there are applications where a fixed current gain is not adequate, so the gate needs a pin.

[@sidharthap]

Blinking LEDs are good n all... scroll down to the end of this www.pcbheaven.com/wikipages/Charlieplexing/ article and try Charlieplexing switches!

[@bollie9752]

Today It feels like monday....

[@AJB2K3]

I found charlieplexing used on rechargeable battery packs